Abstract

We have investigated resonance effects in high-order harmonic generation (HHG) within laser-produced plasmas. We demonstrate a significantly improved harmonic yield by using two-color pump-induced enhancement and a 1 kHz pulse repetition rate. Together with an increased HHG output, the even harmonics in the cutoff region were enhanced with respect to odd harmonics. We report the observation of a resonance-induced growth in intensity of 20th harmonic in silver plasma (2×), 26th harmonic in vanadium plasma (4×), and 28th harmonic in chromium plasma (5×).

© 2011 OSA

1. Introduction

Enhancement of HHG in gaseous media as a result of atomic and ionic resonances has been the subject of extensive theoretical work over the last ten years [15]. The most significant experimental results in this field were, however, reported for HHG in plasma plumes. Weakly-ionized plasmas from some solid targets displayed resonances in the excitation of neutrals at certain harmonic wavelengths [68]. These experiments also showed that singly charged ions can enhance the yield of specific harmonics. As a much wider range of solids are available compared with gaseous target materials, HHG studies in plasma plumes dramatically increase the chance of finding an ionic transition, which is resonant with a harmonic wavelength.

Several mechanisms explaining the origin of resonant harmonics in laser-produced plasmas have recently been proposed [913]. In [9], it was shown that the influence of atomic autoionizing states on the phase matching of HHG in calcium plasma may result in efficient selection of a single harmonic. This was the first report of efficient high-order harmonic selection by autoionizing states. The four-step model, developed in [10], predicts the enhanced generation efficiency for the harmonic resonant with the transition between the ground and the autoionizing state of the ion. In this model, the third (recombination) step of the three-step model of HHG [14,15] is divided into two steps: the capture of a laser-accelerated electron into an autoionizing state of the parent ion, and the relaxation of this state to the ground state accompanied by the emission of a harmonic photon.

It was found by Milošević [12] that the laser intensity dependence of the intensity and phase of the single harmonic generated in the resonant HHG from plasma ablation is different than that of the standard plateau and cutoff high harmonics. The resonant harmonic intensity increases continuously (i.e., without rapid oscillations) with the increase of the laser intensity, while the resonant harmonic phase is almost constant. Such unusual for HHG behaviour of the harmonic phase requires a detailed experimental investigation. Namely, the harmonic phase dependence is important for synchronization of high-order harmonics. The importance of the results [12] was highlighted by the recent reconstruction of a train of attosecond pulses produced through HHG in an ablation plasma [16]; the group of odd harmonics responsible for the pulse train encompassed a resonant harmonic. In order to understand HHG in the presence of such a resonance, a time-frequency analysis was performed in [13]. Consistent with the predictions of the four-step model [10], it was found that the resonance gives rise to a single harmonic in the HHG spectrum.

Resonant enhancements in HHG from metal and semiconductor targets ablated by picosecond pulses [17,18] have been previously studied using a single pump pulse at λ ≈800 nm. However, when HHG is driven by a two-color pump scheme, emission spectra can display both odd and even harmonics, increasing the chance of a spectral overlap with an ionic resonance. Another promising route towards locating additional resonances is to tune the harmonic wavelength. This could be achieved by various methods: tuning the fundamental wavelength of laser pulse [7,19]; chirping the laser radiation [2023]; altering the laser intensity to control the ionization rate of the nonlinear medium [2427]; and adaptive pulse-shaping [28,29].

Previous studies of resonance-induced and two-color pump-induced enhancement of harmonics in laser plasmas were demonstrated using relatively low (10 Hz) pulse repetition rate laser sources [7,30]. Increasing the pulse repetition rate to 1 kHz considerably increases the average power of high-order harmonics [31], and allows improved statistics in experimental applications of the emission.

An attractive feature of resonant enhancement is that it can increase the conversion efficiency of a specific harmonic by more than an order of magnitude [17]. In this paper, we combine resonant enhancement with two-color pumping at 1 kHz pulse repetition rate to generate strong harmonics in different spectral ranges. This unique source will be ideal for various applications in physics, chemistry and biology, and for advancing nonlinear x-ray optics and attosecond physics.

2. Experimental setup

These experiments were performed using a 1 kHz Ti:sapphire chirped pulse amplification (CPA) laser (Red Dragon, KML Inc.) delivering 2.5 mJ pulses of 40 fs duration at 780 nm. In these experiments a portion (1.5 mJ, 20 ps) of the uncompressed pulse was split from the beam line prior to the laser compressor stage. This pulse was focused to an intensity of Ips = 5 × 109 W cm−2 to 3 × 1010 W cm−2 on the target using a f = 400 mm lens, as shown in Fig. 1 . The beam spot of the ablation laser was measured to be 0.4 mm at the target surface. The target was moved constantly up and down manually during these experiments.

 

Fig. 1 Experimental setup: HPP, heating pump pulse; FPP, femtosecond probe pulse; M, mirrors; VC, vacuum chamber; T, target; FM, focusing mirror; FFG, flat field grating; MCP, microchannel plate; CCD, charge coupled device.

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The compressed pulse (30 fs, 1 mJ) was focused into the plasma in a direction orthogonal to that of the picosecond pulse using a f = 200 mm mirror. The position of the focus with respect to the plasma plume was chosen to maximize the harmonic signal. The intensity at the focus of the femtosecond pulse was estimated to be Ifs = 5×1014 W cm−2. The delay between plasma initiation and femtosecond pulse was varied in the range of 6 – 57 ns using an optical delay line. A flat-field grating (1200 lines/mm, Hitachi) and imaging microchannel plate (Photonis USA, Inc.) with a CCD camera were used to record the high-harmonic spectrum.

To drive HHG using two colors, the second harmonic (2ω) of the fundamental (ω) femtosecond pulse was generated using a 0.5-mm-thick BBO crystal in a type-I phase matching scheme. Group velocity dispersion between the ω and 2ω pulses in nonlinear crystal was compensated for using a calcite plate. The second harmonic conversion efficiency was 4%. HHG was enhanced by the presence of the 2ω field despite the 25:1 energy ratio between the ω and 2ω pulses.

The chirp of the femtosecond laser pulse was tuned by adjusting the separation of the two gratings in the CPA compressor. Only the wavelength at the leading edge of the pulse contributes significantly to HHG because at the intensity used the strong field induced plasma grows increasingly with time, eventually preventing HHG; thus the wavelengths of the high-harmonic comb from a chirped pulse can be controlled through this ionization gating effect [20,21,24,25]. We calibrated the chirp by measuring the spectrum, spectral phase, and pulse duration of the laser pulses as a function of grating separation using SPIDER [32].

3. Results

In this section we present the results of single- and two-color HHG studies using three different target materials: silver, chromium and vanadium. The used targets showed best stability at high pulse repetition rate among other materials, where resonance induced enhancement has previously been observed using the low (10 Hz) pulse repetition sources. The optimum delay between heating and driving pulses was found to be 40 ns for these three targets. Through the chirping technique, we are able to locate resonant enhancements of single odd, and in some cases even, harmonics.

Figures 2a and 2b show harmonic spectra generated in silver plasma in the cases of apertureless and apertured single color pump (780 nm). Harmonics above the 50th order were routinely generated. Apertureless pump means the single color pump without introduction of aperture in front of input window of vacuum chamber. Apertured pump means that the 7 mm diameter pump beam propagates through the 4 mm aperture before entering the vacuum chamber. Introduction of 4 mm aperture on the path of driving radiation in front of vacuum chamber changed the relative distribution of harmonics from being stronger for lower orders in the case of apertureless beam (Fig. 2a) to stronger higher order harmonics in the case of apertured beam (Fig. 2b) due to the propagation effects changing the phase matching conditions for different groups of harmonics.

 

Fig. 2 Harmonic spectra from Ag plasma in the cases of (a) apertureless and (b) apertured single color pump (780 nm). (c) Tuning of 17th and 19th harmonics by changing the distance between the gratings in the compressor stage. Positive and negative values of pulse duration correspond to positively and negatively chirped pulses. Dotted lines show the tuning of 17th and 19th harmonics with different chirps. Black lines show the wavelengths of these harmonics at chirp-free conditions. Thick black lines on the left side of bottom graph show the tuning range of 17th harmonic (2.8 nm).

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Variation of the laser chirp allowed a considerable tuning of harmonic wavelengths (2.8 nm in the case of 17th harmonic, Fig. 2c), while the relative intensities of harmonics in the plateau region remained approximately the same over a broad range of the driving laser chirps, which led to variation of pulse duration in the range of −97 fs to +110 fs (positive and negative values of pulse duration correspond to positively and negatively chirped pulses). Note that effective tuning of harmonic wavelengths through chirp can be achieved only for broadband pulses, where a pronounced difference in the wavelength components at the leading and trailing parts of the pulse can be produced. The pulses used in our experiments have a bandwidth of ~40 nm FWHM. In the case of variable chirp conditions, the conversion efficiency decreased by a factor 6 in the case of 97 fs negatively chirped pulses compared with 30 fs chirp-free pulses.

The introduction of a second-harmonic field increased the conversion efficiency of odd harmonics, in agreement with previous studies in gaseous [3338] and plasma targets [39]. The conversion efficiency of the harmonics in the long wavelength range of plateau was almost two times stronger in the case of two-color pump compared with the single-color pump. In the case of the silver plasma, we also observed strong even harmonics, at the same intensity as the odd ones (Fig. 3a ), which extended into the cutoff region in some cases, as seen in Fig. 3b. Tight focusing (f = 200 mm) led to much stronger odd harmonics than even harmonics, as seen in Fig. 3c, while the application of the 500 mm local length lens for the focusing of driving radiation in to the plasma increased the intensity of the even harmonics (Fig. 3d). Application of shorter focal length lens increased the intensity of second harmonic field in the plasma area, and at the same time decreased the overlapping of two beams in the plasma area thus decreasing the influence on the overall dynamics of two-color field HHG.

 

Fig. 3 (a) Harmonic spectra from Ag plasma using the two-color pump configuration. (b) Optimization of even harmonics with regard to the odd ones in the cutoff region. (c) Harmonic spectra using 200 mm focal length focusing mirror. (d) Harmonics spectra using the 500 mm focal length lens.

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An interesting feature of the spectrum in Fig. 3a is the enhanced even (20th) harmonic compared with neighboring even harmonics, although this enhancement (2×) was not as pronounced as those previously reported in studies of single odd harmonics from some plasmas [17]. No spectral line was identified from the NIST tables in this part of the spectrum, but the behavior was similar to resonance enhancements in other metal plasmas. One can note that this ionic line appeared along with harmonic spectra at stronger excitation of silver target.

The resonance-induced growth of a single even harmonic motivated us to search for improvement of harmonic yield in two additional media, chromium and vanadium, which have already displayed enhanced properties using low pulse repetition rate (10 Hz), narrowband (10 nm) laser sources [40,41].

We identified two regimes for HHG in chromium plasma displaying different spectral features. For a weak excitation of the target, a cutoff was observed at 31.2 nm (E = 39.74 eV, 25H). With increased target excitation and increased femtosecond pulse intensity inside the plume by moving the plasma towards the focus of 780 nm radiation, a second plateau appeared with strong 27th and 29th harmonics, and the cutoff was extended toward the range of E = 58.81 eV (37th harmonic). For zero-chirp the 27th and 29th harmonics were approximately equal in intensity. Varying the laser chirp changed the relative intensities of these two harmonics, while the intensities of the other harmonics remained approximately the same. As the chirp was varied and the pulse duration vas changed from +114 fs to −92 fs, the intensity of 27th harmonic considerably increased (15×), while the 29th harmonic became weaker, as seen in Fig. 4a . This is because the 27th harmonic (λ = 28.88 nm, E = 42.91 eV for zero-chirp) is shifted towards the ionic resonance. The presence of such a resonance is confirmed by over-exciting the chromium plasma; the ionic line can be seen at the blue side of 27th harmonic on Fig. 4b.

 

Fig. 4 (a) Harmonic spectra from chromium plasma at different chirps of laser radiation. Positive and negative values of pulse duration correspond to positively and negatively chirped pulses. (b) Harmonic spectrum at over-excited conditions of Cr plasma formation, with ionic lines appearing close to the enhanced 27th and 29th harmonics. The arrow shows one of these lines close to the 27th harmonic.

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The meaning of “weak” excitation stays for intensity of heating pulse on the target surface below 1×1010 W cm−2. In that case, chromium plasma emission shows only spectral lines from excited neutrals and singly charged ions. With increase of intensity (≈2×1010 W cm−2 - 3×1010 W cm−2), the doubly charged ions appear in the plasma plume, which led to their involvement in harmonic generation. Over-excitation of plasma at these conditions means even stronger heating of target when high concentration of free electrons appearing during laser ablation causes the phase mismatching of HHG.

These results are consistent with other HHG studies in Cr plasma, which also displayed a variation in the 27th harmonic intensity for different chirps [40]. In those studies, the 27th harmonic almost disappeared from the harmonic spectra, and a strong 29th harmonic was observed for zero-chirp. The experiments in [40] were performed using 800 nm laser pulses, so the 29th harmonic was closest to the resonance.

Calculated gf values at photon energies range of 40–60 eV (λ = 20.66 – 31 nm) clearly show a group of transitions from 44.5 to 44.8 eV with very strong oscillator strengths (gf between 1 and 2.2; the gf value is the product of the oscillator strength f of a transition and the statistical weight g of the lower level.) [42]. These transitions are much stronger than those in the range of 40 – 60 nm, and are likely to be responsible for the enhancement of the 27th and 29th harmonics we observed in our experiments. Furthermore, strong photoabsorption lines within the 41–42 eV region reported in [42] could decrease the yield of the 25th harmonic.

Two-color pumping revealed that the resonance ionic line similarly impacts the efficiency of even harmonic generation. Figure 5a shows that even harmonics between the 24th and 26th orders (38.15 – 41.33 eV) almost disappeared when chirp-free pulses were used, while the 28th harmonic (44.50 eV) was much stronger (5×) than the lowest order harmonics and almost equal in intensity to the enhanced odd ones. The efficiency with which some high harmonics were generated was two times greater for two-color pumping than for single-color pumping, as seen in Figs. 5a and 5b in the case of the 15th to 17th harmonics. The removal of crystal led to the spectral distribution presented in Fig. 5b, which is similar to Fig. 4b, excluding the stronger 27th harmonic compared with 29th one. This was related with better resonance-induced enhancement of 27th harmonic in the former case.

 

Fig. 5 (a) Two-color pump-induced spectra of harmonics from Cr plasma and (b) the spectra obtained at analogous experimental conditions by removing the SH crystal from the path of 780 nm radiation.

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Finally, we present the results of HHG studies using vanadium plasma. In previous studies, the conversion efficiency in the plateau range of the harmonics of 800 nm radiation was 1.6×10−7 [41]. Those plasma emission spectra measurements and calculations of the ionization conditions and harmonic cutoffs in the laser-ablation plume showed that the higher harmonics originated from the interaction of the femtosecond laser pulses with doubly charged vanadium ions, which allowed generation of harmonics up to the 71st order.

In our case, the dynamics of vanadium harmonics variations was the same as in the case of chromium plasma once the chirp and corresponding redistribution of laser spectrum along the pulse caused the tuning of harmonic wavelength. Only low-order harmonics (up to the 23rd order) were obtained when the V target was weakly excited (Ips = 6×109 W cm−2, Fig. 6a ). With a stronger excitation (Ips = 1×1010 W cm−2), the spectrum extended to higher energies, with the appearance of a “second plateau” beginning with a strong 27th harmonic, as shown in Fig. 6b. Two-color pumping led to an increase in the harmonic yield (Fig. 6c), accompanied by the appearance of an enhanced (4×) 26th harmonic (λ = 30 nm, E = 41.33 eV), which is attributed to the influence of a strong ionic transition at this energy. The background that appears in spectra of Fig. 6 is induced by a scattering from some stray light, which appeared from case to case during different alignments of our registration system.

 

Fig. 6 Variations of harmonic spectra at (a) weak excitation of V target (Ips = 6×109 W cm−2), (b) stronger excitation of target (Ips = 1×1010 W cm−2), and (c) application of two-color pump.

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We have not yet identified the ionic transition responsible for this enhancement. The NIST database contains one relatively strong transition (3p63d - 3p5(2P°)3d2(1G); λ = 31.2 nm) in this spectral region for quadruply ionized vanadium, but it is unlikely that such a high level of ionization was achieved using our laser ablation parameters.

5. Discussion and conclusions

Our two-color HHG studies confirm previously reported spectral features in the vicinity of the 3p - 3d transitions of the Cr II ions [40] and reveal a strong even harmonic generated close to those transitions. The observed enhancement of the 28th harmonic of the 780 nm pump (corresponding to the 14th harmonic of 390 nm radiation) is attributed to the influence of these transitions, although it is not as pronounced compared with the 29th harmonic of 800 nm radiation. The enhancement of the 27th and 28th harmonics from vanadium plasma can also be attributed to an overlap with ionic transitions. Although we were unable to identify these ionic transitions, the ionic lines were seen by over-exciting the target.

Calculations of harmonic enhancement for some plasmas, in particular for the chromium ion, can be found in [10,11]. The coincidence of the enhanced harmonics observed in our experiments with the giant 3p - 3d resonance implies the involvement of this transition in the enhancement. The resonant enhancement can also be considered from a macroscopic perspective. At resonance conditions, when the harmonic frequency is close to the atomic transition frequency, the variation in the wave number of a single harmonic could be large, and the influence of dispersion from free-electrons can be compensated by the atomic dispersion for a specific harmonic order [9]. In this case, improvement of the phase matching conditions for single harmonic can be achieved.

The target survived during multiple shots, without considerable modification of the surface. We constantly moved the target up and down, thus returning back to the same ablated area during multiple movements of the target. It follows that, once the ablation area stays at the same spot of target, the target surface became overheated, which can lead to the change of ablation conditions. When we moved the target by heating different spots, previous ablated areas cooled and returned to the initial conditions. This followed with the same HHG conversion efficiency once we return for ablation to the previously ablated spot. The rotation of targets could considerably improve the stability of plasma harmonics.

We would like to emphasize the importance of using high pulse repetition rate lasers for improving the average power of harmonics, which could be additionally enhanced in the presence of resonance effects and two-color field induced enhancement. This is a main motivation of present work and has been demonstrated for the first time.

From the point of view of optical technology where the average power of the XUV radiation may be critical the demonstration at a 1kHz is essential. So not only does the result ratify earlier findings but it paves the way to concrete applications. Some estimations show that, once usual non-resonant conversion efficiency is of order of ~10−6, with resonance this may be increased by an order of magnitude or higher (~10−5). So for a mJ class laser we expect at least 10nJ per pulse i.e. average power 10 microwatts of XUV at 1kHz, but only 0.1 microwatt at 10Hz. Present work is a further advancement in this field, which shows considerable improvement of the characteristics of plasma harmonics compared with results presented in [31].

In conclusion, we have studied HHG from laser-produced plasmas using three recently introduced techniques to improve the plasma harmonic yield: resonance-induced and two-color pump-induced enhancement, together with the application of a high repetition rate laser source. Together with an increased HHG output, we observed an enhanced yield of even harmonics compared with odd ones, and resonance-induced enhancement in the intensity of some single even harmonics when the ratio between the 780 and 390 nm pulse energies was 25:1.

Our novel high repetition rate source for resonance- and two-color-induced plasma HHG improved the average power of the emitted XUV radiation by two orders of magnitude compared with previous plasma HHG studies using 10 Hz lasers with equal pulse energy. This improvement will be useful both for investigating the temporal characteristics of the high-harmonics from laser plasma and for studying quantum path interference of long and short electron trajectories, both of which require large numbers of laser shots.

During our experiments, several new resonance-enhanced processes were revealed, mostly due to the modification of electron trajectories in HHG by the presence of a weak second harmonic field. This led to the generation of enhanced odd and even harmonics in different regions of the plateau. In particular, we observed an enhanced 20th harmonic in silver plasma (2×), 26th harmonic in vanadium plasma (4×), and 28th harmonic in chromium plasma (5×). These results support theoretical predictions that the involvement of autoionizing states of atoms and ions will enhance nonlinear optical processes in the vicinity of a resonance [9,10]. Crucially, using broadband (40 nm) pulses for plasma HHG permitted tuning of the spectral position of the harmonic comb over a broad range (2.8 nm in the case of 17th harmonic), thus allowing us to ensure that a particular harmonic coincided with the resonance wavelength of an autoionizing state.

Acknowledgments

This research was supported by a Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme and EPSRC programme (grants No. EP/F034601/1, EP/I032517/1, and EP/E028063/1).

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37. D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008). [CrossRef]  

38. I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008). [CrossRef]  

39. R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009). [CrossRef]  

40. R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda, “Harmonic generation from chromium plasma,” Appl. Phys. Lett. 86(13), 131116 (2005). [CrossRef]  

41. M. Suzuki, L. B. Elouga Bom, T. Ozaki, R. A. Ganeev, M. Baba, and H. Kuroda, “Seventy-first harmonic generation from doubly charged ions in preformed laser-ablation vanadium plume at 110 eV,” Opt. Express 15(7), 4112–4117 (2007). [CrossRef]   [PubMed]  

42. C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999). [CrossRef]  

References

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  25. V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
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  29. T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
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  31. R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
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  33. E. Cormier and M. Lewenstein, “Optimizing the efficiency in high order harmonic generation optimization by two-color fields,” Eur. Phys. J. D 12(2), 227–233 (2000).
    [CrossRef]
  34. I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
    [CrossRef]
  35. J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
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  36. T. Pfeifer, L. Gallmann, M. J. Abel, D. M. Neumark, and S. R. Leone, “Single attosecond pulse generation in the multicycle-driver regime by adding a weak second-harmonic field,” Opt. Lett. 31(7), 975–977 (2006).
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  37. D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
    [CrossRef]
  38. I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
    [CrossRef]
  39. R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
    [CrossRef]
  40. R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda, “Harmonic generation from chromium plasma,” Appl. Phys. Lett. 86(13), 131116 (2005).
    [CrossRef]
  41. M. Suzuki, L. B. Elouga Bom, T. Ozaki, R. A. Ganeev, M. Baba, and H. Kuroda, “Seventy-first harmonic generation from doubly charged ions in preformed laser-ablation vanadium plume at 110 eV,” Opt. Express 15(7), 4112–4117 (2007).
    [CrossRef] [PubMed]
  42. C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
    [CrossRef]

2011 (3)

M. Tudorovskaya and M. Lein, “High-order harmonic generation in the presence of a resonance,” Phys. Rev. A 84(1), 013430 (2011).
[CrossRef]

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

L. B. Elouga Bom, S. Haessler, O. Gobert, M. Perdrix, F. Lepetit, J. F. Hergott, B. Carré, T. Ozaki, and P. Salières, “Attosecond emission from chromium plasma,” Opt. Express 19(4), 3677–3685 (2011).
[CrossRef] [PubMed]

2010 (5)

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

V. Strelkov, “Role of autoionizing state in resonant high-order harmonic generation and attosecond pulse production,” Phys. Rev. Lett. 104(12), 123901 (2010).
[CrossRef] [PubMed]

M. V. Frolov, N. L. Manakov, and A. F. Starace, “Potential barrier effects in high-order harmonic generation by transition-metal ions,” Phys. Rev. A 82(2), 023424 (2010).
[CrossRef]

D. B. Milošević, “Resonant high-order harmonic generation from plasma ablation: Laser intensity dependence of the harmonic intensity and phase,” Phys. Rev. A 81(2), 023802 (2010).
[CrossRef]

2009 (3)

R. A. Ganeev, “Generation of high-order harmonics of high-power lasers in plasmas produced under irradiation of solid target surfaces by a prepulse,” Phys. Usp. 52(1), 55–77 (2009).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

I. A. Kulagin and T. Usmanov, “Efficient selection of single high-order harmonic caused by atomic autoionizing state influence,” Opt. Lett. 34(17), 2616–2618 (2009).
[CrossRef] [PubMed]

2008 (2)

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

2007 (6)

R. A. Ganeev, M. Suzuki, P. V. Redkin, M. Baba, and H. Kuroda, “Variable pattern of high-order harmonic spectra from a laser-produced plasma by using the chirped pulses of narrow-bandwidth radiation,” Phys. Rev. A 76(2), 023832 (2007).
[CrossRef]

R. A. Ganeev, “High-order harmonic generation in a laser plasma: a review of recent achievements,” J. Phys. B 40(22), R213–R253 (2007).
[CrossRef]

R. A. Ganeev, L. Bom, J.-C. Kieffer, and T. Ozaki, “Systematic investigation of resonance-induced single-harmonic enhancement in the extreme-ultraviolet range,” Phys. Rev. A 75(6), 063806 (2007).
[CrossRef]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

M. Suzuki, M. Baba, H. Kuroda, R. A. Ganeev, and T. Ozaki, “Intense exact resonance enhancement of single-high-harmonic from an antimony ion by using Ti:Sapphire laser at 37 nm,” Opt. Express 15(3), 1161–1166 (2007).
[CrossRef] [PubMed]

M. Suzuki, L. B. Elouga Bom, T. Ozaki, R. A. Ganeev, M. Baba, and H. Kuroda, “Seventy-first harmonic generation from doubly charged ions in preformed laser-ablation vanadium plume at 110 eV,” Opt. Express 15(7), 4112–4117 (2007).
[CrossRef] [PubMed]

2006 (5)

2005 (3)

R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda, “Harmonic generation from chromium plasma,” Appl. Phys. Lett. 86(13), 131116 (2005).
[CrossRef]

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

2004 (2)

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

D. H. Reitze, S. Kazamias, F. Weihe, G. Mullot, D. Douillet, F. Aug, O. Albert, V. Ramanathan, J. P. Chambaret, D. Hulin, and P. Balcou, “Enhancement of high-order harmonic generation at tuned wavelengths through adaptive control,” Opt. Lett. 29(1), 86–88 (2004).
[CrossRef] [PubMed]

2003 (2)

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
[CrossRef]

2002 (2)

B. Shan, A. Cavalieri, and Z. Chang, “Tunable high harmonic generation with an optical parametric amplifier,” Appl. Phys. B 74(9), s23–s26 (2002).
[CrossRef]

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

2001 (1)

M. B. Gaarde and K. J. Schafer, “Enhancement of many high-order harmonics via a single multiphoton resonance,” Phys. Rev. A 64(1), 013820 (2001).
[CrossRef]

2000 (2)

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

E. Cormier and M. Lewenstein, “Optimizing the efficiency in high order harmonic generation optimization by two-color fields,” Eur. Phys. J. D 12(2), 227–233 (2000).
[CrossRef]

1999 (2)

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

1998 (2)

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

C. Iaconis and I. A. Walmsley, “Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses,” Opt. Lett. 23(10), 792–794 (1998).
[CrossRef] [PubMed]

1993 (1)

P. B. Corkum, “Plasma perspective on strong field multiphoton ionization,” Phys. Rev. Lett. 71(13), 1994–1997 (1993).
[CrossRef] [PubMed]

1992 (1)

J. L. Krause, K. J. Schafer, and K. C. Kulander, “High-order harmonic generation from atoms and ions in the high intensity regime,” Phys. Rev. Lett. 68(24), 3535–3538 (1992).
[CrossRef] [PubMed]

Abel, M. J.

Albert, O.

Antoine, P.

E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

Arpin, P.

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

Aug, F.

Baba, M.

Backus, S.

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Balcou, P.

Bartels, R.

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Baumberg, J. J.

Benis, E. P.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Bohan, A.

E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

Bom, L.

R. A. Ganeev, L. Bom, J.-C. Kieffer, and T. Ozaki, “Systematic investigation of resonance-induced single-harmonic enhancement in the extreme-ultraviolet range,” Phys. Rev. A 75(6), 063806 (2007).
[CrossRef]

Brocklesby, W. S.

Carré, B.

Cavalieri, A.

B. Shan, A. Cavalieri, and Z. Chang, “Tunable high harmonic generation with an optical parametric amplifier,” Appl. Phys. B 74(9), s23–s26 (2002).
[CrossRef]

Chakera, J. A.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

Chambaret, J. P.

Chang, Z.

B. Shan, A. Cavalieri, and Z. Chang, “Tunable high harmonic generation with an optical parametric amplifier,” Appl. Phys. B 74(9), s23–s26 (2002).
[CrossRef]

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

Charalambidis, D.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Chen, M.-C.

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
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Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

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I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

Choi, I.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

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Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

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R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
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E. Cormier and M. Lewenstein, “Optimizing the efficiency in high order harmonic generation optimization by two-color fields,” Eur. Phys. J. D 12(2), 227–233 (2000).
[CrossRef]

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C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
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M. V. Frolov, N. L. Manakov, and A. F. Starace, “Potential barrier effects in high-order harmonic generation by transition-metal ions,” Phys. Rev. A 82(2), 023424 (2010).
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Gaarde, M. B.

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
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Ganeev, R.

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R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
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R. A. Ganeev, “Generation of high-order harmonics of high-power lasers in plasmas produced under irradiation of solid target surfaces by a prepulse,” Phys. Usp. 52(1), 55–77 (2009).
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R. A. Ganeev, L. Bom, J.-C. Kieffer, and T. Ozaki, “Systematic investigation of resonance-induced single-harmonic enhancement in the extreme-ultraviolet range,” Phys. Rev. A 75(6), 063806 (2007).
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R. A. Ganeev, M. Suzuki, P. V. Redkin, M. Baba, and H. Kuroda, “Variable pattern of high-order harmonic spectra from a laser-produced plasma by using the chirped pulses of narrow-bandwidth radiation,” Phys. Rev. A 76(2), 023832 (2007).
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R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

M. Suzuki, M. Baba, H. Kuroda, R. A. Ganeev, and T. Ozaki, “Intense exact resonance enhancement of single-high-harmonic from an antimony ion by using Ti:Sapphire laser at 37 nm,” Opt. Express 15(3), 1161–1166 (2007).
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M. Suzuki, L. B. Elouga Bom, T. Ozaki, R. A. Ganeev, M. Baba, and H. Kuroda, “Seventy-first harmonic generation from doubly charged ions in preformed laser-ablation vanadium plume at 110 eV,” Opt. Express 15(7), 4112–4117 (2007).
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R. A. Ganeev, M. Suzuki, M. Baba, H. Kuroda, and T. Ozaki, “Strong resonance enhancement of a single harmonic generated in the extreme ultraviolet range,” Opt. Lett. 31(11), 1699–1701 (2006).
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R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda, “Harmonic generation from chromium plasma,” Appl. Phys. Lett. 86(13), 131116 (2005).
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Gobert, O.

Gupta, P. D.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

Gustafsson, E.

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

Haessler, S.

Hanna, D. C.

Hergott, J. F.

Hong, K. H.

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Hong, K.-H.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

Hulin, D.

Hutchison, C.

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

Iaconis, C.

Jakubczak, K.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

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J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

Kampen, P.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

Kapteyn, H. C.

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

Kazamias, S.

Kennedy, E. T.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

Khan, R. A.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

Kieffer, J.-C.

R. A. Ganeev, L. Bom, J.-C. Kieffer, and T. Ozaki, “Systematic investigation of resonance-induced single-harmonic enhancement in the extreme-ultraviolet range,” Phys. Rev. A 75(6), 063806 (2007).
[CrossRef]

Kim, C. M.

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

Kim, H.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

Kim, H. T.

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Kim, I. J.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

Kim, J. H.

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Kim, J.-H.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

Kim, T. K.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
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J. L. Krause, K. J. Schafer, and K. C. Kulander, “High-order harmonic generation from atoms and ions in the high intensity regime,” Phys. Rev. Lett. 68(24), 3535–3538 (1992).
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R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
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I. A. Kulagin and T. Usmanov, “Efficient selection of single high-order harmonic caused by atomic autoionizing state influence,” Opt. Lett. 34(17), 2616–2618 (2009).
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J. L. Krause, K. J. Schafer, and K. C. Kulander, “High-order harmonic generation from atoms and ions in the high intensity regime,” Phys. Rev. Lett. 68(24), 3535–3538 (1992).
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Kuroda, H.

L’Huillier, A.

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

Lee, D.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

Lee, D. G.

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Lee, G. H.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

Lee, Y. S.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

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M. Tudorovskaya and M. Lein, “High-order harmonic generation in the presence of a resonance,” Phys. Rev. A 84(1), 013430 (2011).
[CrossRef]

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Lepetit, F.

Lewenstein, M.

E. Cormier and M. Lewenstein, “Optimizing the efficiency in high order harmonic generation optimization by two-color fields,” Eur. Phys. J. D 12(2), 227–233 (2000).
[CrossRef]

Li, R.

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

López-Arias, M. E.

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

Manakov, N. L.

M. V. Frolov, N. L. Manakov, and A. F. Starace, “Potential barrier effects in high-order harmonic generation by transition-metal ions,” Phys. Rev. A 82(2), 023424 (2010).
[CrossRef]

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R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
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Marangos, J. P.

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

Maravelias, G.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
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Martins, M.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

Mauritsson, J.

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

McGuinness, C.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

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D. B. Milošević, “Resonant high-order harmonic generation from plasma ablation: Laser intensity dependence of the harmonic intensity and phase,” Phys. Rev. A 81(2), 023802 (2010).
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Misoguti, L.

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Mocek, T.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

Mosnier, J.-P.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

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E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

Mullot, G.

Murnane, M. M.

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

Naik, P. A.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

Nam, C.

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

Nam, C. H.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Neumark, D. M.

Nikolopoulos, L A A.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Ozaki, T.

Park, J. Y.

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

Park, S. B.

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

Peralta Conde, A.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Perdrix, M.

Pfeifer, T.

Popmintchev, T.

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

Praeger, M.

Ramanathan, V.

Redkin, P. V.

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. A. Ganeev, M. Suzuki, P. V. Redkin, M. Baba, and H. Kuroda, “Variable pattern of high-order harmonic spectra from a laser-produced plasma by using the chirped pulses of narrow-bandwidth radiation,” Phys. Rev. A 76(2), 023832 (2007).
[CrossRef]

Reitze, D. H.

Rogers, E. T. F.

Rundquist, A.

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

Salières, P.

Schafer, K. J.

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

M. B. Gaarde and K. J. Schafer, “Enhancement of many high-order harmonics via a single multiphoton resonance,” Phys. Rev. A 64(1), 013820 (2001).
[CrossRef]

J. L. Krause, K. J. Schafer, and K. C. Kulander, “High-order harmonic generation from atoms and ions in the high intensity regime,” Phys. Rev. Lett. 68(24), 3535–3538 (1992).
[CrossRef] [PubMed]

Shan, B.

B. Shan, A. Cavalieri, and Z. Chang, “Tunable high harmonic generation with an optical parametric amplifier,” Appl. Phys. B 74(9), s23–s26 (2002).
[CrossRef]

Siegel, T.

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

Singhal, H.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

Skantzakis, E.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Sonntag, B. F.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

Starace, A. F.

M. V. Frolov, N. L. Manakov, and A. F. Starace, “Potential barrier effects in high-order harmonic generation by transition-metal ions,” Phys. Rev. A 82(2), 023424 (2010).
[CrossRef]

Strelkov, V.

V. Strelkov, “Role of autoionizing state in resonant high-order harmonic generation and attosecond pulse production,” Phys. Rev. Lett. 104(12), 123901 (2010).
[CrossRef] [PubMed]

Suzuki, M.

Taïeb, R.

R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
[CrossRef]

Tayyab, M.

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

Toma, E. S.

E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

Tosa, V.

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

Tsakiris, G. D.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Tudorovskaya, M.

M. Tudorovskaya and M. Lein, “High-order harmonic generation in the presence of a resonance,” Phys. Rev. A 84(1), 013430 (2011).
[CrossRef]

Tzallas, P.

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Usmanov, T.

Vdovin, G.

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Veniard, V.

R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
[CrossRef]

Vora, H. S.

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

Walmsley, I. A.

Wang, H.

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

Wassaf, J.

R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
[CrossRef]

Weihe, F.

Wernet, P.

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

Xu, Z.

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

Yu, W.

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

Zaïr, A.

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

Zeek, E.

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

Zeng, Z.

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

Appl. Phys. B (1)

B. Shan, A. Cavalieri, and Z. Chang, “Tunable high harmonic generation with an optical parametric amplifier,” Appl. Phys. B 74(9), s23–s26 (2002).
[CrossRef]

Appl. Phys. Lett. (2)

I. J. Kim, G. H. Lee, S. B. Park, Y. S. Lee, T. K. Kim, C. H. Nam, T. Mocek, and K. Jakubczak, “Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field,” Appl. Phys. Lett. 92(2), 021125 (2008).
[CrossRef]

R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda, “Harmonic generation from chromium plasma,” Appl. Phys. Lett. 86(13), 131116 (2005).
[CrossRef]

Eur. Phys. J. D (1)

E. Cormier and M. Lewenstein, “Optimizing the efficiency in high order harmonic generation optimization by two-color fields,” Eur. Phys. J. D 12(2), 227–233 (2000).
[CrossRef]

J. Mod. Opt. (1)

R. A. Ganeev, C. Hutchison, T. Siegel, M. E. López-Arias, A. Zaïr, and J. P. Marangos, “High-order harmonic generation from metal plasmas using 1 kHz laser pulses,” J. Mod. Opt. 58(10), 819–824 (2011).
[CrossRef]

J. Phys. B (3)

C. McGuinness, M. Martins, P. Wernet, B. F. Sonntag, P. Kampen, J.-P. Mosnier, E. T. Kennedy, and J. T. Costello, “Metastable state contributions to the measured 3p photoabsorption spectrum of Cr+ ions in a laser-produced plasma,” J. Phys. B 32(20), L583–L591 (1999).
[CrossRef]

R. A. Ganeev, “High-order harmonic generation in a laser plasma: a review of recent achievements,” J. Phys. B 40(22), R213–R253 (2007).
[CrossRef]

E. S. Toma, P. Antoine, A. Bohan, and H. G. Muller, “Resonance-enhanced high-harmonic generation,” J. Phys. B 32(24), 5843–5852 (1999).
[CrossRef]

Nat. Photonics (1)

T. Popmintchev, M.-C. Chen, P. Arpin, M. M. Murnane, and H. C. Kapteyn, “The attosecond nonlinear optics of bright coherent X-ray generation,” Nat. Photonics 4(12), 822–832 (2010).
[CrossRef]

Nature (1)

R. Bartels, S. Backus, E. Zeek, L. Misoguti, G. Vdovin, I. P. Christov, M. M. Murnane, and H. C. Kapteyn, “Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays,” Nature 406(6792), 164–166 (2000).
[CrossRef] [PubMed]

New J. Phys. (1)

D. Charalambidis, P. Tzallas, E. P. Benis, E. Skantzakis, G. Maravelias, L A A. Nikolopoulos, A. Peralta Conde, and G. D. Tsakiris, “Exploring intense attosecond pulses,” New J. Phys. 10(2), 025018 (2008).
[CrossRef]

Opt. Express (3)

Opt. Lett. (8)

I. A. Kulagin and T. Usmanov, “Efficient selection of single high-order harmonic caused by atomic autoionizing state influence,” Opt. Lett. 34(17), 2616–2618 (2009).
[CrossRef] [PubMed]

C. Iaconis and I. A. Walmsley, “Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses,” Opt. Lett. 23(10), 792–794 (1998).
[CrossRef] [PubMed]

D. H. Reitze, S. Kazamias, F. Weihe, G. Mullot, D. Douillet, F. Aug, O. Albert, V. Ramanathan, J. P. Chambaret, D. Hulin, and P. Balcou, “Enhancement of high-order harmonic generation at tuned wavelengths through adaptive control,” Opt. Lett. 29(1), 86–88 (2004).
[CrossRef] [PubMed]

C. A. Froud, E. T. F. Rogers, D. C. Hanna, W. S. Brocklesby, M. Praeger, A. M. de Paula, J. J. Baumberg, and J. G. Frey, “Soft-x-ray wavelength shift induced by ionization effects in a capillary,” Opt. Lett. 31(3), 374–376 (2006).
[CrossRef] [PubMed]

T. Pfeifer, L. Gallmann, M. J. Abel, D. M. Neumark, and S. R. Leone, “Single attosecond pulse generation in the multicycle-driver regime by adding a weak second-harmonic field,” Opt. Lett. 31(7), 975–977 (2006).
[CrossRef] [PubMed]

R. A. Ganeev, M. Suzuki, M. Baba, H. Kuroda, and T. Ozaki, “Strong resonance enhancement of a single harmonic generated in the extreme ultraviolet range,” Opt. Lett. 31(11), 1699–1701 (2006).
[CrossRef] [PubMed]

M. Suzuki, M. Baba, R. Ganeev, H. Kuroda, and T. Ozaki, “Anomalous enhancement of a single high-order harmonic by using a laser-ablation tin plume at 47 nm,” Opt. Lett. 31(22), 3306–3308 (2006).
[CrossRef] [PubMed]

R. A. Ganeev, P. A. Naik, H. Singhal, J. A. Chakera, and P. D. Gupta, “Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas,” Opt. Lett. 32(1), 65–67 (2007).
[CrossRef] [PubMed]

Phys. Rev. A (13)

R. A. Ganeev, M. Suzuki, P. V. Redkin, M. Baba, and H. Kuroda, “Variable pattern of high-order harmonic spectra from a laser-produced plasma by using the chirped pulses of narrow-bandwidth radiation,” Phys. Rev. A 76(2), 023832 (2007).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, I. A. Kulagin, P. V. Redkin, J. A. Chakera, M. Tayyab, R. A. Khan, and P. D. Gupta, “Enhancement of high-order harmonic generation using a two-color pump in plasma plumes,” Phys. Rev. A 80(3), 033845 (2009).
[CrossRef]

R. Taïeb, V. Veniard, J. Wassaf, and A. Maquet, “Roles of resonances and recollisions in strong-field atomic phenomena. II. High-order harmonic generation,” Phys. Rev. A 68(3), 033403 (2003).
[CrossRef]

M. B. Gaarde and K. J. Schafer, “Enhancement of many high-order harmonics via a single multiphoton resonance,” Phys. Rev. A 64(1), 013820 (2001).
[CrossRef]

M. V. Frolov, N. L. Manakov, and A. F. Starace, “Potential barrier effects in high-order harmonic generation by transition-metal ions,” Phys. Rev. A 82(2), 023424 (2010).
[CrossRef]

D. B. Milošević, “Resonant high-order harmonic generation from plasma ablation: Laser intensity dependence of the harmonic intensity and phase,” Phys. Rev. A 81(2), 023802 (2010).
[CrossRef]

M. Tudorovskaya and M. Lein, “High-order harmonic generation in the presence of a resonance,” Phys. Rev. A 84(1), 013430 (2011).
[CrossRef]

R. A. Ganeev, H. Singhal, P. A. Naik, J. A. Chakera, H. S. Vora, R. A. Khan, and P. D. Gupta, “Systematic studies of two-color pump-induced high-order harmonic generation in plasma plumes,” Phys. Rev. A 82(5), 053831 (2010).
[CrossRef]

Z. Chang, A. Rundquist, H. Wang, I. Christov, H. C. Kapteyn, and M. M. Murnane, “Temporal phase control of soft-x-ray harmonic emission,” Phys. Rev. A 58(1), R30–R33 (1998).
[CrossRef]

H. T. Kim, J. H. Kim, D. G. Lee, K. H. Hong, Y. S. Lee, V. Tosa, and C. H. Nam, “Optimization of high-order harmonic brightness in the space and time domains,” Phys. Rev. A 69(3), 031805 (2004).
[CrossRef]

R. A. Ganeev, L. Bom, J.-C. Kieffer, and T. Ozaki, “Systematic investigation of resonance-induced single-harmonic enhancement in the extreme-ultraviolet range,” Phys. Rev. A 75(6), 063806 (2007).
[CrossRef]

H. Kim, D. Lee, K.-H. Hong, J.-H. Kim, I. Choi, and C. Nam, “Continuously tunable high-order harmonics from atoms in an intense femtosecond laser field,” Phys. Rev. A 67(5), 051801 (2003).
[CrossRef]

V. Tosa, H. T. Kim, I. J. Kim, and C. H. Nam, “High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis,” Phys. Rev. A 71(6), 063808 (2005).
[CrossRef]

Phys. Rev. Lett. (5)

J. L. Krause, K. J. Schafer, and K. C. Kulander, “High-order harmonic generation from atoms and ions in the high intensity regime,” Phys. Rev. Lett. 68(24), 3535–3538 (1992).
[CrossRef] [PubMed]

P. B. Corkum, “Plasma perspective on strong field multiphoton ionization,” Phys. Rev. Lett. 71(13), 1994–1997 (1993).
[CrossRef] [PubMed]

V. Strelkov, “Role of autoionizing state in resonant high-order harmonic generation and attosecond pulse production,” Phys. Rev. Lett. 104(12), 123901 (2010).
[CrossRef] [PubMed]

I. J. Kim, C. M. Kim, H. T. Kim, G. H. Lee, Y. S. Lee, J. Y. Park, D. J. Cho, and C. H. Nam, “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94(24), 243901 (2005).
[CrossRef]

J. Mauritsson, P. Johnsson, E. Gustafsson, A. L’Huillier, K. J. Schafer, and M. B. Gaarde, “Attosecond pulse trains generated using two color laser fields,” Phys. Rev. Lett. 97(1), 013001 (2006).
[CrossRef] [PubMed]

Phys. Scr. (1)

Z. Zeng, R. Li, Y. Cheng, W. Yu, and Z. Xu, “Resonance-enhanced high-order harmonic generation and frequency mixing in two-color laser field,” Phys. Scr. 66(4), 321–325 (2002).
[CrossRef]

Phys. Usp. (1)

R. A. Ganeev, “Generation of high-order harmonics of high-power lasers in plasmas produced under irradiation of solid target surfaces by a prepulse,” Phys. Usp. 52(1), 55–77 (2009).
[CrossRef]

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Figures (6)

Fig. 1
Fig. 1

Experimental setup: HPP, heating pump pulse; FPP, femtosecond probe pulse; M, mirrors; VC, vacuum chamber; T, target; FM, focusing mirror; FFG, flat field grating; MCP, microchannel plate; CCD, charge coupled device.

Fig. 2
Fig. 2

Harmonic spectra from Ag plasma in the cases of (a) apertureless and (b) apertured single color pump (780 nm). (c) Tuning of 17th and 19th harmonics by changing the distance between the gratings in the compressor stage. Positive and negative values of pulse duration correspond to positively and negatively chirped pulses. Dotted lines show the tuning of 17th and 19th harmonics with different chirps. Black lines show the wavelengths of these harmonics at chirp-free conditions. Thick black lines on the left side of bottom graph show the tuning range of 17th harmonic (2.8 nm).

Fig. 3
Fig. 3

(a) Harmonic spectra from Ag plasma using the two-color pump configuration. (b) Optimization of even harmonics with regard to the odd ones in the cutoff region. (c) Harmonic spectra using 200 mm focal length focusing mirror. (d) Harmonics spectra using the 500 mm focal length lens.

Fig. 4
Fig. 4

(a) Harmonic spectra from chromium plasma at different chirps of laser radiation. Positive and negative values of pulse duration correspond to positively and negatively chirped pulses. (b) Harmonic spectrum at over-excited conditions of Cr plasma formation, with ionic lines appearing close to the enhanced 27th and 29th harmonics. The arrow shows one of these lines close to the 27th harmonic.

Fig. 5
Fig. 5

(a) Two-color pump-induced spectra of harmonics from Cr plasma and (b) the spectra obtained at analogous experimental conditions by removing the SH crystal from the path of 780 nm radiation.

Fig. 6
Fig. 6

Variations of harmonic spectra at (a) weak excitation of V target (Ips = 6×109 W cm−2), (b) stronger excitation of target (Ips = 1×1010 W cm−2), and (c) application of two-color pump.

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