Open Access
Add to BibSonomy
Abstract
We report the generation of high-repetition-rate picosecond pulses in the 1.3-1.5 µm spectral range by internal second harmonic generation (SHG) of an idler-resonant optical parametric oscillator (OPO) based on MgO-doped periodically-poled LiNbO3 (MgO:PPLN), synchronously pumped by ∼20 ps pulses at 80 MHz using an Yb-fiber laser at 1.064 µm. By taking advantage of the high spatial quality of the resonant idler beam in the 2503-3030 nm wavelength range and using a second MgO:PPLN crystal with fanout grating structure for intracavity SHG, we have achieved spectral coverage across 1272-1515 nm with up to 1.23 W average power. The second harmonic output exhibits a power stability of 3% rms over 1 hour in pulses of 8.3 ps with Gaussian beam profile. The described approach overcomes the spectral limitation of 1.064 µm-pumped OPOs based on MgO:PPLN and other oxide-based nonlinear crystals, where signal generation below ∼1.45 µm is precluded by multi-phonon absorption of idler radiation above ∼4 µm.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
High-average-power, high-repetition-rate, picosecond optical parametric oscillators (OPOs) in the mid-infrared (mid-IR) based on quasi-phase-matched (QPM) crystal of MgO-doped periodically-poled LiNbO3 (MgO:PPLN) pumped at 1.064 µm are of great interest for variety of applications in physics [1], chemistry [2], biology and medical sciences [3]. By harnessing the high nonlinearity (deff∼16 pm/V) and long interaction lengths (∼50 mm) in MgO:PPLN, such OPOs can conveniently provide tunable radiation from ∼1.45 µm to ∼4 µm in the mid-IR at multi-Watt output power levels with excellent photon conversion efficiency [4]. However, while OPOs based on MgO:PPLN are now very mature and well-established technology in all temporal domains from continuous-wave [5] to femtosecond [6] time-scales, access to the ∼1.1-1.45 µm regions with direct pumping at 1.064 µm is precluded by strong multi-phonon absorption at idler wavelengths near the mid-IR transparency cut-off of MgO:PPLN, where the material exhibits an absorption coefficient of ∼0.08 cm-1 at 4 µm, rapidly increasing to 0.94 cm-1 at 5 µm [7]. Due to the strong absorption of the mid-IR idler wave beyond ∼4 µm, the photon conversion efficiency for the signal wave is drastically reduced, either ceasing OPO operation and/or leading to catastrophic damage to the crystal [8], thereby preventing direct access to signal wavelengths below ∼1.45 µm. The same fundamental limitation also applies to all other oxide-based QPM nonlinear crystals such as periodically-poled KTiOPO4 (PPKTP), KTiOAsO4 (PPKTA), RbTiOAsO4 (PPRTA), and LiTaO3 (PPLT), and their birefringent counterparts.
An alternative approach to access the wavelength range of ∼1.1-1.45 µm is to deploy green-pumped OPOs using the second harmonic of Yb-fiber or solid-state laser at 532 nm as the input pump source, thus providing idler radiation from ∼1.1 μm to ∼4 μm [9–11]. However, this approach suffers from the major drawback of photorefractive damage and green-induced infrared absorption (GRIIRA) in MgO:PPLN, which hampers OPO operation at moderate green pump powers, thus limiting practical output powers from the device [12,13]. More critically, photorefractive effect and GRIIRA result in degradation of spatial beam quality, and thermal loading and lensing in the crystal, leading to high OPO output instability, and ultimately catastrophic crystal damage [11,12]. Operation of such a green-pumped picosecond OPO based on MgO:PPLN has been previously reported by deploying a frequency-doubled, Yb-fiber-amplified gain-switched laser diode as the pump source [11]. The OPO could provide tuning coverage in the idler across the 1.28-1.54 µm spectral range, but oscillation could not be sustained for more than ∼30 minutes due to bulk damage to the MgO:PPLN crystal. The exploitation of other QPM materials such as MgO-doped stoichiometric periodically-poled LiTaO3 (MgO:sPPLT) and PPKTP for green-pumping could potentially provide an alternative solution to tunable generation in the ∼1.1-1.45 μm spectral range. Both crystals offer a moderate nonlinear coefficient, deff∼9 pm/V in MgO:sPPLT and deff∼10 pm/V in PPKTP, and have deeper transparency cut-off in the ultraviolet [14,15]. We have previously demonstrated operation of green-pumped picosecond OPOs based on MgO:sPPLT [10,12] and PPKTP [9] using the second harmonic of an Yb-fiber laser at 532 nm as the pump source. However, despite increased resistance to green pumping compared to MgO:PPLN, the performance of both crystals remains hindered by residual effects of GRIIRA, thermal lensing, photorefractive damage, and two-photon absorption [9,12]. Moreover, in contrast to MgO:PPLN, which offers mature growth and poling technology and widespread commercial availability in long interaction lengths (up to ∼80 mm), MgO:sPPLT and PPKTP suffer from very restricted availability, high cost, limited sample lengths (<30 mm), as well as increasing challenges in fabricating crystals with sufficiently short grating period for green pumping under 1st-order QPM interaction. Operation of green-pumped picosecond OPOs exploiting more traditional birefringent nonlinear crystal of LiB3O5 has also been previously reported [16], but the low nonlinearity of this material (deff ∼1 pm/V) and limited interaction length (<30 mm) result in very limited output powers. Table 1 provides a chronological summary of high-repetition-rate picosecond OPOs providing wavelength coverage in the ∼1.1-1.5 μm spectral range developed to date. As evident, all such OPOs deploy Ti:sapphire or green pump sources to provide the required wavelength coverage. The red and blue shaded regions correspond to OPOs pumped by Ti:sapphire and Nd-based solid-state lasers, respectively, while the yellow shaded rows represent OPOs pumped by Yb-fiber-based green sources.
Against this backdrop, it would be desirable to devise alternative techniques for wavelength generation across the ∼1.1-1.45 μm spectral gap using OPOs, while avoiding the deleterious effects of green pumping in MgO:PPLN and alternative QPM materials, and the need for frequency doubling of fundamental laser at ∼1.064 μm. A potentially viable approach to achieve this goal would be to maintain direct infrared pumping of MgO:PPLN using widely available solid-state and fiber lasers at ∼1.064 μm, but exploit second harmonic generation (SHG) of the mid-IR idler wave in the ∼2.2-4 μm spectral range. This can provide tunable coverage across the entire ∼1.1-1.5 μm spectral gap using widely available MgO:PPLN, while operating the OPO well within the transmission window of the crystal and avoiding multi-phonon idler absorption above ∼4 μm, also circumventing the deleterious effects of GRIIRA and photorefractive damage under green pumping. The approach also offers the advantage of removing the constraints on fabrication of short grating periods over long interaction lengths, as would be necessary for green pumping, since the required QPM periods for SHG of mid-IR idler wave will be similar to or longer than those for the OPO crystal itself. On the other hand, a potential drawback of the technique would be the low SHG conversion efficiency resulting from the relatively poor spatial quality of the non-resonant idler beam generated in a single pass in conventional signal-resonant OPOs. This obstacle can, however, be overcome by deploying an idler-resonant configuration for the OPO to provide the required spatial quality in the idler beam for efficient SHG into the ∼1.1-1.5 μm spectral range. Previously, we demonstrated such an idler-resonant scheme in a picosecond OPO based on MgO:PPLN pumped by an Yb-fiber laser at 1.064 μm, providing high spatial quality with M2<1.8 in the idler beam, providing Watt-level output power and tunability across 2198-4028 nm in the mid-IR [28].
Here, we exploit intracavity SHG of the idler wave from this OPO in a second MgO:PPLN crystal to achieve coverage within the ∼1.1-1.45 μm spectral gap. Moreover, to obtain maximum SHG conversion efficiency, we deploy an intracavity configuration to take advantage of the high circulating idler intensities available internal to the OPO resonator, and in order to minimize internal losses and achieve highest SHG output power in a single pass, we use a ring geometry for the OPO cavity. Using this arrangement, we obtain tuning across 1272-1515 nm, limited only by the available optics, and generate up to 1.23 W average power at 1324 nm, with >1 W over 1298-1373 nm region. The SHG output exhibits excellent passive power stability of 3% rms over 1 hour, in pulses of 8.3 ps with good spatial beam quality in Gaussian profile. The OPO also delivers tunable radiation across 1641-1852 nm in the signal, providing ∼4 W of average output power across the tuning range.
2. Experimental setup
The schematic of the idler-resonant picosecond OPO with intracavity SHG is shown in Fig. 1. The OPO is synchronously pumped by a picosecond Yb-fiber laser operating at a central wavelength of 1064.5 nm with a full-width-at-half-maximum (FWHM) bandwidth of Δλpump∼1 nm, in pulses of ∼20 ps duration at 80 MHz repetition rate. The laser power and polarization are controlled using the combination of two half-wave plates (HWPs) and a polarizing beam-splitter (PBS), after which a maximum average power of ∼10 W is available for pumping the OPO. The nonlinear crystal for the idler-resonant picosecond OPO, C1, is a 50-mm-long, 16-mm-wide and 1-mm-thick 5 mol% MgO:PPLN with a fanout grating period ranging over Λ=26.5-32.5 μm, for type-0 (e→ee) QPM interaction. The end-faces of C1 are antireflection (AR)-coated for the pump, signal, and idler at 1064 nm (R < 1%), 1400-2000 nm (R < 0.5%), and 2000-4000 nm (R < 7%), respectively. Although C1 has a fanout grating structure for tunable signal and idler generation by linear translation the crystal in the picosecond OPO, only part of the crystal is usable. Hence, we use C1 at a fixed grating period and tuning of the picosecond OPO was achieved by changing the temperature of the crystal. The nonlinear crystal for the intracavity SHG of the idler-resonant picosecond OPO, C2, is another 50-mm-long, 10-mm-wide, 1-mm-thick, 5 mol% MgO:PPLN for type-0 (ee→e) QPM interaction, with a fanout grating period ranging over Λ=34.8-36.2 μm. Both C1 and C2 crystals are mounted on two independent ovens providing temperature control for phase-matching from 25°C to 200°C. While C1 is temperature-tuned at a fixed grating period, the optimum phase-matching for intracavity SHG is achieved by grating variation of C2 crystal at constant temperature of 150°C. The picosecond idler-resonant OPO is configured in a ring cavity comprising two pairs of plano-concave folding mirrors forming two intracavity foci and two plane mirrors. The first pair, M1-M2 (r = 200 mm), provide the focus for the OPO gain crystal, C1, while the second pair, M4-M5 (r = 150 mm), are used to focus the resonant idler in the SHG crystal, C2. All mirrors, M1-M5 and M10, are highly reflecting for the idler (R > 99.9% over 2500-4000 nm) and highly transmitting for the pump (T∼92% at 1064 nm) and signal (T > 80% over 1300-2000 nm), thus ensuring singly-resonant oscillation for the mid-IR idler wave along with the direct extraction of the single-pass intracavity idler-SHG through M5. The pump beam is focused to a waist radius of wop∼60 µm at the center of C1, corresponding to a Rayleigh range of ∼46 mm and a focusing parameter of ξ∼1.1. The wide idler wavelength tunability of >520 nm in the mid-IR could significantly affect the idler beam waist in both nonlinear crystals. The intracavity idler beam waist radius estimated from the cavity design calculations indicates a variation from woi1∼93 µm at 2540 nm to woi1∼103 µm at 3030 nm in C1. The corresponding idler beam waist radius in C2 is estimated to vary from woi2∼52 µm at 2540 nm to woi2∼47 µm at 3030 nm, resulting in a nominal change of 5 µm across the tuning range. Additionally, four silver-coated mirrors, M6-M9, with high reflectivity (R > 97%) for the idler form an intracavity delay line enabling precise cavity length control to set the round-trip optical length of the cavity to ∼3.75 m, ensuring synchronization with the pump laser repetition rate. In order to achieve highest idler-SHG efficiency, we maximize the intracavity idler power by using a highly reflecting (R > 99%) plane mirror, M10, to complete the OPO cavity. A dichroic mirror, M, separates the generated signal from the residual pump and a lens, L2, AR-coated for high transmission (T > 97%) over 1650-1900 nm, is used for collimation and characterization of the single-pass signal beam from the picosecond idler-resonant OPO.
Fig. 1. Experimental setup for intracavity SHG of the picosecond idler-resonant OPO pumped by an Yb-fiber laser at 1.064 μm. HWP: Half-wave plate, PBS: Polarizing beam-splitter, L: Lens, C: Crystal, M: Mirrors.
3. Wavelength tuning
Initially, we investigated the wavelength tuning characteristics of the picosecond OPO as well as the intracavity idler-SHG. The variation of the single-pass signal and resonant idler wavelengths as function of temperature for a fixed grating period of Λ=31.34 µm in C1 crystal is shown in Fig. 2(a), while the phase-matched intracavity idler-SHG wavelength as a function on the optimum grating period at fixed C2 crystal temperature of 150°C is shown in Fig. 2(b). The discrete data points correspond to the experimentally measured central wavelength, while the solid lines are the theoretical calculations, confirming good agreement. By changing the temperature of the C1 crystal over 25-200°C, the signal wavelength is tuned across 1641-1852 nm, with the corresponding idler tunable over 2503-3030 nm. On the other hand, the intracavity idler-SHG is tunable across 1272-1515 nm by simple and continuous translation of the C2 crystal. Although the intracavity idler wavelength in the picosecond OPO reaches ∼2500 nm, enabling SHG down to 1250 nm, the extraction of idler-SHG from the OPO cavity is limited by the high reflectivity (R > 99%) of M5 below 1300 nm. Hence, the shortest idler-SHG output wavelength obtained in our experiment is 1272 nm, while the full potential of the picosecond idler-resonant OPO is exploited towards the longer idler-SHG wavelength, reaching up to 1515 nm. It is interesting to note that the overall change in the grating period required for optimal phase-matching of idler-SHG across the demonstrated range is ∼0.7 µm, corresponding to a linear C2 crystal translation of <5 mm. Moreover, it is evident from Fig. 2(b) that the optimal grating period required for phase-matching initially increases with the idler-SHG wavelength up to 1350 nm, beyond which an inflection in the grating period is observed. This behavior of the idler-SHG phase-matching curve results in interesting phenomena, such a ultrawide spectral acceptance bandwidth for SHG at the inflection point, thereby enabling broadband SHG or tunable idler-SHG with minimal crystal translation for grating period optimization. The calculated spectral acceptance bandwidth for SHG together with the phase-mismatch in the C2 crystal corresponding to the required QPM grating period as a function of idler-SHG wavelength is presented in Fig. 2(c). As evident, the phase-mismatch exhibits negligible variation with idler-SHG wavelength, indicating the possibility of broadband SHG in the 1300-1400 nm wavelength range. The exploitation of such broad acceptance bandwidth for idler-SHG is not possible close to room temperature for the available grating periods in the C2 crystal. Hence, we operate C2 well above room temperature at 150 °C.
Fig. 2. (a) Temperature tuning curves for the picosecond idler-resonant OPO for a fixed C1 crystal grating period of Λ=31.34 µm. (b) Variation of the idler-SHG wavelength as a function of the grating period for a fixed C2 crystal temperature of 150°C. (c) Spectral acceptance bandwidth and the corresponding phase-mismatch in C2 crystal as a function of the idler-SHG wavelength.
The spectra across the tuning range of the intracavity SHG and picosecond idler-resonant OPO are shown in Fig. 3. The single-pass signal spectra together with the corresponding FWHM spectral bandwidth at a few representative signal wavelengths are shown in Fig. 3(a). The measured signal spectra exhibit strong features deviating from a smooth single-peak profile. This behavior is attributed to the high intracavity power in the singly-resonant OPO in the absence of output coupling, leading to self-phase-modulation (SPM) of the idler, consequently also impacting the spectral characteristics of the signal. As a result, both the intracavity idler and the single-pass signal exhibit significant spectral modulation. Further, the FWHM bandwidth of the generated signal spectra gradually increase from 8.5 nm at 1641 nm to 28 nm at 1852 nm. Such an increase in signal bandwidth is expected due to the increase in parametric gain bandwidth together with stronger SPM as we approach degeneracy at 2128 nm. The spectra across the idler-SHG tuning range are also presented in Fig. 3(b). The corresponding FWHM spectral bandwidth varies from ∼7.6 nm at 1272 nm to ∼1 nm at 1515 nm with a maximum bandwidth of ∼15 nm measured at a central wavelength of 1365 nm. The large spectral bandwidth generated in this wavelength range is attributed to the broadband intracavity idler spectrum due to SPM in the singly-resonant OPO cavity combined with the ultrawide spectral acceptance bandwidth for SHG, as shown in Fig. 2(c). Given the modulation in the signal and the idler-SHG spectra, the central wavelengths are estimated using a center-of-mass algorithm.
Fig. 3. (a) Single-pass signal and idler-SHG spectra and the corresponding spectral bandwidths across the tuning range.
The average output power across the signal tuning range of the idler-resonant picosecond OPO, obtained by temperature tuning the C1 crystal, for a maximum available pump power of 10 W, recorded after extraction from the residual pump, is presented in Fig. 4(a). The signal power remains close to 4 W across the entire tuning range of 1641-1852 nm, with a maximum of 4.6 W at a central signal wavelength of 1677 nm. Similarly, the average output power across the idler-SHG tuning range, achieved by simultaneously optimizing the grating period of C2 crystal at a fixed temperature of 150°C, is shown in Fig. 4(b). The idler-SHG power varies from 500 mW at 1272 nm to 330 mW at 1515 nm, with a maximum of 1.23 W at 1330 nm and >1 W over 1298-1373 nm wavelength range. From Fig. 4, it can be seen that the picosecond idler-resonant OPO can provide practical output powers over 209 nm in the signal and 243 nm in idler-SHG tunable range.
Fig. 4. Average output power generated across (a) signal, and (b) idler-SHG tuning range of the idler-resonant picosecond OPO.
4. Power scaling and beam quality
The single-pass signal and intracavity idler-SHG power scaling results, while generating maximum idler-SHG power from the picosecond idler-resonant OPO, are presented in Fig. 5. For a maximum available pump power of 10 W, the idler-resonant OPO provides as much as 3.7 W of signal power at 1780 nm together with an idler-SHG power of 1.2 W at 1324 nm. This corresponds to an optical conversion efficiency of 37% for the signal and 12% for idler-SHG wavelength. The corresponding slope efficiencies are estimated to be ∼41% and ∼13% for the signal and idler-SHG. The average power threshold of the idler-resonant OPO is measured to be ∼1 W, while a maximum pump depletion of ∼84% is recorded. Similar values for pump depletion of >70% are recorded at other wavelengths. Also shown in the inset of Fig. 5 is the far-field spatial beam profile of the idler-SHG at 1324 nm, indicating a single-peak Gaussian intensity distribution.
Fig. 5. Power scaling of single-pass signal and idler-SHG extracted from the picosecond idler-resonant OPO. Inset: Far-field spatial beam profile of the idler-SHG beam at 1324 nm.
Fig. 6. Beam quality measurement of (a,b) signal, and (c,d) intracavity idler-SHG, extracted from the picosecond idler-resonant OPO while generating maximum idler-SHG power.
Using a scanning beam profiler and a focusing lens, to determine the beam diameter across the Rayleigh range, we measured the beam quality of the signal and idler-SHG beams, with the results shown in Fig. 6(a) and (b), respectively. The measurements resulted in Mx2<1.9 and My2<1.9 for the signal at 1780nm and Mx2<1.6 and My2<2.3 for the idler-SHG at 1324 nm.
5. Power stability and pulse duration
The simultaneously measured power stability of the single-pass signal and idler-SHG output, while generating maximum idler-SHG power, is presented in Fig. 7(a) and (b), respectively. The extracted signal at a central wavelength of 1780 nm exhibits a passive power stability better than 0.6% rms over 1 hour, while the idler-SHG exhibits a passive stability better than 3% rms over the same period at a central wavelength of 1324 nm. Similar measurement for the pump power resulted in passive stability better than 0.1% rms over 1 hour, as shown in Fig. 7(c).
Fig. 7. Output power stability of (a) signal and (b) idler-SHG from the picosecond idler-resonant OPO, and (c) input pump power stability.
Finally, we performed autocorrelation measurements to determine the temporal characteristics of idler-SHG pulses extracted from the picosecond idler-resonant OPO. The typical interferometric autocorrelation measurement of the idler-SHG beam is shown in Fig. 8, where a Gaussian pulse duration of 8.3 ps is obtained. Also shown in the inset is the idler-SHG spectrum centered at 1392 nm, with a FWHM spectral bandwidth of 2.6 nm. The measured pulse duration and spectral bandwidth result in a time-bandwidth product of ΔτΔυ∼3.3, which is ∼7.5 times that of a transform-limited Gaussian pulse. Further improvements in pulse quality, spectrum, and time-bandwidth product can be achieved by implementing dispersion compensation of the idler-resonant OPO to minimize SPM, while ensuring maximum idler-SHG power by maintaining minimum output coupling.
Fig. 8. Interferometric autocorrelation of the idler-SHG pulses extracted from the picosecond idler-resonant OPO. Inset: Idler-SHG spectrum centered at 1392 nm.
6. Conclusions
In conclusion, we demonstrated a high-average-power, high-repetition-rate, picosecond source based on internal SHG of an idler-resonant OPO pumped at 1064 nm by an Yb-fiber laser and providing tuning coverage across 1272-1515 nm. The source can provide up to 1.2 W of average power in 8.3 ps pulses with M2<2.3 and passive power stability better than 3% rms at 1324 nm. The fanout grating crystal for frequency-doubling enables convenient tuning of SHG across the idler wavelength range using simple mechanical translation of the crystal at a fixed temperature. In addition to idler-SHG, the picosecond OPO provides single-pass signal output tunable over 1641-1852 nm with ∼4 W of average power across the tuning range and excellent passive power stability better than 0.6% rms at 1780 nm. The tunability of the idler-SHG below 1272 nm is limited by low transmission of cavity optics, while the wavelength range beyond 1515 nm can be directly accessed in the signal wavelength range by using a suitable grating period for C1 crystal. By further optimizing the cavity optics it will be possible to extend the tuning range down to ∼1100 nm in the present setup with the available C1 and C2 crystal gratings. By implementing dispersion management of OPO cavity, we will also achieve improvements in spectral and temporal quality of the idler-SHG output pulses as well as enhancement of overall extraction efficiency and output power. We believe internal SHG of an idler-resonant OPO is a viable and practical approach to access the traditionally challenging spectral range of ∼1.1-1.45 μm in oxide-based nonlinear materials under direct pumping at ∼1 µm using widely available Yb-based solid-state and fiber lasers.
Funding
Ministerio de Ciencia y Innovación (PID2020-112700RB-00, CEX2019-000910-S, MCIN/AEI/10.13039/501100011033, RYC2019-027144-I); Fundación Cellex; Fundació Mir-Puig; Generalitat de Catalunya; European Social Fund (Investing in your future, RYC2019-027144-I).
Acknowledgments
S. Chaitanya Kumar acknowledges support through RYC2019-027144-I funded by MCIN/AEI/10.13039/501100011033 and European Social Fund (ESF) “Investing in your future”.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. S. Adachi, T. Oguchi, H. Tanida, S.-Y. Park, H. Shimizu, H. Miyatake, N. Kamiya, Y. Shiro, Y. Inoue, T. Ueki, and T. Iizuka, “The RIKEN structural biology beamline II (BL44B2) at the SPring-8,” Nucl. Instrum. Methods Phys. Res., Sect. A 467-468, 711–714 (2001). [CrossRef]
2. J. Qin, L. Shi, S. Dziennis, R. Reif, and R. K. Wang, “Fast synchronized dual-wavelength laser speckle imaging system for monitoring hemodynamic changes in a stroke mouse model,” Opt. Lett. 37(19), 4005–4007 (2012). [CrossRef]
3. E. O. Potma and X. Sunney Xie, “CARS Microscopy for Biology and Medicine,” Opt. Photonics News 15(11), 40–45 (2004). [CrossRef]
4. M. Ebrahim-Zadeh and S. Chaitanya Kumar, “Yb-fiber-laser-pumped ultrafast frequency conversion sources from the mid-Infrared to the ultraviolet,” IEEE J. Sel. Top. Quantum Electron. 20(5), 624–642 (2014). [CrossRef]
5. M. Ebrahim-Zadeh, S. Chaitanya Kumar, and K. Devi, “Yb-fiber-laser-pumped continuous-wave frequency conversion sources from the mid-infrared to the ultraviolet,” IEEE J. Sel. Top. Quantum Electron. 20(5), 350–372 (2014). [CrossRef]
6. F. Adler, K. C. Cossel, M. J. Thorpe, I. Hartl, M. E. Fermann, and J. Ye, “Phase-stabilized, 1.5 W frequency comb at 2.8–4.8 μm,” Opt. Lett. 34(9), 1330–1332 (2009). [CrossRef]
7. M. Leidinger, S. Fieberg, N. Waasem, F. Kühnemann, K. Buse, and I. Breunig, “Comparative study on three highly sensitive absorption measurement techniques characterizing lithium niobate over its entire transparent spectral range,” Opt. Express 23(17), 21690–21705 (2015). [CrossRef]
8. D. H. Titterton, J. A. C. Terry, D. H. Thorne, I. R. Jones, and D. Legge, “Observation of damage in PPLN,” Proc. SPIE 4268, 5 (2001). [CrossRef]
9. S. Chaitanya Kumar, S. Parsa, and M. Ebrahim-Zadeh, “Fiber-laser-based, green-pumped, picosecond optical parametric oscillator using fan-out grating PPKTP,” Opt. Lett. 41(1), 52–55 (2016). [CrossRef]
10. G. K. Samanta, S. Chaitanya Kumar, A. Aadhi, and M. Ebrahim-Zadeh, “Yb-fiber-laser-pumped, high-repetition-rate picosecond optical parametric oscillator tunable in the ultraviolet,” Opt. Express 22(10), 11476–11487 (2014). [CrossRef]
11. F. Kienle, D. Lin, S. Alam, S. S. Hung, C. B. E. Gawith, H. E. Mahor, D. J. Richardson, and D. P. Shepherd, “Green-pumped, picosecond MgO:PPLN optical parametric oscillator,” J. Opt. Soc. Am. B 29(1), 144–152 (2012). [CrossRef]
12. S. Chaitanya Kumar and M. Ebrahim-Zadeh, “Fiber-laser-based green-pumped picosecond MgO:sPPLT optical parametric oscillator,” Opt. Lett. 38(24), 5349–5352 (2013). [CrossRef]
13. Y. Furukawa, K. Kitamura, A. Alexandrovski, R. K. Route, M. M. Fejer, and G. Foulon, “Green-induced infrared absorption in MgO doped LiNbO3,” Appl. Phys. Lett. 78(14), 1970–1972 (2001). [CrossRef]
14. A. L. Alexandrovski, G. Foulon, L. E. Myers, R. K. Route, and M. M. Fejer, “UV and visible absorption in LiTaO3,” Proc. SPIE 3610, 44 (1999). [CrossRef]
15. G. Hansson, H. Karlsson, S. Wang, and F. Laurell, “Transmission measurements in KTP and isomorphic compounds,” Appl. Opt. 39(27), 5058–5069 (2000). [CrossRef]
16. M. Ebrahimzadeh, G. J. Hall, and A. I. Ferguson, “Singly resonant, all-solid-state, mode-locked LiB3O5 optical parametric oscillator tunable from 652 nm to 2.65 μm,” Opt. Lett. 17(9), 652–654 (1992). [CrossRef]
17. M. J. McCarthy, S. D. Butterworth, and D. C. Hanna, “High-power widely-tunable picosecond pulses from an all-solid-state synchronously-pumped optical parametric oscillator,” Opt. Commun. 102(3-4), 297–303 (1993). [CrossRef]
18. M. Ebrahimzadeh, S. French, W. Sibbett, and A. Miller, “Non-critically phase-matched, Ti:Sapphire-pumped picosecond optical parametric oscillator using LiB3O5,” Appl. Phys. B 60(5), 443–448 (1995). [CrossRef]
19. M. Ebrahimzadeh, S. French, and A. Miller, “Design and performance of a singly resonant picosecond LiB3O5 optical parametric oscillator synchronously pumped by a self-mode-locked Ti:sapphire laser,” J. Opt. Soc. Am. B 12(11), 2180–2191 (1995). [CrossRef]
20. S. French, M. Ebrahimzadeh, and A. Miller, “High-power, high-repetition-rate picosecond optical parametric oscillator for the near- to mid-infrared,” Opt. Lett. 21(2), 131–133 (1996). [CrossRef]
21. S. D. Butterworth, P. G. R. Smith, and D. C. Hanna, “Picosecond Ti:sapphire-pumped optical parametric oscillator based on periodically poled LiNbO3,” Opt. Lett. 22(9), 618–620 (1997). [CrossRef]
22. S. French, A. Miller, and M. Ebrahimzadeh, “Picosecond near- to mid-infrared optical parametric oscillator using KTiOAsO4,” Opt. Quantum Electron. 29(11), 999–1021 (1997). [CrossRef]
23. T. W. Tukker, C. Otto, and J. Greve, “Design, optimization, and characterization of a narrow-bandwidth optical parametric oscillator,” J. Opt. Soc. Am. B 16(1), 90–95 (1999). [CrossRef]
24. D. Bodlaki and E. Borguet, “Picosecond infrared optical parametric amplifier for nonlinear interface spectroscopy,” Rev. Sci. Instrum. 71(11), 4050–4056 (2000). [CrossRef]
25. M. Maus, E. Rousseau, M. Cotlet, G. Schweitzer, J. Hofkens, M. Van der Auweraer, and F. C. De Schryver, “New picosecond laser system for easy tunability over the whole ultraviolet/visible/near infrared wavelength range based on flexible harmonic generation and optical parametric oscillation,” Rev. Sci. Instrum. 72(1), 36–40 (2001). [CrossRef]
26. F. Ganikhanov, S. Carrasco, X. S. Xie, M. Katz, W. Seitz, and D. Kopf, “Broadly tunable dual-wavelength light source for coherent anti-tokes Raman scattering microscopy,” Opt. Lett. 31(9), 1292–1294 (2006). [CrossRef]
27. F. Kienle, P. S. The, D. Lin, S. Alam, J. H. V. Price, D. C. Hanna, D. J. Richardson, and D. P. Shepherd, “High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator,” Opt. Express 20(7), 7008–7014 (2012). [CrossRef]
28. S. Parsa, S. Chaitanya Kumar, B. Nandy, and M. Ebrahim-Zadeh, “Yb-fiber-pumped, high beam-quality, idler-resonant mid-infrared picosecond optical parametric oscillator,” Opt. Express 27(18), 25436–25444 (2019). [CrossRef]
