Open Access
Add to BibSonomy
Abstract
Laser–plasma instabilities (LPIs) hinder the interaction of high-energy laser pulses with targets. Simulations show that broadband spectrally incoherent pulses can mitigate these instabilities. Optimizing laser operation and target interaction requires controlling the properties of these optical pulses. We demonstrate closed-loop control of the spectral density and pulse shape of nanosecond spectrally incoherent pulses after optical parametric amplification in the infrared (∼1053 nm) and sum–frequency generation to the ultraviolet (∼351 nm) using spectral and temporal modulation in the fiber front end. The high versatility of the demonstrated approaches can support the generation of high-energy, spectrally incoherent pulses by future laser facilities for improved LPI mitigation.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
High-energy lasers enable one to explore matter at high temperatures and pressures within the laboratory environment. Compression of a target, either directly by laser beams or indirectly via x rays generated by the interaction of laser beams with matter, holds promise for the development of laser-driven inertial confinement fusion plants [1,2]. Laser–plasma instabilities (LPI’s) are detrimental to efficient target compression because they decrease laser–energy coupling into the target [3]. Simulations show that using broadband, spectrally incoherent pulses can mitigate LPI’s [4–8]. The electric field of these pulses is uncorrelated over time scales longer than their coherence time, which is inversely proportional to their bandwidth and much shorter than their overall duration. The simulation codes have mostly been benchmarked with data obtained using relatively narrowband pulses. There is currently no strict bandwidth requirement established for the design of the next generation of laser drivers, but fractional bandwidths (ratio of bandwidth to carrier frequency) of the order of 1%, e.g., 8.5 THz at 351 nm, are predicted to significantly mitigate the relevant LPI’s. Laser systems with controllable spectral and temporal properties over such bandwidth will support experiments and simulations to better understand LPI mitigation. In the current generation of high-energy, solid-state laser drivers, the optical bandwidth of the coherent laser pulse is increased via temporal phase modulation for beam smoothing [9] and safe operation [10]. Advanced modulation schemes relying on multiple high-frequency modulations have been demonstrated for improved beam uniformity [11]. The bandwidth resulting from phase modulation is well below what is required for LPI mitigation. To support these bandwidths, laser-engineering proposals and efforts have focused on generating broadband, spectrally incoherent pulses on target via laser amplification [12–16]. More recently, optical parametric amplifiers (OPA’s) pumped by frequency-doubled, Nd-doped laser systems, with operation close to spectral degeneracy (1053 nm) for broadband amplification [17], and sum–frequency generation (SFG) of pulses from 1053 nm to 351 nm [18] have been demonstrated.
Precisely controlling the properties of nanosecond laser pulses is required to optimize laser–matter interaction and safely operate high-energy laser facilities below the damage threshold of optical components. Spectral control allows for optimization of the amplification and frequency-conversion stages, for example, by setting the wavelength for peak performance and precompensating for spectral variations [19–21]. It also allows for the control of coherence time and field statistics of an incoherent pulse [8,21–23]. Temporal pulse shaping is commonly performed on high-energy lasers to adapt the time-dependent delivery of laser intensity to the physical state of the target during the interaction [24–26]. On these systems, temporally shaped UV pulses are obtained by nonlinear frequency conversion of the amplified IR pulses in a doubling and tripling crystal [27]. Broadband pulse shaping allows for a wide range of ultrafast optics applications [28], and recently for relatively long pulses of interest for high-energy laser-matter interations [29]. Most demonstrations have been performed with IR pulses, but various techniques have been demonstrated for UV pulses [30–32].
In this work, we demonstrate the versatile and precise control of the spectral and temporal properties of spectrally incoherent nanosecond pulses on a system composed of an OPA operating around 1053 nm (1ω) followed by frequency conversion to 351 nm (3ω) using SFG with a narrowband 526.5-nm (2ω) pulse. Closed-loop algorithms control a Mach–Zehnder modulator (MZM) driven by an arbitrary waveform generator and a programmable spectral filter based on a zero-dispersion line in the fiber front end. Convergence to user-defined spectral and temporal profiles is obtained despite the significant distortions introduced by amplification. The temporal and spectral properties of the 3ω pulse generated by SFG are controlled by the 2ω pulse shape and 1ω spectrum, respectively. The experimental setup is described in Sec.2. Experimental results related to spectral and temporal shaping are presented in Sec.3.
2. Experimental setup
We demonstrate the temporal and spectral shaping of spectrally incoherent pulses in the IR and UV on a system composed of a fiber front end, an OPA stage, an SFG stage, and a frequency-doubled Nd:YLF laser system generating the pump pulse for the OPA and SFG stage (Fig. 1). The fiber front end generates the broadband spectrally incoherent OPA seed and the coherent seed for the pump laser using a single high-bandwidth arbitrary waveform generator (AWG70001A, Tektronix). This architecture allows for the high-resolution generation of optical waveforms with low relative jitter, owing to the large memory and excellent time-base stability of the arbitrary waveform generator [33].
Fig. 1. Experimental setup showing the signal generation at 1ω, pump generation at 2ω, amplification in the LBO OPA stage, and frequency conversion in the KDP SFG stage. The properties of the 1ω, 2ω, and 3ω pulses are measured after the OPA, SHG, and SFG stage, respectively. The insets represent the timing configuration for the 1ω pulse (in red) and the 2ω pulses (in green) within the OPA and SFG stages.
The spectrally incoherent seed pulse is generated using an amplified spontaneous emission (ASE) source (BBS-1μm-22-L, MW Technologies) after temporal shaping by a Mach–Zehnder modulator (MZM), spectral shaping by a programmable filter, and amplification in two Yb-doped fiber amplifiers (FA’s) based on standard single-mode fibers with 6-μm mode-field diameter followed by a custom Yb-doped, large-mode-area (LMA) amplifier with a 10-μm mode-field diameter (Optical Engines). The LMA amplifier allows for amplification of nanosecond pulses at energies up to 1 μJ. The fiber-based generation leads to high spatial coherence of the ASE pulse, which is important for subsequent propagation and nonlinear interactions [17]. The Mach–Zehnder modulator driven by the arbitrary waveform generator (AWG) after amplification leads to a sub-100-ps pulse-shaping resolution. The programmable filter, based on a zero-dispersion line with a liquid-crystal-on-silicon modulator at its Fourier plane (Waveshaper WS-01000A, II–VI), has a spectral resolution of the order of 0.25 nm. This filter can independently control the spectral amplitude and phase, but only amplitude control is relevant for spectrally incoherent pulses. Such a filter offers much greater flexibility than the Lyot-type filter previously used for spectral shaping of incoherent pulses [21]. The seed pulse is launched in free space, collimated, and aligned to the OPA stage.
The pump pulse is generated at 5 Hz by a monochromatic laser at 1053 nm followed by a Mach–Zehnder modulator, a fiber amplifier, a diode-pumped Nd:YLF regenerative amplifier, and a double-pass, diode-pumped Nd:YLF amplifier. Second-harmonic generation (SHG) in a lithium triborate (LBO) crystal leads to ∼90 mJ at 2ω. The pulse-shaping system is configured to generate two time-delayed pump pulses, one for the OPA stage and one for the SFG stage (insets in Fig. 1), with temporal resolution better than 100 ps. Both pulses propagate through the OPA, in which the second pump pulse and the seed are temporally overlapped. After the OPA, the amplified signal and idler pulses are separated from the pump pulses by a dichroic mirror. These pulses are recombined at the SFG crystal with a relative time delay using another dichroic mirror, allowing frequency conversion of the signal and idler with the first pump pulse. This architecture allows one to independently control the interaction in the OPA and SFG stages, as well as the relative timing between pulses. For the experiments reported in this article, the nominal duration of each pump pulse is 1.5 ns and their timing difference is 2.3 ns (defined at their leading edge).
The OPA stage is based on two LBO crystals (total length: 65 mm) set in a collinear geometry, leading to co-propagating signal and idler [17]. The frequency-dependent phase mismatch in the OPA does not depend on the coherence of the signal. The energy efficiency of this stage with broadband spectrally incoherent pulses is similar to that with a monochromatic source at 1030 nm, consistent with previous experimental investigations [17]. It slightly depends on the signal coherence time (inverse of the bandwidth), and operation with narrowband spectrally incoherent pulses (bandwidth smaller than 1 nm at 1030 nm) reduces the efficiency by ∼10% compared to broadband operation (spectral density extending over ∼10 nm). This reduction is expected when the signal coherence time is larger than the relative pump-signal group delay in the OPA (∼3 ps for 65 mm in LBO), as studied via simulations [34]. SFG of the broadband 1ω OPA output pulse with the narrowband 2ω pump pulse is implemented in a 10-mm potassium-dihydrogen-phosphate (KDP) crystal using a noncollinear angularly dispersed geometry [18]. In this work, we focus on shaping the signal after amplification in the OPA stage and frequency conversion in the SFG stage. Owing to energy conservation in the high-gain OPA, the signal and idler have identical temporal pulse shapes and symmetric spectra relative to twice the frequency of the pump, which corresponds to 1053 nm. After optimization, the SFG stage has a symmetric spectral acceptance relative to 1053 nm that leads to identical frequency conversion for the signal and idler [18]. Therefore, only the spectral properties of the signal and temporal properties of the combined signal and idler are presented. The pulses at 1ω, 2ω, and 3ω are sampled after the OPA stage, the SHG stage, and the SFG stage, respectively. Grating spectrometers are used for spectral characterization at 1ω (HR2000+, Ocean Optics) and 3ω (SpectraPro HRS-300, Princeton Instruments, and ML4022 camera, Finger Lakes Instrumentation). The pulse shapes at 1ω, 2ω, and 3ω are measured with 7-GHz silicon photodiodes (UPD-50-UP, ALPHALAS) and a 13-GHz oscilloscope (DSA9104A, Agilent Technologies).
The typical 2ω energy used on this test bed is 90 mJ (split approximately as 60 mJ to pump the OPA stage and 30 mJ to pump the SFG stage) for flat-in-time pulses. Saturation in the OPA stage leads to 15 mJ of energy for the combined signal and idler. Frequency mixing in the SFG stage yields approximately 3 mJ at 3ω, which is consistent with expectations considering the intensities in the KDP crystal [18]. Simulations show that this efficiency is slightly lower than for coherent waves with identical intensities. The temporal walk-off between the 1ω, 2ω, and 3ω waves partially mitigates the impact of the large temporal modulations present on the 1ω pulse and allows for more-uniform depletion of the 2ω pulse in a process similar to what has been observed with OPA’s operating with spectrally incoherent signals [34]. Input waves with higher intensities, e.g., with optimal design of a high-energy laser system, will lead to efficiencies comparable to the current third-harmonic–generation scheme. The mentioned energies are representative of what has been obtained for all the results demonstrated in this article because the system’s parameters were adjusted to take into account the effect of spectral and temporal shaping. In particular, the LMA amplifier gain was adjusted to operate the OPA at saturation for a given pump energy when performing spectral shaping at 1ω, whereas the regenerative-amplifier gain was adjusted to reach saturation in that amplifier when performing temporal shaping at 2ω.
We demonstrate the shaping of spectrally incoherent pulses in the IR (around 1053 nm) and UV (around 351 nm) for four different configurations:
- • spectral shaping of the OPA 1ω output by shaping the seed spectrum
- • temporal shaping of the OPA 1ω output by shaping the OPA 2ω pump pulse
- • spectral shaping of the SFG 3ω output by shaping the OPA output spectrum
- • temporal shaping of the SFG 3ω output by shaping the SFG pump pulse
3. Experimental results
3.1 Spectral shaping of the OPA output signal
The spectrum of the amplified signal measured after the OPA is shaped by controlling the spectrum of the input seed using the programmable spectral filter in the front end. Such shaping can precompensate the wavelength-dependent gain variations in the Yb-doped fiber amplifiers and OPA, although the latter are not expected to be significant, considering that an LBO OPA with that length has a bandwidth larger than 100 nm [17]. Without spectral shaping, the OPA output spectrum peaks at ∼1032 nm and has a full width at half maximum equal to 7 nm.
The wavelength-dependent filter transmission is iteratively modified to decrease the error between the measured spectrum and target spectrum Starget (both peak-normalized to 1) using closed-loop control following
Figure 2 presents spectral-shaping examples for which Starget has been set to a 10-nm flattop profile with a central wavelength ranging from 1032 to 1044 nm [(a)–(d)] and to the same flattop profiles modulated by a parabolic term [(e)–(h)]. This simulates spectral shaping for operation at different central wavelengths with precompensation of spectral gain narrowing in subsequent amplifiers. On all plots, the output spectrum without spectral modulation from the front-end filter and after convergence averaged over 100 successive shots, and the wavelength-dependent filter transmission, in dB, are shown by the thick solid lines. The shaped spectrum for these 100 shots is shown by the thin colored lines to illustrate the impact of spectral incoherence. Excellent spectral shaping is observed, with control of the filter transmission over more than 20 dB to compensate for the low spectral density at longer wavelengths. Target spectra that have no significant spectral components within the bandwidth of the seed require large filter attenuation, up to the 60-dB nominal value achievable by the filter, over most of the input spectrum. This significantly reduces the input energy to the large-mode-area fiber amplifier, resulting in a relative increase of the ASE being generated by this amplifier, as can be observed between 1025 and 1039 nm on Figs. 2(d) and 2(h). Such ASE is amplified similarly to the seed when it temporally overlaps with the pump pulse in the OPA. It can be spectrally filtered, if needed, after the LMA amplifier. Figure 3 demonstrates the capability of the closed-loop spectral shaping system to generate more complex profiles, in particular spectra that include components experiencing optimal gain (e.g., at 1030 nm) and low gain (e.g., at 1045 nm) in the fiber amplifiers. In each case, the target spectrum has been chosen as an arbitrary combination of several flattop and/or Gaussian components extending over ∼20 nm. Stable and excellent convergence is observed in all cases. Because of the large gain variation over the wavelength range of interest, a dynamic range higher than 25 dB is required to reach the target spectral shapes.
Fig. 2. Spectral shaping of the OPA output signal. On the first row [(a)–(d)], Starget is a 10-nm flattop spectrum centered at 1032, 1036, 1040, and 1044 nm, respectively. On the second row [(e)–(h)], Starget is set to a 10-nm flattop spectrum with parabolic modulation centered at the same wavelengths. On all plots, the spectra averaged over 100 acquisitions without and with shaping are plotted using a dashed black line and solid black line, respectively. The spectra acquired over 100 successive shots are plotted with thin colored lines. The transmission of the spectral filter, in dB, is plotted with a thick red line.
Fig. 3. Spectral shaping of the OPA output signal, with Starget set to various combinations of Gaussian and flattop components. On all plots, the spectra averaged over 100 acquisitions without and with shaping are plotted using a black dashed line and black continuous line, respectively. The spectra acquired over 100 successive shots are plotted with thin colored lines. The transmission of the spectral filter, in dB, is plotted with a thick red line.
3.2 Temporal shaping of the OPA output signal
The pulse shape of the coherent signal amplified by an OPA can be controlled using either the pump or signal pulse shape at its input [19,20,35]. In this work, the temporal shape of the amplified spectrally incoherent signal is controlled via the pump pulse shape using the AWG-driven MZM in the fiber front end. Because the SFG stage is not used, the pump laser is set to produce a single pump pulse. Unstable behavior has been observed when a target pulse shape is set for the OPA output signal during closed-loop control. This is attributed to the non-monotonic nature of the relation between pump intensity (set by pulse shaping in the pump front end) and amplified signal intensity because of reconversion. Convergence to a user-defined 2ω pump pulse shape has therefore been chosen, after which the shaped pump pulse allows for temporal shaping of the OPA output pulse. We additionally demonstrate that the temporal and spectral properties of the amplified OPA signal can be controlled independently from each other.
Closed-loop pulse shaping has been implemented between the AWG-driven MZM in the fiber front end and the 2ω pulse shape after SHG. A preliminary calibration based on the generation of short Gaussian pulses at different times within the operation window of the regenerative amplifier maps out the linear relation between the time base of the AWG and oscilloscope. Saturation in the fiber amplifiers and Nd:YLF amplifiers leads to significant square-pulse distortion; i.e., the gain at earlier times is significantly higher than at later times within the pump pulse, while the gain observed at a given time depends on the energy that has been extracted at earlier times. Square-pulse distortion in the laser amplifiers, the nonlinear transfer function of the MZM relative to its drive voltage, and the nonlinear second-harmonic generation make the temporal shaping of the output pulse a complex task. In particular, open-loop control assuming a linear transfer function between input and output is clearly insufficient to generate a user-defined pump pulse. Closed-loop control to generate the pulse shape Ptarget is implemented following
where Wn and Pn are the time-dependent waveform and power at iteration n, respectively. The AWG and MZM are set to implement a monotonic relation between voltage and transmission, while operation at a reference voltage corresponds to the null transmission of the MZM. Several additional steps improve the stability of the process described by Eq. (2). The measured waveform is thresholded to prevent instabilities due to the photodetection noise. It is scaled to favor operation of the MZM at higher transmission to improve the signal-to-noise ratio. The magnitude of the feedback constant η (initially –0.1) is numerically decreased to reduce the impact of measurement noise when the measured pulse is close to the target pulse. Low-pass filtering of the AWG samples is periodically performed to prevent the growth of high-frequency modulations that are attributed to the mismatch between the AWG sampling rate (50 GS/s, i.e., one sample every 20 ps) and the actual pulse shaping and photodetection bandwidth (∼100 ps).Figure 4 shows examples of shaped temporal and spectral properties after the OPA. Without spectral modulation, closed-loop control was used to obtain a flat-in-time, Gaussian, or double-hump pump pulse shape [Figs. 4(a) and 4(d)]. The same process was repeated when the spectral shape was set to a 10-nm-wide flattop profile [Figs. 4(b) and 4(e)] and the combination of a Gaussian and flattop component [Figs. 4(c) and 4(f)]. These results demonstrate the generation of temporally and spectrally shaped incoherent pulses amplified by the OPA.
Fig. 4. Temporal and spectral shaping of the OPA output. Plots (a), (b), and (c) display the measured pulse shape. Plots (d), (e), and (f) display the average measured spectrum. Plots (a) and (d) correspond to a constant spectral-filter transmission, (b) and (e) correspond to the generation of a flattop spectral density, and (c) and (f) correspond to the generation of a spectrum with a Gaussian and a flattop component.
3.3 Spectral shaping of the SFG output signal
The spectrally shaped 1ω pulses from the OPA are converted to spectrally shaped 3ω pulses using SFG with a narrowband 2ω pulse in a noncollinear angularly dispersed geometry. For operation with a signal at 1030 nm and the corresponding idler at 1077 nm, which is the default configuration used for these results, the spectral acceptance of this interaction in a 10-mm KDP crystal is approximately 9 nm around each of these wavelengths [18]. SFG with a monochromatic field translates the input field along the frequency axis, i.e., it leads to identical spectral features for the input 1ω wave and output 3ω waves if the spectral acceptance is large enough. Figure 5 compares the 1ω and 3ω spectra, where the two wavelength ranges have been set to cover the same frequency range. For Fig. 5(a), the spectral-filter transmission is constant, whereas closed-loop control with various target spectra was used for the results shown in Figs. 5(b)–5(e). There is generally good agreement between the measured spectral shapes at 1ω and 3ω, although the latter have broader features because of the lower resolution of the UV spectrometer compared to the IR spectrometer (0.25 THz versus 0.05 THz). The SFG spectral acceptance reduces the conversion efficiency of frequency components away from the central frequency for which the phase matching has been optimized, as seen, in particular, in Figs. 5(b) and 5(e). Tuning the crystal around the reference angle θ0 modifies the phase-matching conditions and adjusts the central frequency for maximal conversion, resulting in 3ω spectra that are biased toward either the longer or shorter wavelengths [Fig. 5(f)].
Fig. 5. Spectral shaping of the SFG output signal corresponding to a shaped OPA output signal. Plots (a)–(e) show the 1ω spectrum (red line) and the 3ω spectrum (blue line), which are plotted over wavelength ranges that correspond to the same frequency span (10 THz). Plot (f) shows the 3ω spectrum corresponding to the 1ω spectrum shown in plot (e) for three different tuning angles of the SFG crystal (blue line: reference angle θ0; cyan line: θ0–0.015°; purple line: θ0 + 0.02°).
3.4 Temporal shaping of the SFG output signal
The SFG process yields an instantaneous intensity at 3ω that depends on the intensities at 1ω and 2ω. The 3ω pulse shape can therefore be controlled via pulse shaping of either the 1ω pulse (obtained via parametric amplification in this demonstration) or 2ω pulse (obtained via frequency conversion of a narrowband 1ω pulse). High conversion efficiencies are expected when the number of photons at 1ω and 2ω in a relevant time interval are approximately equal. For a suitable range of input intensities, the 3ω output intensity is approximately proportional to the input intensity of both waves, allowing for temporal shaping at 3ω by shaping either the 1ω or 2ω pulse. High-contrast pulse shaping can be achieved with both approaches. If shaping the 1ω pulse in an OPA, the dynamic range is limited to the ratio of the highest obtainable signal intensity, essentially a fraction of the pump intensity, to the input signal intensity, i.e., the saturated gain of the amplifier. The amplified 1ω intensity strongly depends on the pump intensity in high-gain stages, therefore facilitating the obtention of high-contrast pulse shapes. A lower-gain amplifier such as the last stage of a high-energy amplification chain might not provide sufficient dynamic range for high-contrast shaping. This can be alleviated by shaping the pump pulse in more than one amplifier. Temporal shaping of the OPA output by shaping the input seed is possible [35], but such control is difficult over a large dynamic range owing to the large small-signal gain and the generation of parametric fluorescence at times when the seed intensity is relatively low.
The angular dispersion added on the 1ω pulse by the 1ω diffraction grating induces pulse-front tilt in the SFG crystal, i.e., a linear variation of the group delay versus transverse position in the direction of the angular dispersion [36]. Interaction with a shaped 2ω pulse yields an angularly dispersed shaped 3ω pulse. The 3ω diffraction grating removes that dispersion but adds a linear spatial dependence of the shaped features relative to the transverse position. Because of this dependence, the 3ω pulse shape averaged over the entire beam is a convolution of the induced pulse shape with a rectangular function having a width αδx, where α is the pulse-front tilt coefficient and δx is the beam width in the direction of angular dispersion. For a nominal angular dispersion Δ = 0.6 mrad/nm inside the SFG crystal with index n, one has α = nλΔ/c, i.e., α = 3.1 ps/mm. This effect is therefore negligible for the small-size beams (∼1 mm) used in this experimental demonstration, but will lead to loss of temporal resolution on laser systems with large beams. If shaping at 3ω is performed by interaction of a flat-in-time 2ω pulse with a shaped 1ω pulse, the shaped features experience both the input angular dispersion at 1ω and the output angular dispersion at 3ω. This approach does not decrease the temporal resolution.
For this demonstration, temporal shaping of the SFG 3ω output signal has been implemented via temporal shaping of the 2ω monochromatic pulse. The target pulse shape for the OPA pump is a high-order super-Gaussian, and the OPA is run at saturation to generate a flat-in-time 1ω pulse. The 2ω pulse generated by the pump laser must therefore be composed of two time-delayed pulses: a high-order super-Gaussian pulse (OPA pump) and a user-defined pulse (SFG pump), the latter defining the 3ω pulse shape after the SFG stage.
Accurate and stable temporal shaping of the 2ω pump pulse has been obtained with the algorithm described in Sec. 3.2. The shaped pulses, composed of the high-order super-Gaussian OPA pump pulse and the user-defined SFG pump pulse, are routed after convergence to the OPA and SFG stage. Figure 6 displays the shaped 2ω pulse and the resulting 3ω pulse for various user-defined profiles. A super-Gaussian OPA pump pulse (second pulse) is consistently obtained, allowing for temporally uniform OPA saturation. This leads to a flat-in-time amplified 1ω signal, and transfer of the SFG pump pulse shape (first pulse) from 2ω to 3ω via SFG.
Fig. 6. Temporal shaping of the 2ω pump pulse (solid green line) and resulting 3ω pulse shape (solid blue line) for target profiles equal to (a) a super-Gaussian pulse, (b) a positive ramp, (c) a negative ramp, (d) a modulated super-Gaussian pulse, (e) a pair of short pulses with identical amplitudes, and (f) a pair of short pulses with unequal amplitudes. The 2ω pulse is composed of the SFG pump pulse (first pulse) and the OPA pump pulse (second pulse).
4. Conclusions
We have demonstrated the control of the spectral and temporal properties of incoherent pulses in the infrared and the ultraviolet. Closed-loop control algorithms have been implemented based on modulation in the fiber front end and measurements after the OPA and SHG stages, respectively. In particular, SFG of the OPA output with a monochromatic pulse transfers the spectral properties of the infrared pulse and temporal properties of the pump pulse to the ultraviolet pulse. This allows one to accurately control these properties using well-developed technologies operating in the fiber front end.
The demonstrated shaping approaches are applicable to larger high-energy facilities. The spectral acceptance of OPA’s with Type-I phase matching allows the generation of broadband spectrally incoherent pulses close to spectral degeneracy. This can be supported at high energy with KDP and DKDP crystals grown at large aperture [37]. These crystals can also support the broadband SFG of spectrally incoherent pulses with a monochromatic pump pulse, with the additional advantage that the OPA and SFG stages can be pumped by a pulse originating from a single frequency-doubled, Nd:doped laser system. These features make the demonstrated architecture and techniques attractive to support the generation of high-energy, spectrally incoherent pulses by laser facilities.
Funding
National Nuclear Security Administration (DE-NA0003856); Office of Science (DE-SC0021032); University of Rochester; New York State Energy Research and Development Authority.
Acknowledgment
The authors thank Alexander Bolognesi, Ted Borger, and Elizabeth Hill for their contributions to the experimental test bed. Portions of this work were presented at the Advanced Solid-State Laser Conference 2021, paper ATh3A.5. This report was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.
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. R. S. Craxton, K. S. Anderson, T. R. Boehly, V. N. Goncharov, D. R. Harding, J. P. Knauer, R. L. McCrory, P. W. McKenty, D. D. Meyerhofer, J. F. Myatt, A. J. Schmitt, J. D. Sethian, R. W. Short, S. Skupsky, W. Theobald, W. L. Kruer, K. Tanaka, R. Betti, T. J. B. Collins, J. A. Delettrez, S. X. Hu, J. A. Marozas, A. V. Maximov, D. T. Michel, P. B. Radha, S. P. Regan, T. C. Sangster, W. Seka, A. A. Solodov, J. M. Soures, C. Stoeckl, and J. D. Zuegel, “Direct-drive inertial confinement fusion: A review,” Phys. Plasmas 22(11), 110501 (2015). [CrossRef]
2. J. D. Lindl, “Development of the indirect-drive approach to inertial confinement fusion and the target physics basis for ignition and gain,” Phys. Plasmas 2(11), 3933–4024 (1995). [CrossRef]
3. D. S. Montgomery, “Two decades of progress in understanding and control of laser plasma instabilities in indirect drive inertial fusion,” Phys. Plasmas 23(5), 055601 (2016). [CrossRef]
4. J. J. Thomson and J. I. Karush, “Effects of finite-bandwidth driver on the parametric instability,” Phys. Fluids 17(8), 1608–1613 (1974). [CrossRef]
5. S. P. Obenschain, N. C. Luhmann, and P. T. Greiling, “Effects of finite-bandwidth driver pumps on the parametric-decay instability,” Phys. Rev. Lett. 36(22), 1309–1312 (1976). [CrossRef]
6. D. Eimerl and A. J. Schmitt, “StarDriver: An estimate of the bandwidth required to suppress the 2(pe instability,” Plasma Phys. Control. Fusion 58(11), 115006 (2016). [CrossRef]
7. R. Follett, J. G. Shaw, D. H. Edgell, C. Dorrer, J. Bromage, E. M. Campbell, E. M. Hill, T. J. Kessler, J. P. Palastro, J. F. Myatt, J. W. Bates, and J. L. Weaver, “Suppressing parametric instabilities with laser-frequency detuning and bandwidth,” APS Division of Plasma Physics Meeting 2018, NI2.005 (2018).
8. R. K. Follett, J. G. Shaw, J. F. Myatt, C. Dorrer, D. H. Froula, and J. P. Palastro, “Thresholds of absolute instabilities driven by a broadband laser,” Phys. Plasmas 26(6), 062111 (2019). [CrossRef]
9. S. Skupsky, R. W. Short, T. Kessler, R. S. Craxton, S. Letzring, and J. W. Soures, “Improved laser-beam uniformity using the angular dispersion of frequency-modulated light,” J. Appl. Phys. 66(8), 3456–3462 (1989). [CrossRef]
10. J. R. Murray, J. R. Smith, R. B. Ehrlich, D. T. Kyrazis, C. E. Thompson, T. L. Weiland, and R. B. Wilcox, “Experimental observation and suppression of transverse stimulated Brillouin scattering in large optical components,” J. Opt. Soc. Am. B 6(12), 2402–2411 (1989). [CrossRef]
11. C. Dorrer, R. Roides, R. Cuffney, A. V. Okishev, W. A. Bittle, G. Balonek, A. Consentino, E. Hill, and J. D. Zuegel, “Fiber front end with multiple phase modulations and high-bandwidth pulse shaping for high-energy laser-beam smoothing,” IEEE J. Sel. Top. Quantum Electron. 19(6), 219–230 (2013). [CrossRef]
12. H. Nakano, T. Kanabe, K. Yagi, K. Tsubakimoto, M. Nakatsuka, and S. Nakai, “Amplification and propagation of partially coherent amplified spontaneous emission from Nd:glass,” Opt. Commun. 78(2), 123–127 (1990). [CrossRef]
13. B. Afeyan and S. Hüller, “Optimal control of laser plasma instabilities using spike trains of uneven duration and delay (STUD pulses) for ICF and IFE,” EPJ Web Conf. 59, 05009 (2013). [CrossRef]
14. D. Eimerl, E. M. Campbell, W. F. Krupke, J. Zweiback, W. L. Kruer, J. Marozas, J. Zuegel, J. Myatt, J. Kelly, D. Froula, and R. L. McCrory, “StarDriver: A flexible laser driver for inertial confinement fusion and high energy density physics,” J. Fusion Energ. 33(5), 476–488 (2014). [CrossRef]
15. S. Obenschain, R. Lehmberg, D. Kehne, F. Hegeler, M. Wolford, J. Sethian, J. Weaver, and M. Karasik, “High-energy krypton fluoride lasers for inertial fusion,” Appl. Opt. 54(31), F103–F122 (2015). [CrossRef]
16. Y. Gao, Y. Cui, L. Ji, D. Rao, X. Zhao, F. Li, D. Liu, W. Feng, L. Xia, J. Liu, H. Shi, P. Du, J. Liu, X. Li, T. Wang, T. Zhang, C. Shan, Y. Hua, W. Ma, X. Sun, X. Chen, X. Huang, J. Zhu, W. Pei, Z. Sui, and S. Fu, “Development of low-coherence high-power laser drivers for inertial confinement fusion,” Matter Radiat, Extremes 5(6), 065201 (2020). [CrossRef]
17. C. Dorrer, E. M. Hill, and J. D. Zuegel, “High-energy parametric amplification of spectrally incoherent broadband pulses,” Opt. Express 28(1), 451–471 (2020). [CrossRef]
18. C. Dorrer, M. Spilatro, S. Herman, T. Borger, and E. M. Hill, “Broadband sum-frequency generation of spectrally incoherent pulses,” Opt. Express 29(11), 16135–16,152 (2021). [CrossRef]
19. H. W. Lee, Y. G. Kim, J. Y. Yoo, J. W. Yoon, J. M. Yang, H. Lim, C. H. Nam, J. H. Sung, and S. K. Lee, “Spectral shaping of an OPCPA preamplifier for a sub-20-fs multi-PW laser,” Opt. Express 26(19), 24775–24,783 (2018). [CrossRef]
20. F. Batysta, R. Antipenkov, T. Borger, A. Kissinger, J. T. Green, R. Kananavičius, G. Chériaux, D. Hidinger, J. Kolenda, E. Gaul, B. Rus, and T. Ditmire, “Spectral pulse shaping of a 5 Hz, multi-joule, broadband optical parametric chirped pulse amplification frontend for a 10 PW Laser System,” Opt. Lett. 43(16), 3866–3869 (2018). [CrossRef]
21. D. Rao, Y. Gao, Y. Cui, L. Ji, X. Zhao, J. Liu, D. Liu, F. Li, C. Shan, H. Shi, J. Liu, W. Feng, X. Li, W. Ma, and Z. Sui, “J nanosecond low-coherent laser source with precise temporal shaping and spectral control,” Opt. Laser Technol. 122, 105850 (2020). [CrossRef]
22. C. Dorrer, “Statistical analysis of incoherent pulse shaping,” Opt. Express 17(5), 3341–3352 (2009). [CrossRef]
23. V. Binjrajka, C.-C. Chang, A. W. R. Emanuel, D. E. Leaird, and A. M. Weiner, “Pulse shaping of incoherent light by use of a liquid-crystal modulator array,” Opt. Lett. 21(21), 1756– 1758 (1996). [CrossRef]
24. C. A. Haynam, P. J. Wegner, J. M. Auerbach, M. W. Bowers, S. N. Dixit, G. V. Erbert, G. M. Heestand, M. A. Henesian, M. R. Hermann, K. S. Jancaitis, K. R. Manes, C. D. Marshall, N. C. Mehta, J. Menapace, E. Moses, J. R. Murray, M. C. Nostrand, C. D. Orth, R. Patterson, R. A. Sacks, M. J. Shaw, M. Spaeth, S. B. Sutton, W. H. Williams, C. C. Widmayer, R. K. White, S. T. Yang, and B. M. Van Wonterghem, “National Ignition Facility laser performance status,” Appl. Opt. 46(16), 3276–3303 (2007). [CrossRef]
25. V. N. Goncharov, T. C. Sangster, T. R. Boehly, S. X. Hu, I. V. Igumenshchev, F. J. Marshall, R. L. McCrory, D. D. Meyerhofer, P. B. Radha, W. Seka, S. Skupsky, C. Stoeckl, D. T. Casey, J. A. Frenje, and R. D. Petrasso, “Demonstration of the highest deuterium-tritium areal density using multiple-picket cryogenic designs on OMEGA,” Phys. Rev. Lett. 104(16), 165001 (2010). [CrossRef]
26. C. A. Thomas, E. M. Campbell, K. L. Baker, D. T. Casey, M. Hohenberger, A. L. Kritcher, B. K. Spears, S. F. Khan, R. Nora, D. T. Woods, J. L. Milovich, R. L. Berger, D. Strozzi, D. D. Ho, D. Clark, B. Bachmann, L. R. Benedetti, R. Bionta, P. M. Celliers, D. N. Fittinghoff, G. Grim, R. Hatarik, N. Izumi, G. Kyrala, T. Ma, M. Millot, S. R. Nagel, P. K. Patel, C. Yeamans, A. Nikroo, M. Tabak, M. Gatu Johnson, P. L. Volegov, and S. M. Finnegan, “Experiments to explore the influence of pulse shaping at the National Ignition Facility,” Phys. Plasmas 27(11), 112708 (2020). [CrossRef]
27. R. S. Craxton, “High efficiency frequency tripling schemes for high power Nd:glass lasers,” IEEE J. Quantum Electron. QE 17(9), 1771–1782 (1981). [CrossRef]
28. A. M. Weiner, “Ultrafast optical pulse shaping: A tutorial review,” Opt. Commun. 284(15), 3669–3692 (2011). [CrossRef]
29. D. E. Mittelberger, R. Muir, D. Perlmutter, and J. Heebner, “Programmable, direct space-to-time picosecond resolution pulse shaper with nanosecond record,” Opt. Lett. 46(8), 1832–1835 (2021). [CrossRef]
30. L. L. Lazzarino, M. M. Kazemi, C. Haunhorst, C. Becker, S. Hartwell, M. A. Jakob, A. Przystawik, S. Usenko, D. Kip, I. Hartl, and T. Laarmann, “Shaping femtosecond laser pulses at short wavelength with grazing-incidence optics,” Opt. Express 27(9), 13479–13,491 (2019). [CrossRef]
31. E. Hertz, F. Billard, G. Karras, P. Béjot, B. Lavorel, and O. Faucher, “Shaping of ultraviolet femtosecond laser pulses by Fourier domain harmonic generation,” Opt. Express 24(24), 27702–27714 (2016). [CrossRef]
32. D. S. N. Parker, A. D. G. Nunn, R. S Minns, and H. H. Fielding, “Frequency doubling and Fourier domain shaping the output of a femtosecond optical parametric amplifier: Easy access to tuneable femtosecond pulse shapes in the deep ultraviolet,” Appl. Phys. B 94(2), 181–186 (2009). [CrossRef]
33. C. Dorrer, W. A. Bittle, R. Cuffney, M. Spilatro, E. M. Hill, T. Z. Kosc, J. H. Kelly, and J. D. Zuegel, “Characterization and optimization of an eight-channel time-multiplexed pulse-shaping system,” J. Lightwave Technol. 35(2), 173–185 (2017). [CrossRef]
34. C. Dorrer, “Optical parametric amplification of spectrally incoherent pulses,” J. Opt. Soc. Am. B 38(3), 792–804 (2021). [CrossRef]
35. C. Dorrer, A. Consentino, R. Cuffney, I. A. Begishev, E. M. Hill, and J. Bromage, “Spectrally tunable, temporally shaped parametric front end to seed high-energy Nd:glass laser systems,” Opt. Express 25(22), 26802–26,814 (2017). [CrossRef]
36. Z. Bor, B. Rácz, G. Szabó, M. Hilbert, and H. A. Hazmin, “Femtosecond pulse front tilt caused by angular dispersion,” Opt. Eng. 32(10), 2501–2504 (1993). [CrossRef]
37. J. J. De Yoreo, A. K. Burnham, and P. K. Whitman, “Developing KH2PO4 and KD2PO4 crystals for the world’s most power laser,” Int. Mater. Rev. 47(3), 113–152 (2002). [CrossRef]
