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Abstract
We report a study of a compact, scalable up to TW peak power OPCPA with ∼1.2 ps pump pulses delivered from a Yb:YAG laser. Passive synchronization was ensured by using a small portion of the energy to generate a stable supercontinuum in the YAG, and the rest was directed to pump the three OPCPA stages. The temporal shape of the pump pulse was controlled by the degree of depletion of fundamental radiation in a two-cascade second harmonic converter. Under optimal conditions, the energy of amplified pulses reached ∼2.1 mJ with the support of a spectral bandwidth sufficient for a transform-limited pulse width of 8.6 fs.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Cost-efficient and compact next-generation lasers with TW levels of peak power are in demand for emerging applications in biology, medicine, microelectronics, molecular and materials science [1–3]. Since the first demonstration in 1992 [4] Optical Parametric Chirped Pulse Amplification (OPCPA) has become an attractive alternative [5,6] to Ti:Sapphire amplifiers and has opened a new horizons for the generation of few-cycle, high intensity pulses. Compared to Ti:Sapphire laser systems, OPCPA provides greater flexibility in achievable pulsewidth and center wavelength, due to its exceptional bandwidth [7]. Therefore, amplification to very high energies is achievable without significantly limiting the bandwidth due to gain narrowing. OPCPA systems based on non-collinear parametric amplification (NOPA) provide amplification bandwidths sufficient for generating pulses of less than 10 fs with a TW level of peak power [8–11]. Recent improvements in the quality and availability of high average power diode-pumped solid-state lasers [12–14], which provide multi-mJ pulses for pumping OPCPA, have made it possible to increase the average power of a few-cycle TW-level OPCPA system to tens of watts [15].
To achieve maximum peak and average OPCPA power, the pumping pulsewidth can also be important. Shorter pulses (from a few ps to sub-ps) make it possible to increase the peak OPCPA pump power due to the inherent scaling of the damage threshold with a reduction in pulsewidth [16]. The high pump intensity makes it possible to achieve the necessary gain in shorter crystals and narrower pump beams, which leads to a greater gain bandwidth [17], an increase in the temporal contrast and simplifies stretchers and compressors [18]. Recent developments have also shown the possibility of using the same sub-ps pump laser to generate a white light supercontinuum (WLC) using it as a seed for OPCPA [12,19], which greatly simplifies the laser configuration by eliminating the need for synchronization between the seed and pump lasers [20,21]. Since the gain in OPCPA is sensitive to the pump intensity, therefore, to the temporal and spatial shape of the pump pulse [22].
A pump with a Gaussian temporal profile is most often used and a substantial part of the pump energy is discarded, which reduces the overall efficiency of parametric amplification. If the seed and pump pulses are comparable in pulsewidth, the gain along the chirped seed pulse is non-uniform, which usually leads to a narrowing of amplified pulse spectrum. Pump pulses with a rectangular temporal profile and a pulsewidth comparable to the seed pulsewidth provide uniform gain for all spectral components of the seed, which avoids the spectral gain narrowing, increases the pump-to-signal conversion efficiency [23] and improves the contrast of amplified pulses relative to the parametric superfluorescence background [24]. The advantage of using temporally shaped pump pulses in OPCPA has been demonstrated for pulsewidth of ∼1 ns [23] and ∼100 ps using pulse stacking [17] and cascaded second harmonic generation (SHG) [10,15,25]. Controlling the shape of significantly shorter pump pulses of the order of ∼1 ps is insufficiently studied, since the use of a spatial light modulator or acousto-optic programmable dispersive filter (AOPDF) in this case is difficult due to the narrow pulse spectrum and insufficient temporal resolution of optoelectronic circuits. The advantages of spatiotemporal flattening of 2 ps pump pulses to mitigate back-conversion in cascaded SHG and to prevent early saturation in the OPCPA stages while maintaining broadband gain are mentioned in a recent publication [26]. However, most studies use a fixed SHG depletion of 50% [10,15] or 37% [26], which leads to the only possible flat-top pulse envelope. To develop advanced lasers with high peak power, a more detailed investigation of the OPCPA bandwidth control by temporal shaping of picosecond pump pulse is necessary.
In this paper, we report on an OPCPA study with a control of the temporal shape of 1.15 ps pump pulses by the degree of depletion of the fundamental radiation in two-cascade SHG. In particular, we present the experimental results of the influence of Gaussian, flat-top, and M-shaped pump pulses on the spectral bandwidth of amplified pulses with a conversion efficiency of 40%, 50%, and 62% in the first SHG cascade, respectively. Based on this investigation, a demonstration laser system with high output peak power was built. It consists of easily reproducible modules: fiber seed laser front-end, a two-stage double-pass chirped pulse amplifier (CPA) based on Yb:YAG rods with a grating compressor [27], WLC generation in YAG, two-cascaded SHG, three OPCPA stages and pulse compressor. The use of the same Yb:YAG laser with a pulsewidth of 1.15 ps for OPCPA pumping and WLC provides inherent synchronization and, thus, greatly simplifies the scheme. Particular attention was paid to increasing the energy conversion efficiency, as well as maintaining a wide spectral bandwidth due to the temporal shaping of 1.15 ps pump pulses by cascaded SHG. Under optimal conditions, an amplified pulse energy of ∼2.1 mJ was achieved with the support of a spectral bandwidth sufficient for a transform-limited pulsewidth of 8.6 fs. Despite the prisms used did not allow demonstrating the pulsewidth much less than 20 fs after compression, in our opinion, the combination of chirped mirrors and prisms or AOPDF would allow obtaining much shorter pulses. Based on the developed layout, depending on the number and power of laser diodes used in CPA [27], the peak output power can be increased to ∼1 TW. In addition, other commercially available lasers that provide similar pump intensities and pulsewidth can also be used to pump the described OPCPA.
2. Experimental setup
The layouts of the pumping source and OPCPA (Fig. 1) were assembled on an optical table measuring 1 × 3 m2. Temporally stretched pulses at a central wavelength of 1030 nm with an energy of 6.5 µJ were selected using a Pockels cell from all-in-fiber seed laser operating at 21 kHz. Square aperture Yb:YAG rods 20 mm long and a doping level 2 at. % in two CPA stages were pumped by high-brightness laser diodes at 940 nm in pulsed operation. Compressed pulses with energies up to 20 mJ, energy stability StDev ± 0.75%, pulsewidth of 1.15 ps and excellent beam quality M2 ∼1.05 were used to generate WLC and pump three OPCPA stages (OPA 1 – OPA 3).
Fig. 1. Experimental laser setup: WLC – white light supercontinuum generator, SHG – second harmonic converter, OPA 1, OPA 2 and OPA 3 – OPCPA stages, CMP – prism compressor, AC – autocorrelator, λ/2 – half-wave retardation plates, TFP – thin film polarizers, NDF – neutral density filter, AL – achromatic lens, F – short-pass interference filter, S – harmonics separator, BS – beam splitter, N-BK7 – glass plate.
A small portion (∼100 µJ) of the pumping source energy was used to generate WLC in an undoped YAG rod 15 mm long. The thin film polarizer (TFP), together with the half-wave retardation plate (λ/2) form an attenuator for the energy of the incident pulses, while the iris aperture apodizes the beam with an initial diameter of 6.4 mm. The crystal length and focusing lens were chosen to produce a stable and broadband WLC. The generated WLC is selected using a short-pass filter (Thorlabs FESH1000) and collimated with an achromatic lens AL (Thorlabs AC127-030-B-ML). The energy stability of WLC pulses was measured using a Si photodetector (Thorlabs DET10A) and an oscilloscope (Tektronix DPO3034). Spectral measurements were carried out using a spectrometer (Avantes AvaSpec-3648-USB2) with an integration time of 100 ms.
OPCPA pump pulses were obtained in two-cascade SHG using LBO crystal in the first cascade (2 mm long, type I, θ = 90°, ϕ = 13.1°) and BBO crystal in the second (2 mm long, type I, θ = 23.4°, ϕ = 90°). The use of BBO crystal in the second SHG cascade is due to its availability in our laboratory, although the use of LBO is preferable when increasing the average pump power. The temporal shapes of pulses converted to the second harmonic were measured by cross-correlation technique with temporal resolution of ∼150 fs.
WLC pulses were amplified in three consecutive OPCPA stages: OPA 1, OPA 2 and OPA 3 based on 2 mm long BBO crystals (Type I, non-collinearity angle α ≈ 2.5° and phase matching angle θ ≈ 24.6°) placed in the ovens set at 40°C. The stages OPA 1 and OPA 2 were phase-matched in the Poynting vector walk-off compensation configuration providing better OPCPA efficiency for narrow beams, while the last stage (OPA 3) used tangential phase matching geometry, which is less prone to parasitic second harmonic generation of the signal and idler. In order to minimize parametric superfluorescence, the first OPCPA stage operated at a limited pump intensity of ∼45 GW/cm2, which is approximately ∼1.5 times lower than the saturation level. The pump intensity for the second stage has already been increased to ∼65 GW/cm2, reaching the saturation level. To demonstrate the compression capabilities of amplified pulses, fused silica quartz prisms with an apex angle of 68.7°, spaced 1.55 m apart and an autocorrelator (APE PulseCheck-50) were used.
The intensity profiles of the pump beams were measured using a CMOS beam profiler (DataRay WinCamD-LCM), and M2 measurements of amplified pulses after compression were carried out using beam propagation analyser (Ophir BeamSquared-SP920).
3. Results and discussion
A stable WLC was observed using an aperture of 5.8 mm diameter and a focusing lens f = 200 mm, providing a beam waist diameter of 70 µm at a depth of 2 mm from the input surface of the YAG crystal. The ratio of the energy stability of WLC and the pump pulse as a function of the pump energy is shown in Fig. 2(a) with three different behaviours (indicated 1,2 and 3). Initially (1), at a pump energy of ∼10 µJ, a single WLC filament is more stable in energy than pumping, and the collimated beam has a clear Gaussian spatial distribution. For pump energies exceeding ∼12 µJ, the pump pulse refocuses to form a second (at 15 µJ) and third (at 20 µJ) longitudinal filament, leading to distortions in the beam profile and higher energy fluctuations. Under optimal excitation conditions in the single filament regime, no degradation of the beam quality or a change in the spectral envelope was observed during testing for 1 hour, corresponding to more than 360 thousand pulses (Fig. 2(b)). Thus, the wide spectral bandwidth of the WLC when pumped by picosecond pulses, good energy and spectral stability, and excellent beam quality make it the preferred choice for passively synchronized OPCPA.
Fig. 2. (a) The ratio of the energy stability of the WLC and the pump pulse as a function of pump pulse energy. Insets: WLC near-field beam intensity profiles. (b) Averaged WLC spectra (black) for 1 hour of operation with deviations (grey area).
The first SHG cascade provides frequency converted pulses with a Gaussian temporal profile of ∼1.2 ps FWHM with an efficiency of 62% (Fig. 3(a)). Significant depletion of the fundamental radiation leads to the formation of an intensity dip in the temporal profile of the pulse [25]. This depleted fundamental pulse is reused in the second SHG cascade, providing an M-shaped temporal profile (Fig. 3(b) – solid line) with a pulsewidth of ∼2 ps at a conversion efficiency of 70% (Fig. 3(a)). Thus, the temporal shape of the second harmonic pulse strongly depends on the conversion efficiency in the first SHG cascade (Fig. 3(b)). Less depletion of the fundamental pulse leads to second harmonics pulses with a flat-top or close to Gaussian temporal profile (Fig. 3(b), dashed and dotted lines), but with lower output energy due to a decrease in the conversion efficiency in the first SHG cascade. Meanwhile, the integral spatial beam profile at the output of the second SHG cascade remains close to Gaussian, as shown in (Fig. 3(c)).
Fig. 3. (a) SHG conversion efficiency in the first (circles) and second (triangles) SHG cascades. (b) Temporal and (c) spatial profiles of the second harmonic pulse after the second SHG cascade with the conversion efficiency in the 1st cascade of 62% (solid), 50% (dashed) and 40% (dotted).
In order to efficiently use pump radiation and minimize the spectral gain narrowing, M-shaped pulses were directed to pump the first and second OPCPA stages with high gain, and pulses with a Gaussian temporal profile were delivered for the last stage. An overall conversion efficiency of 85% was achieved with two output beams: with an energy of 12 mJ (Gaussian) and 5 mJ (M-shaped) for pumping OCPCA. True, in order to reduce Kerr self-focusing during propagation in air, the energy of the pumping source was limited to 10 mJ and 4.2 mJ, respectively. For the same purpose, the SHG cascades were placed as close as possible to the OPCPA stages, and the beam formation telescopes were slightly detuned. The use of vacuum cells in the path of the pump beam would make it possible to use without limitation the energy of the pumping source.
The output energy of the second SHG cascade was divided into two beams with energies of 0.6 mJ and 3.6 mJ for pumping the OPA 1 and OPA 2 stages, respectively. In the first OPCPA stage, WLC pulses are amplified up to 5.4 µJ with a pump-to-signal efficiency of 0.9%. The output pulse energy of 300 µJ was achieved in the second OPCPA stage with an efficiency of 8.2%, while the pulse spectrum (Fig. 4(a), solid line) corresponds to transform limited pulsewidth of 8.1 fs. The wavelength range of the amplified pulses from 670 nm to 1000 nm was limited by the gain bandwidth of the BBO crystal under the described phase matching conditions.
Fig. 4. (a) Spectrum of WLC (grey area) and amplified pulses after two OPCPA stages pumped by M-shaped (solid), flat-top (dashed) and Gaussian (dotted) pulses. Spectra are given without reference to relative amplitudes. (b) Spectrum of amplified pulses after three OPCPA stages. Inset – autocorrelation trace after compression (solid) with a Gaussian fit (dotted line).
In order to compare the spectral narrowing of OPCPA with the different temporal shape of the pump pulses, the output energy from the Yb:YAG pumping source was reduced to ensure the conversion efficiency of 40% and 50% at the first SHG cascade. The spectra obtained by pumping the first two OPCPA stages with Gaussian (dotted line), flat-top (dashed line) and M-shaped pulses at the same intensity of the incident pump are shown in Fig. 4(a). It can be seen that in the case of pumping by Gaussian and flat-top pulses, the gain bandwidth decreases significantly due to the weakening of the gain on the wings of the pulse, which leads to 11 fs and 9.7 fs calculated transform limited pulsewidth, respectively. As expected, the best gain bandwidth is achieved with M-shaped pump pulses due to the higher gain for the spectral components at the leading and trailing edges of the seed.
The ratio between the seed and pump pulsewidth was estimated by stretching the signal as it passed through N-BK7 glass plates to NOPA cascades. Direct measurement of the pulsewidth of a WLC seed was difficult due to its low pulse energy. Thus, the optimum glass plate thickness of 20 mm was experimentally found by optimizing the efficiency-bandwidth product ηΔν [28] after the second OPCPA stage, pumped by Gaussian pulses. Further stretching of the signal pulse was limited by the use of a pump of 1.2 ps pulsewidth in the third OPCPA stage. This, in turn, leads to a decrease in the pump-to-signal conversion efficiency when using a flat-top and especially M-shaped pump pulses. However, to improve the conversion efficiency in the second OPCPA stage, it would be desirable to further stretch the signal pulses so that they correspond to M-shaped pump pulses with a pulsewidth of ∼2 ps. A summary of the performance of the second OPCPA stage pumped with different pulse shapes is presented in Table 1.
Table 1. Comparison of the performance of the second OPCPA stage pumped with different pulse shapes: τp is the pulsewidth of the pump pulse (FWHM), Ep and Es are the energies of the pump pulse and the amplified signal after the OPA 2 stage, respectively, η is the pump-to-signal conversion efficiency and FTL is transform-limited pulsewidth, estimated from the amplified signal spectrum, ETp is the total pump energy available at 515 nm for all three OPCPA stages.
The third stage of OPCPA (OPA 3) used 10 mJ Gaussian pump pulses from the first SHG cascade. Due to the high signal energy, the pump intensity was reduced compared to the previous stage to ∼50 GW/cm2, and a strong saturation level was achieved. The pump-to-signal conversion efficiency increased to ∼20%, the pulse energy reached ∼2.1 mJ, and its spectrum (Fig. 4(b)) corresponded to Fourier-limited pulsewidth of ∼8.6 fs.
Thus, the two-cascade SHG configuration is suitable for pumping a multi-stage OPCPA, since the control of the temporal shape of the pump pulses in the first high gain stages allows maintaining a wide spectral bandwidth, and the Gaussian pump pulses of the third low gain OPCPA stage provide efficient energy extraction. The achieved energy of amplified pulses after three OPCPA stages using M-shaped pump pulses obviously exceeds the energy obtained using the Gaussian or flat-top pulses due to large losses of fundamental radiation in the SHG converter for the last two cases, since the total available pump energy decreases from 14.2 mJ to 7.6 mJ and 4.1 mJ, respectively.
The experimentally achieved pulsewidth τp = 20 fs after compression assuming a Gaussian temporal profile (Fig. 4(b), inset) is limited by a higher order residual positive dispersion, which mainly corresponds to the dispersion of the YAG crystal for WLC. Ultimately, this can be compensated by AOPDF or specially designed chirped mirrors.
The beam quality of the amplified pulses after compression was measured at a central wavelength of 790 nm using a transmission filter with a bandwidth of 15 nm (FWHM). The average values of M2 for a flat-top and M-shaped pump pulses were close within the measurement error and amounted to 1.25 and 1.21, respectively (Fig. 5). When using Gaussian pump pulses, the assembled measuring setup for determining M2 of compressed pulses did not allow reliable determination of the beam quality due to a significant decrease in the output energy. The beam profiles (Fig. 5, insets) were close to Gaussian and were similar for both cases.
Fig. 5. M2 measurements of amplified pulses after compression using (a) flat-top and (b) M- shaped pump pulses. Insets: beam intensity profiles in three positions from the waist location.
4. Summary
We reported on a study of a passively synchronized TW-class OPCPA pumped and seeded with a picosecond Yb:YAG CPA pumping source. The temporal shape of ∼1.2 ps pump pulses was controlled by the degree of depletion of the fundamental radiation in a two-cascaded second harmonic converter. The use of M-shaped pump pulses made it possible to maintain a wide spectral bandwidth of amplified pulses in OPCPA stages with a high gain, while Gaussian pump pulses provided efficient energy extraction at the last stage. In addition, two-cascaded harmonic configuration significantly increases the overall conversion efficiency of the pump radiation at the fundamental wavelength into pulses amplified by OPCPA. Based on this study, a demonstration laser system was built with an output energy of 2.1 mJ at a repetition rate of 100 Hz with support of a spectral bandwidth corresponding to a transform-limited pulsewidth of 8.6 fs.
Funding
Research Council of Lithuania (LAT-10/2016).
Acknowledgment
We thank Augustinas Petrulenas and Vytenis Girdauskas for their great contribution to the experiments, as well as Dr. Andrejus Michailovas and Dr. Rokas Danilevičius for fruitful discussions. Portions of this work were presented at the “Advanced Solid State Lasers 2019” conference in 2019, paper AM2A.7.
Disclosures
The authors declare no conflicts of interest.
References
1. E. Gagnon, P. Ranitovic, X. M. Tong, C. L. Cocke, M. M. Murnane, H. C. Kapteyn, and A. S. Sandhu, “Soft X-ray-driven femtosecond molecular dynamics,” Science 317(5843), 1374–1378 (2007). [CrossRef]
2. H. J. Wörner, J. B. Bertrand, D. V. Kartashov, P. B. Corkum, and D. M. Villeneuve, “Following a chemical reaction using high-harmonic interferometry,” Nature 466(7306), 604–607 (2010). [CrossRef]
3. K. Sugioka and Y. Cheng, “Ultrafast lasers – reliable tools for advanced materials processing,” Light: Sci. Appl. 3(4), e149 (2014). [CrossRef]
4. A. Dubietis, G. Jonušauskas, and A. Piskarskas, “Powerful femtosecond pulse generation by chirped and stretched pulse parametric amplification in BBO crystal,” Opt. Commun. 88(4-6), 437–440 (1992). [CrossRef]
5. A. Jullien, A. Ricci, F. Böhle, J. Rousseau, S. Grabielle, N. Forget, H. Jacqmin, B. Mercier, and R. Lopez-Martens, “Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system,” Opt. Lett. 39(13), 3774–3777 (2014). [CrossRef]
6. B. Langdon, J. Garlick, X. Ren, D. Wilson, A. Summers, S. Zigo, M. Kling, S. Lei, C. Elles, E. Wells, E. Poliakoff, K. Carnes, V. Kumarappan, I. Ben-Itzhak, and C. Trallero-Herrero, “Carrier-envelope-phase stabilized terawatt class laser at 1 kHz with a wavelength tunable option,” Opt. Express 23(4), 4563–4572 (2015). [CrossRef]
7. G. M. Gale, M. Cavallari, T. J. Driscoll, and F. Hache, “Sub-20-fs tunable pulses in the visible from an 82-MHz optical parametric oscillator,” Opt. Lett. 20(14), 1562–1564 (1995). [CrossRef]
8. S. Witte, R. Th. Zinkstok, A. L. Wolf, W. Hogervorst, W. Ubachs, and K. S. E. Eikema, “A source of 2 terawatt, 2.7 cycle laser pulses based on noncollinear optical parametric chirped pulse amplification,” Opt. Express 14(18), 8168–8177 (2006). [CrossRef]
9. D. Herrmann, L. Veisz, R. Tautz, F. Tavella, K. Schmid, V. Pervak, and F. Krausz, “Generation of sub-three-cycle, 16 TW light pulses by using noncollinear optical parametric chirped-pulse amplification,” Opt. Lett. 34(16), 2459–2461 (2009). [CrossRef]
10. T. Stanislauskas, R. Budriunas, R. Antipenkov, A. Zaukevicius, J. Adamonis, A. Michailovas, L. Giniunas, R. Danielius, A. Piskarskas, and A. Varanavicius, “Table top TW-class OPCPA system driven by tandem femtosecond Yb:KGW and picosecond Nd:YAG lasers,” Opt. Express 22(2), 1865–1870 (2014). [CrossRef]
11. F. Batysta, R. Antipenkov, J. Novák, J. T. Green, J. A. Naylon, J. Horácek, M. Horácek, Z. Hubka, R. Boge, T. Mazanec, B. Himmel, P. Bakule, and B. Rus, “Broadband OPCPA system with 11 mJ output at 1 kHz, compressible to 12 fs,” Opt. Express 24(16), 17843–17848 (2016). [CrossRef]
12. M. Schulz, R. Riedel, A. Willner, T. Mans, C. Schnitzler, P. Russbueldt, J. Dolkemeyer, E. Seise, T. Gottschall, S. Hädrich, S. Duesterer, H. Schlarb, J. Feldhaus, J. Limpert, B. Faatz, A. Tünnermann, J. Rossbach, M. Drescher, and F. Tavella, “Yb:YAG Innoslab amplifier: efficient high repetition rate subpicosecond pumping system for optical parametric chirped pulse amplification,” Opt. Lett. 36(13), 2456–2458 (2011). [CrossRef]
13. L. E. Zapata, H. Lin, A.-L. Calendron, H. Cankaya, M. Hemmer, F. Reichert, W. R. Huang, E. Granados, K.-H. Hong, and F. X. Kärtner, “Cryogenic Yb:YAG composite-thin-disk for high energy and average power amplifiers,” Opt. Lett. 40(11), 2610–2613 (2015). [CrossRef]
14. J. Novák, J. Green, T. Metzger, T. Mazanec, B. Himmel, M. Horáček, Z. Hubka, R. Boge, R. Antipenkov, F. Batysta, J. Naylon, P. Bakule, and B. Rus, “Thin disk amplifier-based 40 mJ, 1 kHz, picosecond laser at 515 nm,” Opt. Express 24(6), 5728–5733 (2016). [CrossRef]
15. R. Budriūnas, T. Stanislauskas, J. Adamonis, A. Aleknavičius, G. Veitas, D. Gadonas, S. Balickas, A. Michailovas, and A. Varanavičius, “53 W average power CEP-stabilized OPCPA system delivering 5.5 TW few cycle pulses at 1 kHz repetition rate,” Opt. Express 25(5), 5797–5806 (2017). [CrossRef]
16. B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchik, B. W. Shore, and M. D. Perry, “Nanosecond-to-femtosecond laser induced breakdown in dielectrics,” Phys. Rev. B 53(4), 1749–1761 (1996). [CrossRef]
17. J. Fülöp, Z. Major, B. Horváth, F. Tavella, A. Baltuska, and F. Krausz, “Shaping of picosecond pulses for pumping optical parametric amplification,” Appl. Phys. B 87(1), 79–84 (2007). [CrossRef]
18. D. Gaudiosi, A. Lytle, P. Kohl, M. Murnane, H. Kapteyn, and S. Backus, “11-W average power Ti:sapphire amplifier system using down chirped pulse amplification,” Opt. Lett. 29(22), 2665–2667 (2004). [CrossRef]
19. L. Indra, F. Batysta, P. Hříbek, J. Novák, Z. Hubka, J. Green, R. Antipenkov, R. Boge, J. Naylon, P. Bakule, and B. Rus, “Picosecond pulse generated supercontinuum as a stable seed for OPCPA,” Opt. Lett. 42(4), 843–846 (2017). [CrossRef]
20. A. Schwarz, M. Ueffing, Y. Deng, X. Gu, H. Fattahi, T. Metzger, M. Ossiander, F. Krausz, and R. Kienberger, “Active stabilization for optically synchronized optical parametric chirped pulse amplification,” Opt. Express 20(5), 5557–5565 (2012). [CrossRef]
21. F. Batysta, R. Antipenkov, J. Green, J. Naylon, J. Novák, T. Mazanec, P. Hříbek, C. Zervos, P. Bakule, and B. Rus, “Pulse synchronization system for picosecond pulse-pumped OPCPA with femtosecond-level relative timing jitter,” Opt. Express 22(24), 30281–30286 (2014). [CrossRef]
22. V. Pyragaite, A. Stabinis, R. Butkus, R. Antipenkov, and A. Varanavičius, “Parametric amplification of chirped optical pulses under pump depletion,” Opt. Commun. 283(6), 1144–1151 (2010). [CrossRef]
23. L. J. Waxer, V. Bagnoud, I. A. Begishev, M. J. Guardalben, J. Puth, and J. D. Zuegel, “High-conversion-efficiency optical parametric chirped pulse amplification system using spatiotemporally shaped pump pulses,,” Opt. Lett. 28(14), 1245–1247 (2003). [CrossRef]
24. S. Witte and K. Eikema, “Ultrafast optical parametric chirped-pulse amplification,” IEEE J. Sel. Top. Quantum Electron. 18(1), 296–307 (2012). [CrossRef]
25. J. Adamonis, R. Antipenkov, J. Kolenda, A. Michailovas, A. P. Piskarskas, A. Varanavičius, and A. Zaukevičius, “Formation of flat-top picosecond pump pulses for OPCPA systems by second harmonic generation,” Lith. J. Phys. 52(3), 193–202 (2012). [CrossRef]
26. J. Pupeikis, P.-A. Chevreuil, N. Bigler, L. Gallmann, C. R. Phillips, and U. Keller, “Water window soft x-ray source enabled by a 25 W few-cycle 2.2 µm OPCPA at 100 kHz,” Optica 7(2), 168–171 (2020). [CrossRef]
27. P. Mackonis and A. M. Rodin, “Laser with 1.2 ps, 20 mJ pulses at 100 Hz based on CPA with a low doping level Yb:YAG rods for seeding and pumping of OPCPA,” Opt. Express 28(2), 1261–1268 (2020). [CrossRef]
28. J. Moses, C. Manzoni, S. Huang, G. Cerullo, and F. Kärtner, “Temporal optimization of ultrabroadband high-energy OPCPA,” Opt. Express 17(7), 5540–5555 (2009). [CrossRef]
