Ultraintense ultrashort lasers are widely used in strong-field physics,such as high harmonic generation[
Laser & Optoelectronics Progress, Volume. 58, Issue 17, 1736001(2021)
[in Chinese]
A diode pumped high energy Yb∶YAG rod regenerative amplifier was demonstrated with a maximum energy of 22.3 mJ, excellent energy stability (~0.8% root mean square), and beam quality (M2 < 1.2) at 10 Hz repetition rate. To the best of our knowledge, this is the highest energy so far obtained by a Yb∶YAG rod regenerative amplifier.
1 Introduction
Ultraintense ultrashort lasers are widely used in strong-field physics,such as high harmonic generation[
Yb∶YAG gain-medium-based lasers have rapidly gained prominence in the past two decades due to their excellent spectral,thermal,and mechanical characteristics,such as long storage lifetime,large emission cross-section [
A repetition frequency of 10 Hz can meet requirements for many strong-field physical experiments[
Figure 1.Conceptual design of Yb∶YAG rod amplifier and nonlinear-compression-based TW laser system
In this study,a high energy,diode-pumped Yb∶YAG rod regenerative amplifier is demonstrated. The nanosecond laser output energy was as high as 22.3 mJ,and the root-mean-square(RMS)energy variation was as small as 0.8%,with M2 < 1.2 near the diffraction-limited beam. To the best of our knowledge,this is the highest energy ever obtained by a Yb∶YAG rod regenerative amplifier.
2 Experimental setup
Figure 2.Experimental setup
In terms of cavity design,the length of the resonant cavity was 2.2 m. The round-trip time of photons in the cavity was 14.7 ns. The laser rod was the symmetric center of the cavity. On each side of the crystal are two large-curvature-radius concave mirrors(right-side is M1 and M3;left-side is M4 and M6)and one large-curvature-radius convex mirror(right-side is M2;left-side is M5),making the beam-radius variation less than 3.4% within the range of -200 mm to 200 mm from the symmetry center of the cavity. To avoid optical damage,the cavity was designed with a 1 mm mode diameter and a 1.9 mm PC side diameter,having a low damage threshold. The mode diameter was optimized for maximum output energy with a pump-to-mode diameter ratio of 0.8. To control the amplification passes,a quarter-wave plate(QW),thin-film polarizer(TFP),and PC were used for optical switching. To separate the input and output beams,a Faraday rotator(FR),half-wave plate(HW),and TFP were employed.
3 Results
The system was first characterized in a free-running(continuous-wave)condition,and then the seed was injected into the regenerative amplifier.
3.1 Free-running operation
The regenerative cavity was adjusted and optimized under a free-running condition with quasicontinuous wave(QCW)pumping(10 Hz,
Figure 3.Output energy as a function of absorbed pump energy for free running (inset: near-field beam profile with 225 mJ absorbed pump energy and 1.5 ms pump pulse width)
3.2 Injected seed operation
With the optimized cavity,the seed was injected,and the PC was enabled.
Figure 4.Results. (a) Round-trip time and output energy with 1.5 ms pump pulse width at 10 Hz; (b) intracavity pulse-amplification evolution
Figure 5.Pulse waveform. (a) Temporal pulse shape of regenerated output; (b) input seed spectrum, Q-switched spectrum, and amplified-pulse spectrum
Figure 6.Results. (a) M2 factor of output laser beam (inset: far-field beam profile); (b) 2 h output-energy stability test result
4 Conclusion
In summary,a diode-pumped Yb∶YAG rod regenerative amplifier was developed. Owing to a QCW pump and progressive cavity design,the regenerative amplifier boosted the seed from nanojoules to 22.3 mJ with high energy stability(RMS variability <0.8%)and obtained both a near-diffraction-limited beam(M2 <1.2)and 0.8 nm Q-switched spectrum bandwidth. Future works include enlarging the cavity-mode diameter,increasing the pump power,and injecting a broadband chirped seed,thereby increasing the energy to 50 mJ with a 0.8 nm chirped pulse. Afterward,a cascaded two-stage compression would be performed;thus,a low-cost TW-class laser is realizable.
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Wentao Zhu, Huijun He, Jun Yu, Qingdian Lin, Xiaoyang Guo, Cangtao Zhou, Shuangchen Ruan. [J]. Laser & Optoelectronics Progress, 2021, 58(17): 1736001
Received: Jun. 26, 2021
Accepted: Jul. 7, 2021
Published Online: Sep. 15, 2021
The Author Email: Guo Xiaoyang (guoxiaoyang@sztu.edu.cn), Zhou Cangtao (zhoucangtao@sztu.edu.cn), Ruan Shuangchen (ruanshuangchen@sztu.edu.cn)