Acta Photonica Sinica, Volume. 52, Issue 9, 0914002(2023)

Tunable Repetition-rate High Power Picosecond Green Laser

Sizhi XU1, Ying XIA1, Yubo GAO1,2, Xing LIU1,2、*, Deqin OUYANG1,2, Yewang CHEN1,2, Xu WU1,2, Fanghua XU3, Li GUO3, Junqing ZHAO1, Chunyu GUO4, Qitao LV1,2,3, and Shuangchen RUAN1,2、*
Author Affiliations
  • 1Key Laboratory of Advanced Optical Precision Manufacturing Technology of Guangdong Higher Education Institutes,Shenzhen Technology University,Shenzhen 518118,China
  • 2Sino-german College of Intelligent Manufacturing,Shenzhen Technology University,Shenzhen 518118,China
  • 3Han's Laser Technology Industry Group Co. Ltd.,Shenzhen 518103,China
  • 4Shenzhen Key Laboratory of Laser Engineering,College of Physics and Optoelectronic Engineering,Shenzhen University,Shenzhen 518060,China
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    In this paper, an 1 064 nm, 148.7 W, 8 ps laser is obtained through a multi-stage end-pumped Nd:YVO4 solid-state laser amplification system. Further a 1mm-diameter spot is coupled to a LBO crystal for frequency doubling, and a 95 W, 6.43 ps laser output is obtained at 532 nm, with a tunable Pulse Repetition Frequency (PRF) of 500 kHz~4 MHz. The Nd∶?YVO4 Master Oscillator Power Amplifier (MOPA) consists of a high-power oscillator stage, fiber pre-amplifier and four end-pump amplifier stages. The seed is an all-fiber laser mode-locked by SESAM with a pulse duration of 7.8 ps and PRF of 20 MHz. The Acoustic Optical Modulator (AOM) is used for reducing the PRF to realize a higher peak power. The end-pump power amplifier is a four-stage free-space bulk amplifier based on neodymium-doped yttrium vanadate (Nd∶?YVO4) crystals for high-efficiency frequency conversion. It has a high polarization-dependent gain spectrum due to the birefringence of the uni-axial YVO4 crystal. Each amplifier is comprised of a 0.3% doped a-cut Nd∶?YVO4 crystal having dimensions of 4 mm×4 mm×15 mm and is mounted on a water-cooled heat sink. All amplifiers are end-pumped by a fiber-coupled 878.6 nm (400 μm core, NA=0.22) Laser Diode (LD), instead of conventional 808 nm LD, to reduce the degradation of the beam quality by thermal effects. The first amplifier stage is a double-pass configuration and increases the signal average power to 13 W for a 65 W pump light, while the second amplifier stage is a single-pass and scales up to 56 W of average power for a 115 W pump light. To match the amplified light with the pump light of the third stage, a lens of 80 mm focal length is added between the second stage and the third stage. Finally, 56 W, 2 MHz infrared (1 064 nm) 8.08 ps output with M2<1.5 is obtained. Then, the 56 W infrared picosecond laser is used as the source of the pre-amplification, and after shaping, it is focused to the third and fourth-stage amplifying module. This module uses two 115 W LD pumps with a center wavelength of 878.6 nm to pump two Nd∶YVO4 crystals. The seeding picosecond laser passes through the third crystal and is then deflected by a dichroic mirror (DM3) to the fourth crystal for further power amplification. An output power of 148.7 W is achieved, and the beam quality factor of the amplified pulses is MX2=1.72 and MY2=2.18. along horizontal and vertical directions, respectively.After shaping the output, a 1 mm-diameter spot is coupled to LBO crystal for frequency doubling. The highest output power is 95 W at 2 MHz PRF, corresponding to the best second harmonic conversion efficiency of 65%. The conversion efficiency is expected to be further improved with the fundamental frequency optical power, the beam quality factor is MX2=1.27, MY2=1.42. At the highest average power output, the stability of the system is observed for more than 6 hours, and the power fluctuation RMS is lower than 0.8%. In addition to achieve the highest frequency-doubling conversion efficiency, the effect of the fine regulation of the temperature of the LBO crystal on the optimal critical phase matching condition of the crystal is also studied. The laser system has the advantages of simple optical path, high average power, good beam quality, tunable repetition frequency and high stability. It is an ideal fundamental frequency light source for high-power ultraviolet and deep ultraviolet lasers, and has important applications in the fields of industrial processing and scientific research. It is expected to achieve more efficient and can be utilized for high-quality processing fields such as battery welding, and hard and brittle materials processing.

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    Sizhi XU, Ying XIA, Yubo GAO, Xing LIU, Deqin OUYANG, Yewang CHEN, Xu WU, Fanghua XU, Li GUO, Junqing ZHAO, Chunyu GUO, Qitao LV, Shuangchen RUAN. Tunable Repetition-rate High Power Picosecond Green Laser[J]. Acta Photonica Sinica, 2023, 52(9): 0914002

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    Paper Information

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    Received: Mar. 16, 2023

    Accepted: May. 6, 2023

    Published Online: Oct. 24, 2023

    The Author Email: LIU Xing (liuxingstart123@163.com), RUAN Shuangchen (scruan@sztu.edu.cn)

    DOI:10.3788/gzxb20235209.0914002

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