# Compact 50 W All-Solid-State Picosecond Laser System at 1 kHz
###### Abstract  
Compact, stable, high-power and high repetition rate picosecond laser systems are excellent sources for optical parametric chirped pulse amplification systems and laser satellite ranging systems. Compared with the traditional complex high-power amplifier, this article reports a compact high-power picosecond laser system at a repetition rate of 1 kHz based on Nd:YAG bulk crystal. The thermal lens effect limits the regenerative amplifier to directly output higher energy. For this reason, multi-stage traveling-wave amplifiers are usually used to gradually increase the laser pulse energy. So as to achieve a compact structure, a regenerative amplifier that can output higher power at 1 kHz is designed in the laser system. The regenerative amplifier can output the power of 6.5 W at the pump power of 41.5 W; the beam quality of M\({}^{2}\) factor was about 1.3. A more flexible thermal depolarization compensation structure is applied in the side-pumped amplifier, which can effectively compensate for thermal lens effect and thermal depolarization at different pump powers. Finally, the laser pulse can achieve an output power higher than 50 W at 1 kHz after passing through an end-pumped traveling-wave amplifier and a side-pumped traveling wave amplifier. p 202020020 Although the beam quality of the side-pumped amplifier is not good, the side-pumped amplifier can achieve higher output power. Usually end-pumped and side-pumped hybrid amplifiers are used to obtain laser pulses with high power and high beam quality. For the purpose of obtaining higher output power, the higher population inversion density of gain medium is required. The high population inversion density usually derives from higher pumping power. Thus, reducing the thermal effect and thermal management are the key issues in a high-power diode-pumped solid-state laser. In recent years, various types of high-power picosecond laser systems via different cooling technologies have been constructed. The high-power laser systems via rod gain medium pulses with 75 mJ and 64 pS at 300 Hz [5], 80 mJ and 50 pS at 1 kHz [6], 130 mJ and 95 pS at 1 kHz [7], 64.8 mJ and 15 ps at 1 kHz [8], 363 mJ and 63 ps at 100 Hz [9], 50 mJ and 100 ps at burst mode 1 kHz [10], and with 131.83 mJ and 16.9 ps at 496.85 kHz were demonstrated with the gain mediums of Nd:YAG or Nd:YVO\({}_{4}\)[11]. In the above-mentioned systems, the output power of the regenerative amplifier stage is usually about 2 W at 1 kHz. In order to achieve higher output power, three or more traveling-wave amplifiers are usually required. The Yb-doped crystal laser is usually a three-level system, which requires higher energy to generate population inversion compared to the four-level system. At the same time, the Yb-doped crystal usually has a wider gain bandwidth, so it can be used in chirped pulse amplification (CPA) system to output high-energy and ultra-short laser pulses. In order to solve the heat dissipation problem of the Yb-doped crystal, take the Yb:YAG crystal as an example, which can usually be made into a thin disk to reduce the influence of the thermal effect. Based on thin-disk technology and chirped pulse amplification technology, pulses with 300 mJ and 1.8 ps at 100 Hz [12], 90 mJ and 1.2 ps at 1 kHz [13], and with 200 mJ and 1.1 ps at 5 kHz were reported [14]. The thin-disk laser systems generally can output higher energy at high repetition rate, however the CPA system is more complex and the price of a thin-disk module is extremely high. Bulk material laser systems usually have higher efficiencies and simpler structures, thus making them more attractive to many application fields. In some outdoor applications of high-power picosecond lasers, the laser system requires a smaller volume, which is also more conducive to the stability of the laser system. So as to further simplify the structure, it is necessary to increase the output power of each stage amplifier.