Picosecond laser amplification system with 93 W high average power Runwu Peng * , Lin Guo, Xiaofu Zhang, Fangqin Li, Qianjin Cui, Yong Bo, Qinjun Peng, Dafu Cui, Zuyan Xu Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, China Received 22 July 2007; received in revised form 15 December 2007; accepted 16 January 2008 Abstract A high average power picosecond laser amplification system with diode-end-pumped Nd:YVO 4 and diode-side-pumped Nd:YAG is described. Laser with power up to 92.7 W, repetition frequency of 73.3 MHz, pulse duration of 26.5 ps, and beam quality of M 2 < 3.5 is generated in the amplification system. Thermal-birefringence-induced depolarization in the Nd:YAG rod laser head amplifier is mea- sured to be 21.9 W though birefringence compensation is performed. Ó 2008 Elsevier B.V. All rights reserved. PACS: 42.55Xi; 42.60By; 42.60Da Keywords: Picosecond laser; Amplification; Diode-pumped; Depolarization 1. Introduction Lasers with high power, high beam quality, and short pulse duration have been found widely used in many laser applications such as high-precision micro-machining, laser display, efficient harmonic generation in nonlinear media, and laser direct imaging in the printed circuit industry. Thus, passively mode-locked solid-state laser oscillator and solid-state laser amplifier that can generate such char- acteristic pulsed lasers have been investigated in lots of papers in detailed [1–9]. By employing a commercial mode-locked diode-pumped Nd:YVO 4 seed laser and a Lightwave Electronics direct-coupled pump laser head which consists of a Nd:YAG laser rod directly side pumped with a 40-W 1-cm-long laser diode bar, 9.3 W laser with 20.5 ps in pulse duration has been achieved by Dymott and Weingarten [4]. Eighty one watt laser with pulse dura- tion of 300 ps have been realized by using amplifier consist- ing of commercial diode-pumped 4-mm-diameter, 116-mm- long and 6-mm-diameter, 146-mm-long Nd:YAG rod laser modules [7]. To generate higher output power to meet many applications, such laser systems are studied further nowadays. In this paper, we present a high average power picosec- ond laser amplification system consisting of two single-pass Nd:YVO 4 amplifiers and four single-pass Nd:YAG rod laser heads amplifiers. Nd:YVO 4 is chosen in the oscillator served as seed laser and in the former two amplifiers because it is a laser crystal for reducing the stable CW mode-locking threshold, realizing compact, and high opti- cal efficiency, thanks to its large stimulated-emission cross section. Nd:YAG is used in the following four amplifiers because of its good thermal conductivity and high stress fracture limit. The combination of the advantages of Nd:YVO 4 and Nd:YAG in the system helps us to achieve a high average output power. 2. Experiment setup Our high average power picosecond laser amplification system consists of two single-pass diode-end-pumped Nd:YVO 4 amplifiers and four diode-side-pumped 0030-4018/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2008.01.024 * Corresponding author. Tel.: +86 10 82649352. E-mail address: pengrunwu@163.com (R. Peng). www.elsevier.com/locate/optcom Available online at www.sciencedirect.com Optics Communications 281 (2008) 2879–2882