IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 41 (2008) 135112 (6pp) doi:10.1088/0022-3727/41/13/135112 2.54 W 1535 nm KTiOAsO 4 optical parametric oscillator within a diode-side-pumped acousto-optically Q-switched Nd : YAG laser Zhaojun Liu 1 , Qingpu Wang 1 , Xingyu Zhang 1 , Zejin Liu 1 , Jun Chang 1 , Hao Wang 1 , Shuzhen Fan 1 , Shutao Li 1 , Shuaishuai Huang 1 , Wenjia Sun 1 , Guofan Jin 1 , Xutang Tao 2 , Shaojun Zhang 2 and Huaijin Zhang 2 1 School of Information Science and Engineering, Shandong University, Ji’nan, Shandong 250100, People’s Republic of China 2 State Key Laboratory of Crystal Materials, Shandong University, Ji’nan, Shandong 250100, People’s Republic of China E-mail: xyz@sdu.edu.cn Received 15 April 2008 Published 12 June 2008 Online at stacks.iop.org/JPhysD/41/135112 Abstract We report a nanosecond singly resonant intracavity optical parametric oscillator (OPO) emitting at 1535 nm. This OPO is based on a type II non-critically phase-matched KTiOAsO 4 (KTA) crystal. A diode-side-pumped acousto-optically Q-switched Nd : YAG laser is used as the pumping source. With a laser diode power of 96.3 W and a pulse repetition rate of 10 kHz, we obtain a signal power of 2.54W, corresponding to an optical-to-optical conversion efficiency of 2.6%. This is the highest efficiency reported for intracavity KTA OPOs with diode-side-pumping configurations. The pulse width is 5.01 ns and the peak power is 50.7 kW. The stability of the signal power is measured to be better than 3% during 2 h operation. (Some figures in this article are in colour only in the electronic version) 1. Introduction Optical parametric oscillators (OPOs) have established themselves as efficient, reliable, solid-state sources of tunable radiation. Of all kinds of OPOs, those made of KTiOPO 4 (KTP) crystals have been extensively studied for use in parametric conversion of Nd-doped lasers to longer wavelengths [1–4]. One of the major advantages of the OPOs based on KTP and its isomorphs is the ability to operate with the non-critical phase matching (NCPM) scheme. The large acceptance angle for NCPM permits efficient OPO operation even with multi-transverse-mode pumping lasers. KTiOAsO 4 (KTA), one of the isomorphs of KTP, is also an efficient nonlinear crystal. It has higher transmission in the 3–5 μm region than KTP and does not have the absorption feature seen in KTP near 3.4 μm[5]. This makes KTA more attractive than KTP in high power OPOs. As for laser gain materials, Nd : YAG, Nd : YVO 4 , Nd : GdVO 4 , Nd : YLF and Nd : YAP have been widely used to generate nanosecond (ns) or picosecond (ps) laser pulses and Ti : sapphire has been selected for femitosecond (fs) or ps lasers. For extracavity KTA OPOs, Ti : sapphire lasers and several Nd-doped lasers were used as the pumping sources [6–13]. Lasers made of Ti : sapphire crystals were used to produce fs and ps pulses in [6–8] and [9], respectively. Nd : YVO 4 laser (ps), Nd : YAG lasers (ns) and Nd : YLF lasers (ns) were selected in [10], [11, 12] and [13], respectively. For intracavity OPOs, several combinations of Nd-doped crystals and KTA crystals have been reported [14–17]. Nd : YLF crystals and KTA crystals cut at different angles were used in [14, 15] to obtain tunable laser sources. A Nd : YAP crystal and an x -cut KTA crystal were employed in [16] for both 1.5 and 3.5 μm outputs. A Nd : YVO 4 crystal and an x -cut KTA crystal were used in [17] to generate 1.5 μm laser pulses. 0022-3727/08/135112+06$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK