LD side-pumped intracavity frequency-doubled high power Nd: YAG green laser based on acousto-optic Q-switch

Abstract

A highly efficient and high power green laser generated by intracavity frequency doubling of a diode-sidepumped Q-switched Nd: YAG laser has been demonstrated. In the simple L-shaped cavity geometry, the maximum green output power of 28.5 W was obtained with a pulse width of 95 ns at a pulse repetition rate of 10 kHz by using a LBO crystal for frequency doubling,corresponding to a conversion efficiency of 11% from diode pump power to pulse green power. At a pulse repetition rate of 1 kHz, 6.9 mJ of pulse energy,25 ns of pulse duration and 276 kW of peak power were obtained. All-solid-state green lasers with high average power (~1 0 W) and high pulse repetition frequency rate have been required for various applications in industry,medicine,scientific research and entertainments Llj. Some typical applications include processing of materials such as copper or silicon, efficient pumping source of Ti:Sappphire lasers and medical equipments. Intracavity frequency doubling of an acousto-optic (A O) Q-switched Nd: YAG laser is an approach to achieve high efficient green laser. In recent years, much work has progressed in high-power green laser. For example, a maximum average 532-nm output power of 138 W was generated by Konno et al F2~ with a pump-to green conversion efficiency of 17.50//00 in design of two pump heads. In order to achieve efficient non-linear frequency conversion, excellent beam quality and high peak power are required. Moderate average power with high beam quality have been demonstrated in Nd. YAG using end-pumping [3~. However,it is difficult to obtain an average power over 10 W with good beam quality and peak power without increasing system complexity Fq . A simpler means to achieve solid-state lasers is to use diode-side-pumping. In this work, we present highly efficient generation of green laser with a power of 28. 5 W by intracavity frequency doubling of a side-pumped Qswitched Nd-YAG laser with a pump-to-green conversion efficiency of Fig. 1 shows the experimental geometry of three-mirror L-shape laser cavity for green beam generation. It consists of a pump head of the gain crystal N d : Y A G rod side -pumped by diode laser bars , an optical nonlinear . This work was supported by the National Natural Science Foun dation of China(Grant No:60478009) * * E-mail:jlhe@icm. sdu. edu. cn LBO crystal for second harmonic generation ( S H G ) , a n d an acousto~optic (A-O) Q-switcher. The Nd. YAG host crystal used here has a concentration 0.6 ~ of Nd 3+ and with a dimension of ~ 4 X 60 mm 3. The side-pump source used here is an 808-nm bar coupled laser-diode with a continuous-wave (CW) output power of 300 W under the maximum incident current of 20 A. The three mirror cavity is composed of two mirror M1 and M2, and output coupler Mcc. M1 is a concave mirror with a curvature radius of 100 cm and M2 is a flat mirror. The two mirrors are coated with a high reflection R at oscillating wavelength (R~99.80/00 at 1 064 nm) and second harmonic (R~99.0~ at 532 nm) on the inside surface. Moc is a flat mirror with a h...