Enhanced efficiency of UV second harmonic and sum frequency generation from copper vapor lasers

Abstract

Enhanced efficiency for nonlinear second harmonic and sum frequency generation in 0-BBO from the two copper vapor laser (CVL) outputs (511 and 578 nm) is reported. Over 460 mW UV output at 255 nm (SHG of 511 nm) and 271 nm (SFG), and up to 300 mW at 289 nm (SHG of 578 nm) have been obtained with wall plug efficiencies up to 0.016% for a 16 W CVL with an M = 26.5 off-axis unstable cavity.HERE is an increasing demand for ultraviolet laser T sources of moderate average power ( > 1 W ) for industrial applications such as photolithography [ 11. Copper vapor lasers with high average power (up to 100 W ) at high pulse repetition rates ( -10 kHz) and relatively high wall plug efficiency (up to 1 % ) in the green (510.6 nm) and the yellow (578.2 nm) are now widely available commercially. Second harmonic and sum frequency generation (SHG and SFG) of CVL output therefore represents an attractive approach to UV source development. However, doubling efficiencies from CVL outputs have been disappointing due to the difficulties of achieving high focal power densities in the nonlinear medium resulting from the poor beam quality from the CVL.Use of high magnification unstable optics and injection seeding techniques have recently led to considerable improvements in CVL beam quality, with consequent improvements in the nonlinear conversion efficiency. Kuroda et al.[2] have reported over 230 mW at 255.1 nm by SHG in 0-BBO from the 510.6 nm output of a 10 W CVL and Naylor et al. [3] have reported up to 630 mW at 255.1 nm based on a 100 W injection seeded CVL. In earlier experiments in our own laboratory with a 7 W CVL we have obtained similar SHG efficiencies in BBO and KDP, and reported sum frequency generation ( 5 10.6 + 578.2 nm) at 271.2 nm with conversion efficiencies comparable to SHG 141.Further improvements in SHG and SFG efficiencies require careful attention to the design of the CVL cavity to achieve a higher fraction of the output power within the high quality (low divergence) portion of the beam, and to delivery optics in the nonlinear conversion arrangement. We now report recent experiments in SHG and SFG based Manuscript received December 7, 1989. The authors are with the Centre for Lasers and Applications, Macquarie University, NSW 2109, Australia. IEEE Log Number 9037373. Polarising Cube Polarising cube Aoerture (C) Fig. 1, (a) On-axis unstable resonator. (b) Off-axis unstable resonator. (c) Experimental arrangement for generation and detection of SHG and SFG. on a higher power ( 16 W ) CVL and aimed at optimizing CVL resonator design and focusing geometries. SHG (255 nm) and SFG (271 nm) powers of 460 and 465 mW, respectively, have been achieved at conversion efficiencies from the nonASE component of the CVL beam up to 9.6%and wall plug efficiency -0.016%.The experimental arrangement is shown in Fig. 1. The CVL is fitted with either an on-axis edge-coupled unstable cavity (positive branch confocal) [ Fig. l(a)] or an off-axis cavity of the same type [ Fig. l(b)] [ 5 ] . The resonators are in each case formed by a hig...

A Wavelength Tunable Q-Switched Erbium-Doped Fiber Laser with Fiber Bragg Grating Mirrors

“…Taking into account the losses in the lens L2 and the prism P R~ (estimated at about 20%) 7 approaches 5% in this case. This result is close to the theoretical predictions in [l] and the experimental results in [3] given for CVL.…”