Recent publications have shown that electron impact collisions are more important than Penning collisions in populating the upper level of the 441.6 nm transition of He-Cd+ lasers operated as positive column discharges. The authors present evidence that this is not the case in hollow cathode discharges.
Gas temperatures along the axis of a hollow-cathode He-Cd laser have been measured. The effect of gas temperature variations on calculations of both the excited-state number densities and the heavy-body Penning collision rates are assessed. Implications on the gas kinetics of these discharge types, in particular, on the role of Penning collisions in populating the 5s2 2D5/2 level of the cadmium ion are discussed.
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...
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