Abstract

It is well known that two primary laser beams at frequencies ω₁, ω₂ can be combined in a nonlinear mixing crystal to generate an output beam at the sum-frequency ω₃ = ω₁ + ω₂, provided that the wavelength λ₃ is, roughly speaking, greater than ≃200 nm. At shorter wavelengths, severe problems arise, associated both with the limited VUV transmission of crystalline materials, and with the limited extent to which three-wave mixing processes that result in VUV output can be phase-matched. However, it has long been recognized that with use of a higher-order non-linear process, four-wave difference-frequency mixing (ω₃ = 2ω1 – ω₂) in gases, one is no longer prevented by the two above-mentioned effects from generating coherent light at wavelengths shorter than 200 nm. In a recent investigation,¹ femtosecond-time-scale VUV pulses were generated by the second method discussed above. For the input beam at ω₁, 180-fsec, ≃308-nm pulses that had been amplified in a standard XeCl discharge excimer gain module were employed. For the input beam at near-IR pulses (pulsewidth 150 fsec, energy 150 μJ, wavelength ≃757 nm) were used. The input beam wavelength, λ₂ was chosen so that the output beam wavelength, λ₃ would be at 193 nm, i.e., at the ArF excimer wavelength. The mixing medium employed was 1 atm. of Xe gas.

© 1993 Optical Society of America