Tunable Raman up-converter as a coherent generator

This experimental paper describes the operation of simple coherent laser-generated tunable source of medium power (1 to 10⁴watts) in the visible spectrum (15 600 to 19 400 cm^-1) with high repetition rate (1 to 20 pps). A broad-band source is created by a -switched Nd:YAG laser beam in a cell containing carbon disulphide, by a complex process involving multiple-order stimulated Raman scattering, self-focusing, and parametric line broadening. The spectrum of this source extends over more than 4000 wavenumbers in the infrared. It presents broad intensity peaks at distances from the laser line equal to multiples of the CS2Raman shift, and an intense continuum. This source is selectively up-converted by the laser beam itself in a nonlinear lithium niobate crystal with both beams collinear. Temperature adjustment of the crystal acts on the phase-matching condition and provides continuous tuning from 0.515 μ at - 100° C to 0.640 μ at 375° C. The linewidth is less than 11 cm^-1. This simple tunable source includes no critical components and does not put stringent requirements on crystal quality. The up-converter also provides a good experimental method for studying the IR spectra of pulsed sources.