Abstract

We demonstrate efficient conversion of a laser beam of poor spatial quality into a nearly diffraction-limited beam at the pump frequency. The method is based on Stimulated light scattering in liquids pumped with a Bessel beam [1,2]. The input beam (Fig. 1) is transformed by an axicon to a Bessel beam which is imaged into a liquid cell. With a broadband (1.0 cm^–1) pump at 532nm from a Q-switched Nd:YAG laser and methanol as the scattering medium, a high quality Gaussian beam is generated in the forward direction along the cone axis of the Bessel beam (see Fig. 2). Its spectrum shows a bandwidth of 1.5cm^–1 broadened to the Stokes side and has a maximum at pump frequency. We attribute this effect to Stimulated Rayleigh-Wing Scattering in a non collinear scattering geometry: the angular plane waves of the Bessel beam transfer energy to the on-axis Stokes beam and, correspondingly, a cone of molecular orientation waves is generated in the medium.

© 1996 IEEE