Abstract

The tuning-range increase of the excimer laser radiation by stimulated Raman scattering is quite useful in many industrial and scientific application fields as in differential-absorption lidar systems for stratospheric and troposheric ozone measurements [1]. Stimulated rotational Raman scattering (SRRS) in H₂ has recently been investigated with a XeCl laser beam to increase the tuning-range of excimer lasers [2]. The Raman shift in H₂ is 4155.21 cm^-1 and 588 cm^-1 for vibrational and rotational scattering, respectively and then, rotational Raman scattering provides Stokes lines more closely spaced to the XeCl line (308 nm) with respect to vibrational Raman scattering. It is shown in [2] that energy conversion efficiencies to the first rotational Stokes S₀₁ (314 nm) of about 35% were obtained in 30 bar of H₂ by focusing a good-optical-quality XeCl laser beam of relatively low energy (14 mJ) and circularly polarised. The use of a focusing lens of 15-cm focal length was peculiar to get such high conversion efficiencies. In fact, with a circularly polarised pump beam a high-angle focusing geometry allowed to get only rotational Raman scattering as a consequence of gain suppression effects on vibrational Raman scattering, whereas a low-angle focusing geometry provided only vibrational Raman transitions.

© 1998 IEEE