Frequency shift and asymmetric line shape of the fourth anti-Stokes component from a hydrogen Raman shifter

We have measured the spectral properties of the fourth anti-Stokes component of the output of a pressurized, molecular hydrogen, Raman shifter pumped by the intense output of a frequency-doubled narrowband pulsed dye laser. All the observed line shapes are asymmetric, with full widths at half-maximum ranging from 0.3 to 0.8 cm(-1). The spectral peak of the Raman-shifted light varies linearly with the intensity of the pump light and is given by sigma(rho,I) = sigma(rho) + AI. The previously measured density-dependent Stokes shift is sigma(rho), the intensity of the laser is I, and A is 1.5 +/- 0.2 cm(-1)/(TW/cm(2)). The electric field-induced shift and asymmetric line shape limit the accuracy and resolution of spectroscopic measurements made with light from a hydrogen Raman shifter. We propose that these observations may be explained by the ac Stark effect in the Raman shifting medium.