Generation of tunable infrared radiation by stimulated electronic hyper-Raman-effect in strontium vapour

Tunable infrared radiation in the wavelength range of 16 um was generated by stimulated electronic hyper-RAMAN scattering in atomic strontium vapour using a pulsed dye laser. A nearby two-photon resonance was used to enhance the conversion efficiency. The actual infrared output was, however, much less than estimated from perturbational calculations. In addition, the observed dependence of the STOKES energy on the power of the dye laser differed drastically from the expectation of perturbation theory. There is, however, quite good agreement between experiment and a non-perturbational description of the process, which had been stimulated by the present work. According to this theory, the observed saturation in the conversion process as well as the shape of the STOKES pulses is due to a significant depletion of the atomic ground-state population by the pumping light. Therefore, only a small intensity of the generated infrared radiation has been observed. The spectral properties of the generated infrared light were investigated. The bandwidth of the STOKES radiation depends linearly on the width of the pump laser and is always smaller than that. Moreover it is influenced by the strontium vapour pressure and, very strongly, by the intensities of pump and generated light. (orig.)