Two photon absorption and Stimulated Raman Scattering in alkali vapor lasers

Diode Pumped Alkali Lasers (DPAL) are being scaled to powers of greater than 1 kW and intensities exceeding 30 kW/cm 2 . We have demonstrated a pulsed potassium laser with pump intensities of 1 MW/cm 2 and efficiency exceeding 10%. At these higher pump intensities, nonlinear processes including two photon absorption and Stimulated Raman Scattering offer alternative wavelengths for these gas lasers. We have observed 1 st and 2 nd order Stokes and anti-Stokes lasing due to Stimulated Electronic Raman Scattering (SERS) in a potassium cell. When the pump is tuned about halfway between the fine structure levels of the 4 2 P state, an efficient hyper-Raman process dominates. Up to 12 mW of red light is produced at a pump input of 232 mW. The threshold for the hyper-Raman process is about 60 mW. This type of laser may be useful for beam propagation experiments where a tunable probe beam spectrally close to the main beam is desired. Two-photon absorption at wavelengths near then DPAL pump transition has also been observed and used to demonstrate lasing in the blue and mid infrared. The transmission of a scanning cw ring laser through a static Rb cell reveals two-photon absorbance of greater than 10%. An absolute determination of the two-photon absorption crosssections for the Rb 5 2 S – 4 2 D transitions are reported. The efficiency and operationally feasible of these alternative DPAL wavelengths is assessed.