15 March 2013 Two photon absorption and stimulated Raman scattering in alkali vapor lasers
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Diode Pumped Alkali Lasers (DPAL) are being scaled to powers of greater than 1 kW and intensities exceeding 30 kW/cm2. We have demonstrated a pulsed potassium laser with pump intensities of 1 MW/cm2 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 1st and 2nd 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 2P 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 2S – 4 2D transitions are reported. The efficiency and operationally feasible of these alternative DPAL wavelengths is assessed.
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Jeffrey E. Gallagher, Edward J. Hurd, Kirk C. Brown, Glen P. Perram, "Two photon absorption and stimulated Raman scattering in alkali vapor lasers", Proc. SPIE 8604, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XII, 860403 (15 March 2013); doi: 10.1117/12.981801; https://doi.org/10.1117/12.981801

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