Multi-photon processes in alkali metal vapors

摘要

Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n ~2D_(5/2), n ~2D_(3/2) or higher energy levels, then the blue fluorescence of (n+1) ~2P_(3/2),(n+l) ~2P_(1-2)→n ~2S_(1/2) are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.