Mode-matching Of Diode-end-pumped Alkali Vapor Lasers

Lasers with high efficiency and high output power are one of the importanttrends due to the significant applications in fields of industry, national defence,aerospace and so on. Due to the merits of diode pumping, flowing gain medium andhigh quantum efficiency, diode-pumped alkali vapor lasers (DPALs) are potential tooutput high power with high optical to optical efficiency. Besides, the wavelengths ofDPALs locate at the atmospheric window (0.7-1.1μm) and the response band of mostphoto-conducting devices, thus DPALs can interfere these devices and have specialapplications in the military field. The output power of DPALs is as high as1kW byutilizing Cs vapor in Russia, and DPALs have also been researched deeply in China.Among the key techniques of DPALs, the technique of mode-matching between pumpmode and laser mode is very important. Better mode-matching is beneficial to reducelaser threshold and improve laser efficiency and output power. At present, themode-matching in DPALs has not been researched systemically. Therefore, we willestablish dynamics model and analyze the mode-matching characteristics, and finallydesign the experiment in this paper.Firstly, the working conditions of DPALs are analyzed, and then the keytechniques of DPALs are introduced, including line-width narrowing of pump source,collisional broadening of absorption spectrum of alkali vapor, fast mixing offine-structure levels, pump structure and cavity.Secondly, based on the rate equation theory, a theoretical model which can reflect the mode-matching performance is established by introducing the beam parameters ofpump light and oscillating light. The mode-matching efficiency ηmode, threshold pumppower Pth, and slope efficiency ηslopeare derived. Then the mode-matchingcharacteristics of an end-pumped Cs DPAL are analyzed based on the model. Theinfluences of radius ωp0and position zpof focused pump spot and alkali vapor celllength l on the mode-matching efficiency ηmode, threshold pump power Pth, and slopeefficiency ηslopeare obtained.Finally, an experiment platform of LD-end-pumped Cs DPAL is introduced.Based on this platform, the mode-matching characteristics are researched. Theexperiment parameters include radius ωp0and position zpof focused pump spot, cavitylength L and curvature radius of output coupler R. The obtained experiment resultsand conclusions can provide guidance for the optimization design of DPALs.