We examined the performance of potassium diode pumped alkali laser (K DPAL) using He, Ar, Methane (CH4), Ethane (C2H6) and a mixture of He and CH4 as a buffer gas to provide spin-orbit mixing of the 4P3/2 and 4P1/2 states of Potassium atoms. We found that pure helium as an efficient buffer gas for K DPAL with a static gain medium can be used only for pulsed operation with up to 50 µs pulse durations. The performance degradation of K DPAL with pure helium for longer pulses can be explained by ionization, which causes an effective reduction in neutral alkali atoms number density. Using a flowing system for the K DPAL allows improving its operation in continuous wave (CW) mode, but for efficient lasing with pure He buffer gas, a considerable flow speed of about 100 m/s is required. In contrast, using a small amount of methane or ethane (10-20 Torr) mixed with helium at total pressure of about 1 atm, an efficient continuous wave lasing can be achieved with very moderate flow speeds of about 1 m/s. Argon buffer gas was also tested in this experiments, but it did not support lasing neither in pulsed nor in CW mode of K DPAL operation.

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Boris V. Zhdanov, Matthew D. Rotondaro, Michael K. Shaffer, and Randall J. Knize, "Potassium diode pumped alkali laser performance study using He, Ar, CH4 and C2H6 as buffer gas (Conference Presentation)," Proc. SPIE 10637, Laser Technology for Defense and Security XIV, 1063710 (Presented at SPIE Defense + Security: April 19, 2018; Published: 14 May 2018); https://doi.org/10.1117/12.2309787.5783267420001.