Coumarins in the gaseous phase. III. Coumarin 6 vapor laser with 12% efficiency

Lasing of coumarin 6 (C6) vapor mixed with diethyl ether (tauapprox.210 /sup 0/C) was observed in the range of 520 nm for transverse pumping with the third harmonic of a neodymium laser (355 nm, 20 nsec, 100 mJ). The dependence of the lasing efficiency on the transmission of the resonator mirrors was used to estimate the internal losses (0.02--0.03 cm/sup -1/) and the gain in the active medium. The amplification cross section of C6 in the 520 nm range was 3.5 x 10/sup -17/ cm/sup 2/. At the beginning of a pump pulse the lasing efficiency in the optimal resonator was 15% (and the corresponding quantum efficiency was 22%), but at the end of the pulse it fell to 10%. A study was made of the mechanisms of the induced losses. The observed fall of the efficiency was mainly due to an increase in the induced absorption and the pump wavelength. Feasibility of constructing a cw C6 vapor laser was considered.