The nonlinear optical frequency conversions of repetitively pulsed output of a 1941-nm Tm3+ : YAP laser pumped by a cw 1670-nm fibre laser are studied experimentally. Both mid-IR optical parametric oscillation (OPO) and second harmonic generation (SHG) are obtained in the same periodically poled MgO : LiNbO3 crystal with a fan-out domain design by tuning the grating period and temperature. The energy conversion efficiency of the degenerate OPO at 3820–3970 nm exceeds 43% at a 0.5 kHz repetition rate, while the energy conversion efficiency of SHG at 970.5 nm reaches 34%.
Tm3+:YAP lasers in-band fiber-laser pumped at 1670 nm with a linear or L-shaped cavity were studied in CW, actively and passively Q-switched regimes. High-efficiency CW and repetitively-pulsed operations were registered at three spectral regions: 1987–1994 nm, 1935–1941 nm and 1892–1897 nm. The transition between these three spectral regions was achieved by controlling the pump power and the output mirror in a laser cavity. The highest CW output power that was achieved without degrading the beam quality was 12.2 W at the 52% slope efficiency with respect to the incident pump. Acousto-optically Q-switched operation with the average power of 9.8 W at the 20 kHz pulse repetition rate (PRR) and 6 W at 3 kHz PRR was achieved, the pulse energy was scaled up to 2.7 mJ at 0.5 kHz PRR. The passive Q-switch operation at 1935–1938 nm was obtained using a Cr2+:ZnSe saturable absorber; the pulse energy reached 150 µJ at the 20 kHz PRR
Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize.
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