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We report a high-power two-crystal Ho:YAG slab laser. A maximum cw output power of 146.4 W at a wavelength of 2090.7 nm is achieved, corresponding to a slope efficiency of 66.0% and an optical efficiency of 61.2%. The beam quality factor is measured to be M2 < 2.2 at different output power levels. With an acousto-optic Q-switch, a maximum average output power of 141.3, 137.7 and 134.5 W are obtained at pulse repetition rates of 20, 30 and 50 kHz, respectively. Minimum pulse widths of 39 ns, 44 ns and 74 ns are achieved for the above pulse repetition rates.

A doubly Q-switched (DQS) Ho:LuAG laser resonantly pumped by a 1.91-μm laser was first presented with an acoustic-optic modulator (AOM) and a Cr^2+:ZnS saturable absorber. A comparison among the active Q-switched (AQS), passively Q-switched (PQS), and DQS laser performances was carried out. The maximum continuous wave (CW) output power of 6 W with the central wavelength of 2100.65 nm was obtained at an incident pump power of 35.2 W. Compared with CW laser, the AQS, PQS, and DQS lasers shared the same central wavelength of 2098.34 nm under the same incident pump power. The central wavelength of the AQS and DQS lasers remained constant with the change of AOM repetition frequency (RF). When the incident pump power was 35.2 W and the AOM RF was 15 kHz, the DQS Ho:LuAG laser at a maximum RF of 2.13 kHz achieved the maximum average output power of 4.95 W. At the AOM RF of 10 kHz, the DQS Ho:LuAG laser achieved the shortest pulse width of 40.4 ns with the highest peak power of 61.5 kW. At an incident pump power of 35.2 W, the PQS Ho:LuAG laser obtained the shortest pulse width of 46.1 ns, corresponding to the RF of 2.25 kHz. Experiment results showed that the pulse width could be compressed effectively with a significant increase of peak power for a 2-μm DQS laser.

A diode pumped, injection-seeded Q-switched Er:YAG laser at 1645.2 nm is demonstrated. A single frequency Er:YAG monolithic nonplanar ring oscillator (NPRO) laser emitting at 1645.24 nm with a maximum output power of 500 mW is used as a seed laser. The seed laser output is injected into a bow-tie slave laser, obtaining stable single-frequency Q-switched operation of the Er:YAG laser. The maximum single-frequency Q-switched Er:YAG laser output energy is 2.9 mJ at 100 Hz with a pulse duration of 160 ns.

We demonstrate a continuous-wave (cw) and actively Q-switched Er : YAG ceramic laser resonantly dual-end-pumped by a 1532 nm fibre-coupled laser diode. A maximum cw output power of 1.48 W at 1645.3 nm is obtained at an absorbed pump power of 12.72 W, corresponding to a slope efficiency of 19.2%. In the Q-switched regime the maximum pulse energy of 0.84 mJ is reached at a pulse repetition rate of 100 Hz, pulse duration of 48.03 ns and absorbed pump power of 10.51 W.

We investigated the influence of counter anion on the geometry, electronic structure, and nonlinear optical (NLO) properties of (dimethylamino)stilbazolium cation (DAS+) by semiempirical quantum chemical calculation. Two different positions were considered for DAS+and the counter anion in our calculations. In the first case, the counter anion is placed at the side of the dimethylamino group of the phenyl ring of DAS+(type A). In the other case, the counter anion is placed at the side of pyridinium ring of DAS+(type B). In both the cases, for bond distances (raand rb) 1.5–50Å were considered. The geometry and electronic structure of DAS+have found to be changed due to the interaction between the counter anion and DAS+, and these changes depend on raand rb. The NLO properties of DAS+are influenced by the counter anion in a subtle way in the case of type A. The signs of first and second hyperpolarizabilities (βand γ) of DAS+are changed when the counter anion approaches DAS+, and the maximum absolute values of βand γare larger than those of DAS+without the counter anion. These results provide a guideline for molecular design of stilbazolium-based zwitterions with large NLO properties.

We report a high energy output from a Ho:YAG oscillator resonantly double-end pumped by Tm:YLF lasers at room temperature. The maximum pulse energy of 52.5 mJ was achieved at a pulse repetition rate of 100Hz and a pulse duration of 35.2 ns, corresponding to a peak power of approximately 1.5 MW. The output wavelength was 2090.7 nm with beam quality factor M2 [?] 1.2.

The performance of a Tm : YLF slab laser is studied at different output coupler parameters. Use is made of a 20-mm-long a-cut slab crystal doped with 2.5 at. % thulium ions. With a volume Bragg grating and a Fabry - Perot etalon, the selected output wavelength of this Tm : YLF slab laser is 1908 nm. For the optimised output coupler with a transmission of 20% and a radius of curvature of 300 mm, the output power exceeds 74.1 W and the slope efficiency with respect to the absorbed pump power reaches 48.4%. In addition, the beam quality of the Tm : YLF slab laser is improved.

Spectroscopic characterization of a Ho:LuVO_4 crystal grown by the Czochralski method has been performed, including the absorption and emission spectra. We demonstrate a 2 μm room temperature Ho:LuVO_4 laser, resonantly pumped by a 1.94 μm Tm:YAP laser. By use of an output coupler with T=10% transmission, the Ho:LuVO_4 laser generated continuous-wave output power of 2.5 W at 2074.18 nm, with a beam quality factor of Mx2=My2=1.3, for a total incident pump power of 19.4 W. The slope efficiency with respect to the pump power was 17.6%, and the optical-to-optical efficiency was 12.9%. Moreover, we obtained a Ho:LuVO_4 laser that operated at 2073.77 and 2055.27 nm, by using different output couplers with transmissions of T=15 and 30%.

An efficient 2 μm room-temperature Q-switched Ho:GdVO_4 laser end-pumped by a 1942 nm Tm-fiber laser is demonstrated. To our knowledge, this is the first report of Q-switched performance of Ho:GdVO_4 crystal. A maximum CW output power of 6.85 W under the absorbed pump power of 24.1 W was obtained with a slope efficiency of 39.5% at a temperature of 17°C. With the same absorbed pump power, a maximum output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at the pulsed repetition frequency (PRF) of 5 kHz, corresponding to a peak power of approximately 187.2 kW.

Single-frequency operation in the range of 2102.45–2102.54?nm and 2130.72–2130.82?nm is demonstrated from a Tm,Ho:YAP laser at room temperature. To our knowledge, this is the first time a room temperature single-frequency Tm,Ho:YAP laser of up to 72.6?mW at 2102.5?nm with Fabry-Perot etalons has been obtained. Regulating the elevation angle of the two etalons, 42.0?mW at 2130.8?nm was obtained. The single-longitudinal-mode laser can be used as a seed laser for coherent wind measurements and differential absorption lidar systems.

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