A Tm:YAP slab laser with double-end-pumped and high efficiency under room temperature is introduced. Considering the cooling of the end faces and lateral faces of the crystal, analyses of the thermal effects in which all six faces cooled by the convection cooling mechanism was assumed to solve the equations of heat conduction. By using the double-concave geometry to offset thermal lens effect, the maximum output power was 25.02W at the incident pump power of 75.97W, corresponding to the optical-to-optical efficiency of 37.05% and slope efficiency of 35.85%. F-P etalon is inserted in the cavity to control laser FWHM line width of 0.44nm at 1938.7nm. And the optical beam quality is measured when pumped power is 20W,which is the beam quality factor of M2 was estimated of 3.25 in x-direction and 2.79 in y-direction.
Due to 2 μm band in the absorption of water and CO2, the diode pumped solid state lasers with wavelength around 2 μm have important applications in laser medicine and remote sensing, such as it can be used as a scalpe or a light source of Coherent Doppler Wind Lidar and Differential Absorption Lidar. In the recently years, scientists have done much work on the development of such lasers. There’re many reports on continuous Tm:YAG laser. However, the study on Q-switched Tm:YAG laser, which is more useful in applications, was very rare. As the light source of Coherent Doppler Wind Lidar, large energy and wide pulse width is desired. Current reports mostly adopted CW pumped source, but it would make a mount of heat. Pulse pumping method could reduce the heat accumulation and improve the heat stability of the laser. How to improve the single pulse energy was the focus of current study. In this paper, a single end bonding Tm:YAG crystal with Tm3+ doping concentration of 3.5at.% was used. Acousto-optic (AO) Q-switched (GOOCH and HOUSEGO QS041-10M-HI8) operation was adopted in our experiment. In the repetition frequency of 100Hz, a maximum single energy of 2.67 mJ (measured by Ophir 30A-BB) and the narrowest pulse width of 149 ns (measured by Vigo PCI-3TE-12 detector) were achieved at room temperature. The M2x was 1.31 and the M2y was 1.35 (measured by Spiricon Pyrocam-III). Tm:YAG laser was developed by using a pulse diode pumped L shape resonant cavity. The transmittance of the curve output mirror was 4% and the curvature radius of which was 300 mm. The output center wavelength of the laser was measured to be 2013.5 nm (measured by YOKOGAWA AQ6375).
The theoretical model of thermal-steady-state anisotropic Tm:YLF crystal was built based on the practical operation
condition. Integral transformation was used to get the analytical expression of the distribution of temperature in Tm
crystal and thermal focal length. Matlab was used to simulate the influence of pump power density, crystal length and
doping density to the distribution of temperature and thermal focal length. The results showed that under the invariant
pumping power density and crystal length, the temperature rise and nonuniformity of thermal distortion are intensified by
the increase of doping density which leads to a worse thermal effect. Under the invariant pumping power and doping
density, the temperature rise and nonuniformity of thermal distortion are weaken by the modest increase of crystal length
which leads to a good thermal condition. When the product of crystal length and doping concentration is a constant value,
the thermal focal length keeps basic consistent. Furthermore, the simulated results are that when the dual-pumped power
is 60W and waist radius is 430μm, the thermal focal length of 12mm, 3at.% doped which perpendicular and parallel to c
axis are 184mm and 261mm respectively, and the thermal focal length of 12mm, 3.5at.% doped which perpendicular and
parallel to c axis are 171mm and 243mm respectively. The results in this paper provide theoretical basis for thermal
compensation and cavity design of dual-pumped Tm:YLF laser, meanwhile, the model built can be used to analyze other
anisotropic crystals.
A mid-infrared optical parametric oscillator (OPO) with an idler wavelength of 3.85 μm at a repetition rate of 200 kHz is presented, and a high-repetition-rate electro-optic (EO) Q-switched Nd∶GdVO 4 laser with a double-crystal RbTiOPO 4 EO modulator is used as the pump source. The OPO is designed as an extracavity singly resonant optical parametric oscillator. The threshold value of the OPO system is only 1.3 W at 1.06 μm. When the MgO: periodically poled lithium niobate (MgO: PPLN) crystal is operated at 90°C and the pump power is 10.5 W with a repetition of 200 kHz, a maximum average output power of 1.82 W at idler wavelength of 3.85 μm and pulse width of 14.3 ns are obtained. The slope efficiency of the 3.85-μm laser with respect to the pump laser is 21.3%. The M 2 factors of the 3.85-μm laser are 1.84 and 1.76 in the parallel and perpendicular directions, respectively. The mid-infrared tunability of 3.7 to 3.9 μm can be achieved by adjusting the temperature of MgO∶PPLN crystal from 210 to 35°C.
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