A repetition-frequency-controllable double Q-switched (DQS) Ho:LuAG laser at 2098.34 nm with acousto-optic modulator (AOM) and Cr2+:ZnS saturable absorber (SA) was investigated. The maximum output power of 5.3 W was obtained at the AOM repetition frequency (RF) of 3.72 kHz, corresponding to the slope efficiency of 29.8%. The largest pulse energy of 2.8 mJ with the shortest pulse width of 54.2 ns was observed at the AOM RF of 2.64 kHz. Compared with the passively Q-switched Ho:LuAG laser, the DQS Ho:LuAG laser could generate shorter pulse width and larger pulse energy, and its RF could be controlled by the AOM RF.
We present the optical and spectroscopic characterization and the first example of laser operation of Yb doped LuYAG ceramics, with two different compositions, namely (Lu0.25Y0.75)3Al5O12 and (Lu0.50Y0.50)3Al5O12, both with 15% Yb doping. Ceramic samples were prepared by reactive sintering from high purity α-Al2O3, Lu2O3, Y2O3, Yb2O3 powders using Tetraethoxysilane (TEOS) and MgO as sintering aids. After ball milling, the slurry was dried, uniaxially pressed into 20 mm diameter pellets at 20 MPa, and then cold isostatically pressed at 200 MPa. Sintering was conducted at 1850°C for 30 h under vacuum, followed by annealing in air (1500 °C, 10 h) to remove the oxygen vacancies. Laser tests were carried out in a laser cavity end pumped by a fiber coupled diode laser emitting at 936 nm. A slope efficiency as high as 65.2% with a maximum output power of 8.7 W (in quasi-CW pumping conditions) was obtained from the sample with composition (Lu0.25Y0.75)3Al5O12, whereas the sample with composition (Lu0.50Y0.50)3Al5O12 had a maximum slope efficiency of 49.5% (due to the higher scattering losses), and 6.7 W of maximum output power. Furthermore we characterized the tuning range of the two samples.
In order to mitigate the dopant concentration gradient by post-growth diffusion method, high optical quality Cr2+:ZnSe ceramics had been prepared by hot-pressing method with powders being diffusion doped in a previous step, which reduced the concentration gradient down to a grain size level. A optimal combination of sintering parameters, including
temperature, pressure, dwell time, have been determined (1050°C/150MPa/2h) according to background absorption
intensity. Comparison with diffusion doped CVD-grown ZnSe showed a stronger background absorption and blueshifted
emission peak, both indicating scattering sources inside material. Micro-structure observation proved the
inference above as being residual pores and inclusions, which could be eliminated or reduced by, as suggested here,
preliminary treatment of powders and enhancement of densification pressure and dwell time.
The relationship between optical scattering losses and microstructure, especially inside pores distribution, was studied in
transparent Nd:YAG and Yb:YAG ceramics. Specimens with different transmittance values were fabricated by vacuum
sintering from 1730°C to 1760°C for 30 to 50 h through a solid-state reaction method. Light scattering losses were
calculated from transmittance values measured by UV-Vis-IR spectrophotometer. Micromechanism, including inside
pores and grains on etched surfaces, was characterized via high magnification optical microscope. The porosities were
also counted in microscope observation. Curves of the relations between scattering losses (or transmittances) and
porosities were obtained. In addition, the genesis of inside pores and the process of exhaust were discussed in this paper.
Composite YAG/2.0at%Nd:YAG transparent ceramic was fabricated by solid-state reactive sintering a mixture of
commercial α-Al2O3, Y2O3, and Nd2O3 powders with tetraethoxysilane (TEOS) and MgO as sintering additives. A fully
dense YAG/2.0at%Nd:YAG ceramic with an average grain size of ~20μm was obtained by vacuum sintering at 1750°C
for 50h. There are almost no pores or second phases present at grain boundaries or inner grains. The in-line transmittance
reached 83.6% at the lasing wavelength of 1064nm and 82.0% at 400nm. The porosity of the sample was at the level of
several vol ppm. The composite YAG/2.0at%Nd:YAG transparent ceramics are promising to generate high-energy laser.
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