Xiaojin Cheng

Structure and Heat Capacity of Wurtzite GaN from 113 to 1073 K

High pure wurtzite structure GaN has been synthesized by gas reaction method. Its structure was determined by powder x-ray diffraction using the Rietveld technique. The heat capacity C-p was measured from 113 to 1073 K, which can be represented by C-p = 0.362 + 3.010 x 10(-4)T - 3.411 x 10(3)T(-2) - 7.791 x 10(-8)T(2). NO measurable phase transition was observed in this temperature range.

Efficient Q-switched Tm:YAG ceramic slab laser

Characteristics of Tm:YAG ceramic for high efficient 2-μm lasers are analyzed. Efficient diode end-pumped continuous-wave and Q-switched Tm:YAG ceramic lasers are demonstrated. At the absorbed pump power of 53.2W, the maximum continuous wave (cw) output power of 17.2 W around 2016 nm was obtained with the output transmission of 5%. The optical conversion efficiency is 32.3%, corresponding to a slope efficiency of 36.5%. For Q-switched operation, the shortest width of 69 ns was achieved with the pulse repetition frequency of 500 Hz and single pulse energy of 20.4 mJ, which indicates excellent energy storage capability of the Tm:YAG ceramic.

High-power diode-end-pumped Tm:LiLuF4 slab lasers

Diode-end-pumped continuous-wave and acousto-optics Q-switched Tm:LiLuF(4) slab lasers were demonstrated. The a-cut Tm:LiLuF(4) slab with doping concentrations of 2 at.% was pumped by fast-axis collimated laser diodes at room temperature. The maximum continuous-wave output power of 10.4 W was obtained while the absorbed pump power was 31.6 W and the cavity length was 30 mm. For Q-switched operation, we got the maximum pulse energy of 8 mJ with pulse width of 315.2 ns at 1 KHz pulse repetition frequency.

High-power diode-end-pumped Tm:YAP and Tm:YLF slab lasers

Diode-end-pumped continuous-wave (CW) Tm:YAP and Tm:YLF slab lasers are demonstrated. The a-cut Tm:YAP and Tm:YLF slabs with doping concentrations of 4 at.-% and 3.5 at.-%, respectively, are pumped by fast-axis collimated laser diodes at room temperature. The maximum CW output powers of 72 and 50.2 W are obtained from Tm:YAP and Tm:YLF, respectively, while the pump power is 220 W, corresponding to the slope e±ciencies of 37.9% and 26.6%, respectively.

Short Tm3+-doped fiber lasers with watt-level output near 2 microns

High-power operation of diode-pumped fiber lasers at wavelength near 2 microns are demonstrated with short length of heavily Tm3+-doped silica glass fibers. With 7-cm long fiber, a laser at near 2 microns is obtained with the threshold of 135 mW, maximum output power of 1.09 W, and slope efficiency of 9.6% with respect to the launched power from a laser diode at 790 nm. The output stability of this fiber laser is within 5%. The dependence of the performance of fiber lasers on the operation temperature and cavity configuration parameters is also investigated.

Generation of 6.05J nanosecond pulses at a 1Hz repetition rate from a cryogenic cooled diode-pumped Yb:YAG MOPA system

Diode-pumped solid state laser system based on cryogenic Yb:YAG active-mirror scheme are presented with recent energy output. With improved optical design, 6.05J/1Hz pulse energy is achieved and a conceptual design with 30J output energy is theoretical simulated. The doubling efficiency of YCa4O (BO3)(YCOB) crystal is also discussed in this paper.

Study of diode-pumped Yb:YAG disk lasers at low temperature

A Yb:YAG disk laser with V-shaped stable resonator and active-mirror configuration, end-pumped by a 940-nm InGaAs laser diode array, is demonstrated. Performances and optimization of the disk laser at low temperature over a range of 130-200 K are investigated theoretically and experimentally. Laser output energy of 1.46 J/pulse operating at 10-Hz repetition rate is obtained with the optimum output coupler transmission of 30%, and the corresponding optical-to-optical efficiency is 48.7%.

Diode-end-pumped Tm 3+ -doped thin slab solid-state lasers

We report diode-end-pumped continuous-wave Tm:YAlO3 crystal and Tm:YAG ceramic thin slab lasers. At room temperature, when pumped by fast-axis collimated laser diodes, the maximum output powers of Tm:YAlO3 crystal and Tm:YAG ceramic are 15 W and 4.5W respectively.