T.M. Huang

Optimization in scaling fiber-coupled laser-diode end-pumped lasers to higher power: influence of thermal effect

The optimum mode-to-pump ratio in scaling fiber-coupled laser-diode end-pumped lasers to higher power has been investigated by including the thermal effect into the space-dependent rate equation analysis. The optical path difference (OPD) distribution has been derived as a function of the pump-beam quality, focus position of pumping light, and pump radius at the focal plane under the assumption that the end faces of the crystal are thermally insulated. The diffraction losses arising from thermally induced spherical aberration have been estimated by the Strehl intensity ratio. The present results for the optimum mode-to-pump ratio are markedly different from previous analyses in which thermal effects are neglected. Here, the optimum mode-to-pump ratio is a decreasing function of input pump power, and is less than unity in the case of a slightly high pump power. The practical example of a Nd:YAG laser pumped by a 13-W fiber-coupled laser diode is considered to confirm our physical analysis.

Generation of Hermite-Gaussian modes in fiber-coupled laser-diode end-pumped lasers

Abstract.A technique has been developed for the generation of Laguerre–Gaussian (LG0,l) modes in a fiber-coupled laser diode end-pumped microchip laser. A theoretical model is also developed to predict how the oscillation of LG0,l modes is affected by the pump position, the pump size and the cavity mode size. With a 1-W fiber-coupled diode, the highest-order LG0,l mode that can be generated is l=23.

Optimization of fiber-coupled laser-diode end-pumped lasers: influence of pump-beam quality

A general model has been developed for the optimization of fiber-coupled laser-diode pumped lasers by including the effect of pump-beam quality into the mode-overlap integrals. The numerical results of the mode-overlap integrals have been fitted to an analytical function of pump spot size, laser mode size and the parameter /spl beta/, which is in terms of laser-diode beam quality and properties of the active medium. This analytical function allowed us to obtain explicit formulae for the threshold pump power, the slope efficiency, and the optimum pump spot size. With these formulae, the optimum mode size and the maximum output efficiency can be easily calculated for arbitrary values of /spl beta/ and input power. From the numerical results, we obtained an analytical expression to relate the required input power and pump-beam quality to the desired output efficiency and properties of an active medium. The present model provides a straightforward procedure to design the laser resonator and the optical coupling system for optimization. To illustrate the utility of the present model, a Nd:YAG laser pumped by fiber-coupled laser diodes is considered and optimized.

Study of high-power diode-end-pumped Nd:YVO4 laser at 1.34 μm: influence of Auger upconversion

Abstract We demonstrated an experimental study of the influence of the Nd 3+ concentration on scaling diode-pumped Nd:YVO 4 1.34-μm lasers to higher power. An output power of 5.1 W at 1.34 μm was obtained with a 0.5-at.% Nd-doped YVO 4 at 13.5 W of incident pump power. The strong dependence of the slope efficiency on the dopant concentration is attributed to an Auger upconversion process.

Efficient high-power diode-end-pumped TEM/sub 00/ Nd:YVO 4 laser

We demonstrate a compact and efficient diode-end-pumped TEM/sub 00/ laser with output power of 25.2 W for 52 W of incident pump power by use of a single YVO/sub 4/ crystal with a Nd concentration of 0.3 at.%. In Q-switched operation 21-W of average power at a pulse repetition rate of 100 kHz and /spl sim/1.1-mT pulse energy at a pulse repetition rate of 10 kHz were produced. At 10 kHz, the pulse width is around 10 ns and the peak power is higher than 100 kW.

Influence of thermal effect on output power optimization in fiber-coupled laser-diode end-pumped lasers

A general model has been developed for the output power optimization of fiber-coupled laser-diode end-pumped lasers by including the thermal effect into the analysis. The optical path difference (OPD). Distribution has been derived as a function of the pump-beam quality, focus position of pumping light, and pump radius at the focal plane under the assumption that the end faces of the crystal are thermally insulated. With the derived OPD, the diffraction losses arising from thermal-induced spherical aberration have been estimated by the Strehl intensity ratio. The practical example of an Nd:YVO/sub 4/ laser pumped by a 1.2-W fiber-coupled laser diode is considered to illustrate the utility of the present model. Experimental results have shown a fairly good agreement with the theoretical predictions.

Single-mode oscillation of compact fiber-coupled laser-diode-pumped Nd:YVO/sub 4//KTP green laser

A compact efficient single-longitudinal-mode green laser has been demonstrated in a simple resonator formed by a coated Nd:YVO/sub 4/ crystal and a coated KTP crystal. The thermal-induced lens in the crystal provides a stable resonator with a good overlap of laser mode and pump size due to the circular pump profile of the fiber-coupled diode. Under the optimum cavity-length condition, 206 mW of green output power corresponding to a conversion efficiency 26.8% was obtained when pumped by a 770 mW fiber-coupled laser diode.

Investigation of fiber-coupled laser-diode-pumped NYAB green laser performance

The optimum pump condition for a fiber-coupled diode end-pumped Nd:YAl/sub 3/(BO/sub 3/)/sub 4/ laser has been determined by including the effect of pump beam quality into the analysis. Under the optimum pump condition, 67 mW of the green laser output corresponding to a conversion efficiency 10.3% was obtained from a self frequency-doubling NYAB crystal when pumped by a 650 mW fiber-coupled laser diode. The prospect of higher conversion efficiency is also discussed.

Theoretical and experimental studies of single-mode operation in diode pumped Nd:YVO4/KTP green laser: influence of KTP length

Abstract We present a theoretical study of the single-mode operation in a diode pumped Nd:YVO4/KTP green laser by considering the combined action of the anisotropic emission cross-section of Nd:YVO4 and the KTP crystal acting as a birefringent filter. The influence of the KTP length on the performance of single-mode operation was investigated. Comparison between theoretical predictions and experimental results is presented.

Analysis of the effect of pump position on transverse modes in fiber-coupled laser-diode end pumped lasers

Abstract We have derived a formula to study the effect of pump position on transverse modes of end-pumped solid-state lasers. From this formula an analytical expression relating the threshold power of the single TEM n ,0 -mode oscillation to the pump position can be obtained with suitable average pump size. The permissible limit to obtain single-transverse-mode operation can be also determined. Experimental results have shown a fairly good agreement with the theoretical predictions.