Nonlinear Optical Crystals: A Complete Survey

https://hal.archives-ouvertes.fr/hal-00140068/document

On thermal effects in solid state lasers: the case of ytterbium-doped materials

First‐principles electronic structure calculations on wurtzite AlN, GaN, and InN reveal crystal‐field splitting parameters ΔCF of −217, 42, and 41 meV, respectively, and spin–orbit splitting parameters Δ0 of 19, 13, and 1 meV, respectively. In the zinc blende structure ΔCF≡0 and Δ0 are 19, 15, and 6 meV, respectively. The unstrained AlN/GaN, GaN/InN, and AlN/InN valence band offsets for the wurtzite (zinc blende) materials are 0.81 (0.84), 0.48 (0.26), and 1.25 (1.04) eV, respectively. The trends in these spectroscopic quantities are discussed and recent experimental findings are analyzed in light of these predictions.

Valence band splittings and band offsets of AlN, GaN and InN.

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.

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

The mechanisms of size-dependent efficiency and efficiency droop of blue InGaN micro-pixel light emitting diodes (μLEDs) have been investigated experimentally and by simulation. Electrical characterisation confirms the improvement of current spreading for smaller μLEDs, which enables the achievement of the higher efficiency at high injection current densities. Owing to the higher ratio of sidewall perimeter to mesa area of smaller μLEDs, a lower efficiency was observed at a low injection current density, resulting from defect-related Shockley-Read-Hall non-radiative recombination. We demonstrate that such sidewall etch defects can be partially recovered by increased thermal annealing time, consequently improving the efficiency at low current densities.

Size-dependent efficiency and efficiency droop of blue InGaN micro-light emitting diodes

We demonstrate a high-power passively Q -switched and mode-locked Nd:YVO(4) laser with a Cr(4+):YAG saturable absorber. 2.7 W of average power with an 18-kHz Q -switched repetition rate was generated at a 12.5-W pump power. The peak power of a single pulse near the maximum of the Q -switched envelope was greater than 100 kW.

https://ir.nctu.edu.tw:443/bitstream/11536/30222/1/000089438400012.pdf

High-power diode-pumped Q-switched and mode-locked Nd:YVO(4) laser with a Cr(4+):YAG saturable absorber.

We report efficient generation of cw yellow light by use of single-pass sum-frequency mixing from a diode-pumped Nd:YVO4 dual-wavelength laser with periodically poled lithium niobate. A diode-pumped Nd:YVO4 dual-wavelength laser is implemented with a three-mirror cavity, and the optimum oscillation condition is obtained from theoretical analysis. We extracted 78 mW of power at 593 nm from 1.2 W at 1064 nm and from 1.0 W at 1342 nm in a beam with excellent quality. The output power could probably be increased to ∼92 mW by antireflection coating of the crystal.

Efficient generation of continuous-wave yellow light by single-pass sum-frequency mixing of a diode-pumped Nd : YVO4 dual-wavelength laser with periodically poled lithium niobate

A general model has been developed for the generation of Hermite-Gaussian modes in fiber-coupled laser-diode end-pumped lasers by off-axis pumping. Hermite-Gaussian modes can be used as an M/sup 2/ standard in the calibration process due to the fact that these modes have a definite M/sup 2/ factor. The present model predicts how the oscillation of Hermite-Gaussian modes is affected by the pump position, the pump size, and cavity mode size. A straightforward procedure have also been provided to design the optical coupling system for the lowest threshold in the generation of Hermite-Gaussian modes. All of the key parameters of the optimum pump condition are in terms of laser-diode beam quality and properties of the active medium. Experimental results have shown a fairly good agreement with the theoretical predictions.

/pdf/generation-of-hermite-gaussian-modes-in-fiber-coupled-laser-1ackhcs24c.pdf

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

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.

S. C. Wang

Papers

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

High-power diode-pumped Q-switched and mode-locked Nd:YVO(4) laser with a Cr(4+):YAG saturable absorber.

Efficient generation of continuous-wave yellow light by single-pass sum-frequency mixing of a diode-pumped Nd : YVO4 dual-wavelength laser with periodically poled lithium niobate

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

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