Control of the thermal lensing effect with different pump light distributions

Reconstruction method of axisymmetric refractive index fields with background-oriented schlieren

A refractive index field can be quantitatively visualized by using a background-oriented schlieren (BOS) technique to measure the displacements of background dot patterns of a 2D image captured by a camera. In BOS, the displacement is caused by the deflection of the light ray passing through the refractive index field. However, obtaining depth information of refractive index fields is often difficult because dot-pattern displacement results from deflection of light rays integrated over their path. A method of reconstructing depth information of the refractive index field using an inverse matrix method with the BOS technique is proposed here under the assumption of an axisymmetric refractive index field. A field, generated by laser irradiation inside a glass, is reconstructed by the proposed method and is also theoretically calculated using the heat diffusion equation and thermal stress theory. The reconstructed field agrees well with the theoretically calculated one, which validates the proposed method. The proposed method is a promising candidate for measuring axisymmetric refractive index fields of various media.

Exploiting concave-convex linear resonators to design end-pumped solid-state lasers with flexible cavity lengths: Application for exploring the self-mode-locked operation

The characteristics of a convex-concave linear resonator under the thermal lensing effect are theoretically analyzed to find an analytical model for designing end-pumped solid-state lasers with flexible cavity lengths. By exploiting the design model, the power scaling for continuous-wave operation under strong thermal lensing can be easily achieved in the proposed resonator with different cavity lengths. Furthermore, the proposed resonator is applied to explore the exclusive influence of cavity length on the self-mode-locked (SML) operation. It is discovered that the lasing longitudinal modes will split into multiple groups in optical spectrum to lead to a multi-pulse mode-locked temporal state when the cavity length increases. Finally, a theoretical model is derived to reconstruct the experimental results of SML operation to deduce a simple relationship between the group number of lasing modes and the cavity length.

Analytical solutions for anisotropic time-dependent heat equations with Robin boundary condition for cubic-shaped solid-state laser crystals

The problem of finding analytical solutions for time-dependent or time-independent heat equations, especially for solid-state laser media, has required a lot of work in the field of thermal effects. However, to calculate the temperature distributions analytically, researchers often have to make some approximations or employ complex methods. In this work, we present full analytical solutions for anisotropic time-dependent heat equations in the Cartesian coordinates with various source terms corresponding to various pumping schemes. Moreover, the most general boundary condition of Robin (or impedance boundary condition), corresponding to the convection cooling mechanism, was applied. This general condition can be easily switched to constant temperature and thermal insulation as special cases. To this end, we first proposed a general approach to solving time-dependent heat equations with an arbitrary heat source. We then applied our approach to explore the temperature distribution for three cases: steady-state pumping or long transient, single-shot pumping or short transient, and repetitively pulsed pumping. Our results show the possibility of an easier and more accurate approach to analytical calculations of the thermal dispersion, thermal stresses (strains), thermal bending, thermal phase shift, and other thermal effects.

36-W diode-pumped continuous-wave 1319-nm Nd:YAG ceramic laser

Continuous-wave output at 1319 nm was obtained from a laser-diode-pumped 1% ceramic Nd:YAG laser. As much as 36.3-W output was obtained under pump power of 290 W, with an optical-to-optical conversion efficiency of 12.5%.

Passively Q-Switched Diode-Pumped Continuous-Wave Nd:YAG-Cr(4+):YAG Laser with High Peak Power and High Pulse Energy

A high peak power and high pulse energy passively Q-switched diode-pumped cw Nd:YAG laser at 1.064-mum wavelength has been demonstrated with Cr(4+):YAG crystal as the saturable absorber. The average output power of 7-12 W and pulse duration of 100-250 ns was obtained with kilohertz repetition rates. The highest peak power and pulse energy obtained were 30 kW and 3.4 mJ, respectively. All the output resulted from the TEM(00) mode with M(2) < 1.1. The thermal lensing effect of the saturable absorber was investigated, demonstrating that it played an important role in optimization of the output.

Simultaneous multiple-wavelength cw lasing in laser-diode-pumped composite rods of Nd:YAG and Nd:YLF

Simultaneous multiple-wavelength cw laser operations were achieved in two types of composite laser rod composed of Nd(3+):YAG and Nd(3+):YLF crystals, which were laser diode (LD) pumped within a single virtual-point-source cavity. As much as 30 W of total output at 1064- and 1047-nm wavelengths was obtained under 150-W LD input power, with approximately 25% from the 1047-nm wavelength. Different bonding methods were compared, showing that the use of an optical adhesive is effective and presents no deterioration at low and middle power levels. Simultaneous multiple-wavelength operation at 1064- and 1053-nm wavelengths was also studied.