Eduard Wyss

Generation of radially polarized beams in a Nd: YAG laser with self-adaptive overcompensation of the thermal lens

Thermal effects such as lensing and birefringence negatively affect the beam quality and limit the power range of solid-state lasers. Self-adaptive overcompensation of the thermal lens is an answer to this problem. It provides a laser system with good beam quality and large stability range. Because the focal length of the thermally induced lens is different for the radial and the tangential polarization, overcompensation can be used to discriminate these two polarizations. Exploiting this method, we demonstrate the generation of radially polarized beams in a self-adaptively overcompensated high-power Nd:YAG laser with an output power of 155 W and an M2 of less than 10.

Thermooptical compensation methods for high-power lasers

Thermally induced optical effects can be exploited to generate adaptive optical devices such as self-adjusting lenses. An adaptive lens in a resonator can be used to compensate for the thermal lens in a high-power solid-state laser rod (LR) and herewith significantly improve the beam quality and increase the output-power range of solid-state lasers. With suitable materials and an appropriate design of the compensating device, resonators with self-balancing thermal lenses can be developed. In this paper, we review the material requirements for a self-adaptive compensating element and discuss a selection of suitable materials (glasses, liquids and curing gels) and schemes to compensate for the thermal lens of a Nd:YAG LR. Finally, we present a very simple and promising design of a thermooptically self-compensated laser amplifier.

Laser microhole drilling using Q-switched radially and tangentially polarized beams

Laser microhole drilling using radially and tangentially polarized Q-switched laser radiation has been analyzed comparatively. Tangential polarization exhibited a significantly higher drilling speed compared to radial polarization. Light attenuation through interaction with the walls of a microhole was found to be weaker in the case of tangential polarization than in the case of radial polarization, thus leading to the assumption that the observed higher drilling rates utilizing tangential polarization are due to more energy being deposited at the bottom of a microhole. The required radiation has been generated using a Q-switched Nd:YAG laser resonator in a configuration that exploits thermally induced birefringence to render the laser resonator stable only for radial polarization.

End-pumped Nd:YAG laser with self-adaptive compensation of the thermal lens

Thermally induced lenses are the most critical problem in the development of high-power solid-state lasers. To compensate for thermal lenses, we have been investigating self-adaptive compensation methods based on thermal effects themselves. Recently, we demonstrated a novel compensation scheme for transversally pumped lasers. This scheme has now been adapted to an end-pumped laser system. The reduction of the thermal lens has been simulated and measured experimentally. The experiments were carried out with a diode-pumped Nd:YAG laser with a maximum output power of 15.6 W.

Self-Adaptive Compensation for the Thermal Lens in High-Power Lasers

An adaptive negative thermal lens that compensates for the power-dependent positive thermal lens in a transversally diode-pumped Nd:YAG laser rod is presented. We demonstrate that the proposed technique leads to a reduction of the total thermal lens in the resonator by more than an order of magnitude.

Solid-state lasers at the stability limit: constant beam properties over large power ranges

Without adaptive optics high-power lasers suffer either from poor beam quality or limited power ranges. A laser can be forced to operate on its stability limit by self-adaptive overcompensation resulting in constant and good beam quality over a large power range. With this technique, the brightness of a Nd:YAG laser was increased by almost an order of magnitude despite highly aberrated thermal lens in the laser rod.

Adaptive thermal optics in high-power laser resonators

In order to compensate for the thermally induced lenses in high-power laser rods we investigate self-adaptive techniques based on thermo-optical processes. Recently we have demonstrated that the influence of the thermal lense in high-power lasers can be reduced significantly by means of a thin liquid layer located within the resonator. Here we report on the investigations of different liquids and gels for the generation of the adaptive lens and discus an improved implementation of the technique, with the compensating layer placed directly in contact with the laser rod.

Generation of radial polarization in Nd:YAG and CO2 lasers and its applications

Radially polarized radiation shows some very interesting properties and has therefore gained interest in recent years. An overview of the advantages and the various applications where radially polarized modes are beneficial is given. In addition the different known methods to generate radial polarization are reviewed. In our work we developed a method to generate radially polarized laser beams by means of a polarization selective resonant grating mirror. The undesired polarization is coupled to a mode of the dielectric multilayer of the resonator end mirror and experiences severe losses while the radial polarization is not affected and oscillates in the laser resonator. Fundamental and higher-order radially polarized modes of high polarization purity and powers of more than 100W have been demonstrated.

Thermo-optical self-compensated amplifiers for high-power laser resonators

Thermally induced optical effects can be exploited to generate adaptive optical devices such as self adjusting lenses. A liquid or gel layer sandwiched between two laser rods can self-adaptively compensate for the thermal lenses in the laser rods and therefore significantly increase the power range and the output beam quality of high-power lasers. Thermo-optically self-compensating amplifiers and their influence on optical resonators are discussed.

Exploiting thermal effects in high-power lasers

An adaptive negative thermal lens that compensates for the power-dependent positive thermal lens in a transversally diodepumped Nd:YAG laser rod is presented. We demonstrate that the proposed technique leads to a reduction of the total thermal lens by more than an order of magnitude. In addition we propose a novel method to obtain a linearly polarised output beam from a Nd:YAG laser without a compensation for the thermally induced birefringence.