Michelle S. Roth

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.

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-compensating amplifier design for cw and Q-switched high-power Nd:YAG lasers.

We experimentally demonstrate a self-adaptive compensation of the pump power dependent thermal lens in an Nd:YAG laser through a thin layer of a medium with a negative temperature dependence of the refractive index. The layer is thermally coupled to the laser rod and leads to a strikingly improved beam quality over a large stability range. The scheme allows for a scaling to high powers as well as pulsed-mode operation.

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.

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.

Compensation of thermal lenses in high-power solid-state lasers

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 lenses in high-power lasers can be reduced significantly by means of thin layers of either liquids or gels. After a short review of the past developments we discuss the limits of lasers with intra-cavity thermo-optically self-compensated amplifiers (TOSCA). It is shown that for Nd:YAG typically one compensating layer is needed for every 6 cm of rod length.

Self-adaptive compensation of thermal lenses in an end-pumped Nd:YAG laser

In order to compensate for thermally induced lenses we have recently proposed and successfully demonstrated a new self-adaptive compensation scheme for transversally pumped laser rods. Now we show how this scheme can be simplified and adapted for end-pumped laser rods. The method is demonstrated with an end-pumped Nd:YAG laser and preliminary experimental results are presented.

Compensation of thermal effects in high-power solid state 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. The compensating (negative) lens is generated in a thin layer of liquid. We demonstrate that the proposed technique leads to a reduction of the thermal lens by more than an order of magnitude.

Measurement of White Light Chirp with Kerr Lens

The instantaneous transient Kerr lens in a transparent material offers a simple and efficient method to measure the spectrogram of a white light continuum. Even if the kernel of the spectrogram is not known very well, the instantaneous frequency may be extracted with high accuracy. It is shown that the knowledge of the phase modulation of a white light continuum simplifies the design of the prism compressors in a NOPA system. It also makes cross-correlation measurements at different frequencies in white light pump probe experiments obsolete.