In general, the temperature distribution in Nd : YAG laser rods deviates from a parabolic functional form due to the temperature dependence of thermal conductivity and the inhomogeneity of pumping light distributions. An analyti- cal expression is derived which relates the resulting radially dependent refractive power to the shape of the pumping light distribution. To first order, the refractive power has a para- bolic radial dependence and this spherical aberration consid- erably affects the laser's output characteristics. The perfor- mance of both stable and unstable resonators is investigated theoretically by numerically solving the Fresnel-integrals, in- cluding the amplification, the refractive power and the aber- ration of the rod. High output power and good beam quality cannot be achieved simultaneously when aberration is present. Experiments for both resonator types were performed with a pulsed Nd : YAG laser capable of a maximum output of 320 watts of average power.

http://ieeexplore.ieee.org/iel1/3/6339/00247707.pdf

Influence of Spherical Aberration of the Active Medium on the Performance of

In general, the temperature distribution in Nd:YAG laser rods deviates from a parabolic functional form due to the temperature dependence of thermal conductivity and the inhomogeneity of pumping light distributions. An analytical expression is derived which relates the resulting radially dependent refractive power to the shape of the pumping light distribution. To first order, the refractive power has a parabolic radial dependence and this spherical aberration considerably affects the laser's output characteristics. The performance of both stable and unstable resonators is investigated theoretically by numerically solving the Fresnel-integrals, including the amplification, the refractive power and the aberration of the rod. High output power and good beam quality cannot be achieved simultaneously when aberration is present. Experiments for both resonator types were performed with a pulsed Nd:YAG laser capable of a maximum output of 320 watts of average power. >

Influence of spherical aberration of the active medium on the performance of Nd:YAG lasers

Many laser applications require high beam quality at high output power and a broad variation of the output power. The ratio of power variation Delta P/sub out/ to beam parameter product theta /sub m/-w/sub m/ for a single rod inside a stable resonator is a constant which depends on the intrinsic crystal parameters and the slope efficiency only. A broad range of the output power causes a large beam parameter product, i.e. a low beam quality. By using several rods inside the same resonator and by a suitable choice of rod position and resonator parameters, the output power range can be increased without reducing the beam quality. In the same way, the beam quality can be improved without reducing the output power. The details of multirod systems are discussed and compared to experimental results. >

Multirod resonators for high-power solid-state lasers with improved beam quality

Thermally-induced spherical aberration in Nd:YAG rods is investigated. Attention is concentrated on the so-called "intensity moment formalism" to analyze the beam-quality parameter of the emitted laser beams. A number of resonance conditions that certain beam-shape parameters of any stable laser mode should fulfill are also derived, and a comparison with previously reported numerical results is presented.

Beam-quality changes generated by thermally-induced spherical aberration in laser cavities

The thermal lensing properties of stable and unstable resonators are compared and rules are given for the design of optimized unstable resonators containing a focusing rod. Experimental verification with a high-power Nd: YAG system proved that for unstable resonators the restricting relationship between beam quality and output power no longer holds. Careful resonator design enables high output power to be extracted with unstable resonators without destroying the output couplers.

High-power solid-state lasers with unstable resonators

This paper deals with the focusing of multimode radiation. Two special types of resonator are presented: type 1 produces constant beam radius at varying internal thermal lensing and type 2 has, under some conditions, constant beam divergence. It will be shown that by suitable imaging, a focus of constant diameter and constant position can be realized, if the output beam of the laser is varying in diameter only. Variation of the output beam divergence can be compensated by a different optical system.

R. Iffländer

Papers

Focusing of multimode laser beams with variable beam parameters