Thermal lensing and thermal aberration investigations in diode-pumped lasers

The thermal guiding effect plays a dominant role in beam formation of diode end-pumped lasers. Thermally induced aberrations occur for high pump density resulting in beam quality degradation. Thermal distortions in such lasers are investigated both theoretically and experimentally. It is found that severe wavefront distortions are generated outside the pump volume, whereas for a beam confined to pump volume the aberration effects are negligible. For high pump density these distortions result in an atypical caustics shape. This effect is examined for two cases: a fundamental mode laser pumped by a 2-W cw diode and a multimode laser pumped by a 10-W fiber-coupled bar. Two crystals-Nd:YAG and Nd.YVO4-are used as active media. The caustics shape observations and an interferometric inspection of wavefront distortion are performed. Satisfactory agreement between theory and experiments is achieved. (C) 1996 Society of Photo-Optical Instrumentation Engineers.