Heinz P. Weber

Beam-quality improvement of a passively Q-switched Nd:YAG laser with a core-doped rod

We present experimental results that demonstrate the great efficiency of a core-doped Nd:YAG rod (a hexagonal Nd:YAG core surrounded by undoped YAG) in producing high output power and excellent beam quality. An additional improvement in beam quality is clearly observed when the core-doped rod is used in combination with a LiF:F(2)(-) crystal, which acts as a passive Q-switching element. This improvement is quantified by beam-propagation factors as low as M(2) approximately = at a maximum average output power of 9 W. We show that transversally pumped core-doped rods with the addition of LiF:F(2)(-) crystals fulfill the requirements for high-beam-quality, scalable, compact all-solid-state lasers in passively Q-switched operation.

High Power Light-Transmission in Optical Wavequides

Optical lightguides (fibers) allow to guide light in a flexible manner to a working area. Such lightguides are however enherently very narrow structures, which leads to extremely high intensities in the guides even for moderate powers. The limiting processes for undisturbed transmission are described and for a variety of parameters and situations the corresponding numerical values are given, as far as available. The high intensity processes recently led to several interesting new device-applications.

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.

Novel optical resonators and thermal lensing

The maximum power range over which a laser resonator supports stable oscillation is mainly determined by the (thermal) material consists of the active medium and by the cooling scheme. The power range for stable fundamental-mode operation can be shifted to higher powers with special cavity designs and intra-cavity optics but the width of the stability range will be unaffected. Moreover, increasing the pump intensity in the active medium also aggravates the aspheric components of the thermally induced distortions. It is therefore of major importance to analyze these thermal effects when developing novel resonators. We present investigations on thermally induced distortions and on a novel multi-rod laser cavity, known as the variable- configuration resonator (VCR). The thermal effects have been studied both numerically and experimentally. We present a comparison of various pumping and cooling schemes. It is found that composite rods provide the most effective cooling for end-pumped lasers. The VCR was developed to scale the power range of fundamental-mode lasers. Due to its capability to run either as a Fabry-Perot resonator or as a ring cavity it overcomes the stability problems associated with conventional multi-rod resonators and allows for a novel Q-switching technique.

Self-adapting thermal lens to compensate for the thermally induced lens in solid state lasers

The thermally induced lens is a critical issue in high-power diode-pumped solid-state lasers. A self-adaptive scheme to balance the thermal lenses in laser resonators is presented. The requirements for the thermo-optical self-adaptive element and its influence on the resonator are discussed. With an appropriate compensating element and the correct resonator design, constant beam parameters are expected to be achieved over a pump range of several kilowatts.

High-efficiency high-power cw solid state lasers for material processing

The maximum power range over which a laser resonator supports stable oscillation is mainly determined by the material constants of the active medium and by the cooling schemes. The power range for stable fundamental-mode operation can be shifted to higher powers with special cavity design and intra-cavity optics but the width of the stability range will be unaffected and can be enlarged only with adaptive optics. We present investigations on a multi- rod laser cavity and a high-power side-pumped laser system. In order to obtain constant beam parameters with varying power we prose a novel self-adaptive method to compensate for the power-dependent thermal lenses in high-power lasers.