Diodengepumpte Laserverstärker mit flachen Lasermedien

Aachen / Publikationsserver der RWTH Aachen University (2007) [Dissertation / PhD Thesis]

Page(s): III, 133 S. : Ill., graph. Darst.

Abstract

Pulsed Laser-Oscillators are limited to a maximum output power depending on their regime of puls duration and repetition rate. The use of amplifiers enable higher power levels. The present theses reports on the development of laser amplifiers with a flat laser media and a special hybrid resonator, that can be used for a wide range of applications. The optical setup staring with the pump source, the active media and the resonator is described and methods for design and production are developed. Experimental results are given for a system of 10 ps puls duration and 50 W output power. The amplifier is running with high repetition rates as a quasi cw system and diffraction limited beam quality. The special slab shaped geometry of the crystal matches to the characteristic beam shape of high power diode laser bars. The radiation of the diode lasers is transformed to a homogeneous narrow line, that is imaged to the end face of the amplifier crystal. The use of a waveguide forms the homogeneous intensity distribution. Different waveguide concepts are introduced for the use of actively and passively cooled diode lasers. The pump unit is also usable for direct applications like laser welding of plastics or surface treatment of metal. The thermomechanical management of the slab crystal requires an efficient and constant cooling of two crystal side faces in order to achieve a minimum optical distortion of the amplifier beam. Heatsinks with different production techniques and geometries are described for the active conductive cooling of the laser crystal. The distribution of stress, expansion and temperature of the Nd:YAG and Nd:YVO4 crystals is calculated using FEM methods. The technological challenge is the packaging of the crystal and the heatsinks. The thermal contact of materials with different thermal properties has to enable a constant boundary condition in the contact plane on two faces of the crystal. Therefore different joining methods are tested and a new soldering method for the simultaneous soldering of two contact areas with a constant thickness of the solder gap is developed. The development of the components is the basis for the analysis of the amplifier system. Optical design methods are adapted for the calculation of the hybrid resonator layout and the beamshaping on the input of the amplifier. Experiments show, that the amplifier has two unique properties. Firstly high amplification factors of up to 300 where obtained. On the other hand the system can be designed to run very efficiently. With input powers of 2 W and output powers of 50 W, the amplifier shows behaviour of fully saturated amplification. The beam quality is determined to be better than M2<1,3. The optical-optical efficiency was measured to be 38% based on the absorbed pump radiation and 30% related to the total pump radiation. High pulsenergies are useful for frequency conversion. 80% of the output power can be converted to green laser radiation using an extra cavity nonlinear crystal. Experimental results proof, that scaling of the amplifier is not limited yet. A 12 mm wide Nd:YVO4 crystal is abele to produce 50 W output power. Nd:YVO4 crystals are available with a width of more than 30 mm in the market. On the assumption of double sided pumping and a 30 mm wide crystal 250 W output power could be possible. Power levels of 50 W where successfully used for display technology and micro machining. Higher power levels are useful for a wide field of material processing like fast laser ablation and structuring of metal surfaces.

Authors

Authors

Giesekus, Joachim

Advisors

Poprawe, Reinhart

Identifier

  • URN: urn:nbn:de:hbz:82-opus-18497
  • REPORT NUMBER: RWTH-CONV-123362