Diffusionsgekühlte, koaxiale CO 2 -Laser mit hoher Strahlqualität

In this work,diffusion cooled CO2-lasers with coaxial structure are researched. The research includes all essential aspects that are relevant for a laser that can be utilized industrially: plasma physical conditions in the gas discharge, the resonator, and the suitable beam forming. Extensive research was conducted on rf-excited CO2-laser plasmas. Plasmas, barely researched until now, with large gap sizes d=6mm and low rf-power-density p_HF=5W/cm3 were researched. At the same time,two different spectroscopic methods were used to observe the dissociation of the CO2-molecules occurring in the laser plasma time-resolved and simultaneously with the changes of the laser power. With this, for the first time,the effects of gas additions such as Xe, H2, H2O and CO as well as catalysts on the dissociation and recombination rates were systematically measured. Aside from the research of the gas composition,the spectroscopic methods allowed measurement of the gap temperatures and thus, indirectly the quantification of the Ohmic losses occurring at the sheath of the gas discharge. With the utilized rf-frequency of 27MHz, sheath losses of 25 to 40% result,but suitable electrode coatings can reduce those sheath losses. Furthermore, this work theoretically describes and experimentally researches radial stable, azimuthal instable resonators. Specifically, the lacking mode and power stability as well as adjustment sensitivity of the helix-torus resonator, suggested by Ehrlichmann, are eliminated through the further development to a helix-axicon resonator. This helix-axicon resonator is described in detail regarding its characteristics. The axicon effects a doubling of the resonator length and thus a reduction of the power fluctuations. The retro effect of the axicon simultaneously produces a reduction of the adjustment expenditure. It was possible to calculate the outcoupled beam from the resonator with numeric resonator modeling in good conformity with the experiment. While in radial direction a good mode form and beam quality is already achieved, the azimuthal direction must still be brought into the desired Gauss-like form through a spatial filtering. The layout of a suitable telescope of four cylinder mirrors is described which transforms the generally astigmatic emitting beam into an almost round, stigmatic beam with beam qualities of M2=1,2 in all directions. The essentially azimuthal polarization distribution of the beam emitting from the helix-axicon resonator remains during the forming in the telescope and results in a space-wise varying polarization direction over the beam expansion. Possibilities for the transformation into a purely linear polarization via a topological transformation of a 90-degree-deflecting axicon are discussed.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Schulz, Joachim

Contributors dc:contributor

• Poprawe, Reinhart

• info:eu-repo/classification/ddc/530
• Physik
• Kohlendioxidlaser
• Hochfrequenzentladung
• Kühlung
• Diffusion
• Strahlqualität

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-119034%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:56960