The influence of laser cavity gaseous impurities on the performance of an industrial CO2 laser (Part II)

Abstract

Contamination in the cavities of high power industrial CO2 lasers is a cause of laser performance degradation. Such degradation can result in laser downtime and significant loss of productivity. The laser cavity gas supply can contribute to this contamination, but there is confusion about the level of gas impurity concentration which can cause a degradation processes. The overall objective of this investigation was to study the effects of cavity gas contaminants on the performance of an industrial fast-axial-flow CO2 laser.A 3 kW fast-axial-flow CO2 laser operated for 2100 hours prior to this investigation was employed in a series of gas contamination experiments. The operating power was selected as 1500 W. After cleaning the laser cavity, the, absorptivities in the output coupler and rear mirror were measured after laser operation using both ultra-higg-purity laser cavity gases (99.999%) and premixed contaminated helium (100 ppm, 1000 ppm and 5000 ppm for C3H8, C2H4, CH4 and O2). The output powers were also measured during laser operation.Increased absorptivities in the output coupler were observed with both hydrocarbon and oxygen impurities compared to those with ultra-high-purity gases. The increased absortivities in the output coupler and rear mirror seem to correlate with the total carbon contents in the laser cavity due to the gaseous hydrocarbon impurities. Deposition on the surfaces of comer mirrors were identified as carbon using energy dispersive electron spectroscopy analysis after operating laser using 5000 ppm ethylene in helium. Several flakes of deposited carbons were also identified on the surface of the NaCl window inside the resonator after operating the laser using ultra-high-purity gases for 1 hour and 5000 ppm propane in helium for 3 hours. 1000 ppm oxygen in helium resulted in an increase of 1.4% in the output power (4.8% for 5000 ppm oxygen). Erosion in the output coupler was observed with 5000 ppm oxygen. 1000 ppm of propane resulted in a decrease of 17% in the output power. A 44.8% of power drop was observed when using 5000 ppm propane. All impurities used in this investigation had negative effects on laser-cavity optical elements compared to ultra-high-purity gases. The only mixture used in this investigation with acceptable long term effects had less than 10 ppm (99.999% ultra-high-purity) of all impurities.Contamination in the cavities of high power industrial CO2 lasers is a cause of laser performance degradation. Such degradation can result in laser downtime and significant loss of productivity. The laser cavity gas supply can contribute to this contamination, but there is confusion about the level of gas impurity concentration which can cause a degradation processes. The overall objective of this investigation was to study the effects of cavity gas contaminants on the performance of an industrial fast-axial-flow CO2 laser.A 3 kW fast-axial-flow CO2 laser operated for 2100 hours prior to this investigation was employed in a series of gas contamination experiments. The operating power was selected as 1500 W. After cleaning the laser cavity, the, absorptivities in the output coupler and rear mirror were measured after laser operation using both ultra-higg-purity laser cavity gases (99.999%) and premixed contaminated helium (100 ppm, 1000 ppm and 5000 ppm for C3H8, C2H4, CH4 and O2). The output powers were a...