A High-pressure Carbon Dioxide Gasdynamic Laser
National Aeronautics and Space Administration, 1973 - Carbon dioxide lasers - 20 pages
A carbon dioxide gasdynamic laser was operated over a range of reservoir pressure and temperature, test-gas mixture, and nozzle geometry. A significant result is the dominant influence of nozzle geometry on laser power at high pressure. High reservoir pressure can be effectively utilized to increase laser power if nozzle geometry is chosen to efficiently freeze the test gas. Maximum power density increased from 3.3 W/cu cm of optical cavity volume for an inefficient nozzle to 83.4 W/cu cm at 115 atm for a more efficient nozzle. Variation in the composition of the test gas also caused large changes in laser power output. Most notable is the influence of the catalyst (helium or water vapor) that was used to depopulate the lower vibrational state of the carbon dioxide. Water caused an extreme deterioration of laser power at high pressure (100 atm), whereas, at low pressure the laser for the two catalysts approached similar values. It appears that at high pressure the depopulation of the upper laser level of the carbon dioxide by the water predominates over the lower state depopulation, thus destroying the inversion.
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10-percent carbon dioxide 50-percent helium AIAA Ames Research Center area ratio beam splitter calorimeter carbon dioxide concentration carbon dioxide gasdynamic caused depopulating the lower deterioration of laser dioxide gasdynamic laser discussed dissociation expansion nozzle experiments extreme deterioration germanium go to zero helium-neon laser high pressure higher reservoir pressure hydrogen indium antimonide instantaneous laser power laser beam Laser power variation longer relaxation low pressure lower state depopulation mass flow maximum power Moffett Field mole fraction nitrogen to helium nozzle geometry nozzle reservoir operate optimization optimum temperature Oscilloscope output mirror population inversion power at high pressure and temperature pulse shape rate of expansion ratio of nitrogen reflected-shock reservoir conditions reservoir temperature shock tube shown in figure slug small throat spatially averaged power standard optical cavity test gas test gases test regimes upper laser level upper state depopulation Usable test variation of laser vibrational energy density vibrational relaxation water vapor