CONTINUOUSLY TUNABLE HIGH-PRESSURE CO2-LASER FOR SPECTROSCOPIC STUDIES ON TRACE GASES

A high-pressure CO2 laser with unique characteristics in terms of cont inuous tunability and emission bandwidth is presented, It is operated at a pressure of 11.5 bar and transversely excited by short, high-volt age pulses generated by a double LC inversion circuit, Auxiliary disch arges parallel to the electrodes provide a sufficient free-electron de nsity through UV ionization of the laser gas mixture. The laser resona tor consists of a near-grazing-incidence grating setup in which the gr ating is positioned at a large incidence angle of 77 degrees. A theore tical model for the calculation of the emission bandwidth is presented and its predictions are compared to direct measurements and show exce llent agreement, The achieved very narrow bandwidth off 0.018 cm(-1) c onstitutes the ultimate wavelength resolution of any detection system using this laser as radiation source, It allows the resolution bf any fine structure in the spectra of absorbing gases at atmospheric pressu re. Continuous tunability has been achieved over 76 cm(-1) between 932 cm(-1) and 1088 cm(-1) with minimum pulse energies in excess of 10 mJ . The narrow band-width precludes the occurrence of mode-pulling effec ts so that the laser exhibits a linear wavelength tuning behavior thro ughout the entire emission range, The calibration of the laser wavelen gth is performed by photoacoustic measurements on low pressure CO2 gas . An absolute accuracy of +/-10(-2) cm(-1) is achieved, A great potent ial improvement in detection selectivity can thus be expected from a s cheme with the high-pressure CO2 laser as radiation source.