Some techniques for laser spectroscopy of gaseous media

Two laser-spectroscopic techniques are examined with which undistorted absorption spectra of materials in the gas phase can be obtained with an instrument resolution of the order of 0.001/cm. In the first case (high-speed laser spectroscopy), spectroscopic measurements are reduced to precision measurements of the wavelength at which the laser operates and the ratio of the intensities of the probing and investigated signals. Three methods for measuring this ratio are proposed which allow the absorption coefficient to be recorded with a sensitivity of 10 to the -6th power per cm. In the second case (active laser spectroscopy), the sensitivity range is expanded to 10 to the -9th power per cm by introducing a multiple-pass optical cell with the investigated gas into the laser cavity. The absorption spectrum is then measured on the basis of changes in the laser-emission spectrum. Recommendations for improving the operation of laser spectrometers are given which can reduce the error in measuring absorption spectra of gaseous media to no more than 10%.