Absorption line parameter measurements using laser spectroscopy.

An analytical method is described for obtaining the precise location of an absorption line and the pressure broadening coefficients due to self-broadening or foreign gas broadening from experimental measurements using a laser operating on a single line near the absorption line. These absorption line characteristics are obtained from the pressure dependence of the transmittance of the laser radiation for the gas of interest, the analysis involving a least squares fit to a family of Lorentz curves. The method includes a computer search for the region of best fit to the Lorentz profile and provides both the values of and errors in the above coefficients. The pressure broadening coefficient obtained is the same as for the more general Voigt curve. The method is applied to the absorption line of vinyl chloride near 27.972 microm and of methane near 3.392 microm and the results compared with a graphical fit to a Voigt profile. The self-broadening coefficients obtained were alpha = 0.15 x 10(-3) +/- 0.97 x 10(-4) cm(-1) Torr(-1) for vinyl chloride and alpha = 0.14 x 10(-3) +/- 0.46 x 10(-4) cm(-1) Torr(-1) for methane. The separation between the helium-neon laser line at 2947.903 cm(-1) and the methane absorption line at 2947.888 +/- 0.015 cm(-1) was found to be 0.21 x 10(-2) +/- 0.15 x 10(-2) cm(-1).

Excitation processes and relaxation rates in the pulsed water vapor laser.

This paper presents an experimental study of time-resolved gain in H(2)O, H(2)O-He, and H(2)O-H(2) mixtures as a function of gas composition and excitation current. Utilizing the fast rising (~70 nsec) pulse from H(2)O-He laser as a probe, the amplifier gain was measured with a time resolution of about 100 nsec. The gain was observed to follow the excitation current pulse rather closely indicating that population inversion was established in times less than 100 nsec. This suggested that excitation was most likely by means of rapid cascading from higher levels and/or by direct electron impact. The gain was found to be describable by a two-level rate equation model containing one dominant relaxation rate and assuming immediate excitation of the levels involved by inelastic collisions with electrons. With pure H(2)O, the relaxation rate was proportional to pressure to within 10%, indicating that the upper level was de-excited primarily by c llisions with other H(2)O molecules. At a pressure of 1 Torr the relaxation rate in pure H(2)O was 0.35 +/- 0.05 for the 28-microm transition. The addition of small amounts of foreign gases was observed to increase this relaxation rate, consistent with the measured decrease in the amplifier gain. By subsequently increasing the water vapor pressure it was found possible to optimize the gain at an enhanced level over the pure H(2)O case. The peak gain obtained in water vapor at 1000 A was 0.34 m(-1). Under foreign gas addition this increased to 0.68 m(-l) for the same peak current. In this case the relaxation rate, as a function of the foreign gas (He or H(2)) pressure, remained constant to within 10%, suggesting that these gases at higher concentrations may enhance the system gain by altering the discharge conditions without appreciably collisionally de-exciting the upper laser level.

Analysis of gain measurements of a pulsed two-level laser system.

A fast and convenient method for the extraction of basic constants from time resolved laser amplifier gain measurements is described. The method is based on the assumption of a two-level laser system having direct electron excitation of the levels involved. The experimentally measured pulsed discharge current waveforms and time resolved gain curves are analyzed by a digital computer and fitted to the above model.