Ultrahigh-Sensitivity High-Speed Laser Spectrocopsy of Radicals and Molecules

Abstract

The probability of exciting the 2s state of hydrogen in an exchange collision between a proton and a hydrogen atom has been measured by Bayfield. Calculations are carried out which give some evidence on the mechanism responsible for the experimental observations.

Study of the HNO + HNO and HNO + NO reactions by intracavity laser spectroscopy

“…This method was employed for quantitative kinetic measurements by Sarkisov et al [12]. Since then the possibilities and advantages of this method's kinetic applications were demonstrated in several works [13][14][15][16][17][18]. Only a brief summary of the apparatus and technique used will be given here.…”

“…The laser output spectra with absorption lines of HNO and NO2 were photographed on a spectrograph with a resolution of about 0.05 A. Microdensitometer tracings of spectra were processed by the technique suggested by Belikova et al [17]. This processing was shown [14, 15,17] to allow the concentration of the species examined to be determined in arbitrary units. Figure 2 shows the microdensitometer trace of the HNO spectrum.…”

Damage in Laser Materials

“…(6) through (9). At the high intensity levels which can be reached in lasers, conduction electrons may also be created by the simultaneous absorption of several photons [18,19]-Various schemes have been proposed for two-, three-, and four-photon absorption in ruby [15,[19][20][21][22][23] and four-photon absorption (of ruby radiation) in glass [24]. Since the probability for n-photon absorption increases with decreasing n, anything which affects the number of photons required to get electrons into the conduction band will influence the probability of the multiphoton process.…”

“…-C,g (n )X^/At. (21) a^o Equations (20) and (21) predict a constant total power threshold [34] for At »t and an energy density threshold varying inversely with At for At « T. To illustrate this behavior, curves based on calculations for ruby laser radiation in BK-7 glass [40] are plotted as solid lines in figure 5 along with a data point for damage accompanied by self-focusing from a 40ij, initial beam radius [41]. The exact agreement between this measurement and the calculations is probably fortuitous since the damage level should exceed the trapping threshold in order to reduce the beam cross-section significantly The beam must also travel a finite distance in the material for self-focusing to have a notable effect An approximate focusing length can be defined by equating the optical path length (n^+ An)L£ along the beam axis with the path length n^(L^^+^h^^^^from the beam perimeter to the axis, where An is the change in refractive index on axis [42].…”

“…The exact agreement between this measurement and the calculations is probably fortuitous since the damage level should exceed the trapping threshold in order to reduce the beam cross-section significantly The beam must also travel a finite distance in the material for self-focusing to have a notable effect An approximate focusing length can be defined by equating the optical path length (n^+ An)L£ along the beam axis with the path length n^(L^^+^h^^^^from the beam perimeter to the axis, where An is the change in refractive index on axis [42]. Using appropriate limiting forms for An [40] and requiring to equal the sample length L, gives Large local intensity variations over the beam cross-section can cause localized self-focusing resulting in the formation of multiple filaments 2,2 ---•°= At/L (22) d b^'…”