Effects of 106-μ Laser Induced Air Chemistry on the Atmospheric Refractive Index

Abstract

Atmospheric absorption of 10.6-mu radiation can either heat or cool the air, depending upon atmospheric conditions. Absorption by CO(2) is essentially from the (100) to the (001) states. The depleted (100) state is rapidly replenished by energy transfer from translation, cooling the atmosphere. The (001) state slowly transfers energy through the N(2) back to translation, eventually heating the atmosphere. Cooling increases the density and index of refraction, and the resulting gradient tends to focus a gaussian beam. This partially offsets the usual heating effects and associated ray divergence.

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

“…These figures show that the amplitude of the PA signal increases with the buffer radius and that the highest absolute sensitivity is obtained for the largest radius (60 mm) except for the 0.97-1.07 m −1 absorption coefficient range. At low absorption levels (below 0.05 m −1 ) and without kinetic cooling effect [24,[38][39][40], the PA signal is proportional to the absorption of the compound present in the cell [1]. At higher absorption levels, the PA signal is no longer proportional to the absorption coefficient but shows a maximum (Fig.…”

Characterization of a precise phase-reading, CO2laser-based photoacoustic spectrometer

“…However, if CO 2 and N 2 are present, the Fermi coupling between the 001 level of CO 2 and the first excited vibrational state of N 2 , determines an intermolecular energy exchange that reduces the heating rate. This process is referred as "kinetic cooling" [4] and the associated photoacoustic signal shows a noticeable phase shift compared to a substance that relaxes fast.…”

“…where k 1 , k 2 , k 3 , k 4 and k 5 are the rate constants, in units of m 3 /s, of the main V-V processes between the different species in the atmosphere.…”

An Analysis of Mathematical Transformations and a Comparison of Numerical Techniques for Computation of High-Energy CW Laser Propagation in an Inhomogeneous Medium

“…In (2-4) the two quantities in the complex exponential represent the phase arising from the laser cavity and the focusing optics, respectively. It should be noted that in Equation (2-3) we have neglected the so-called kinetic cooling phenomenon, 23 since this effect is insignificant for ground-based lasers. This effect can nevertheless be brought into this model without change in the basic nature of the algorithm, since it merely affects a quadrature formula.…”

“…The sequence of relations, Equations (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) to (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23), when performed for k = 1,2,...K, comprises the first half of the fractional step method. It should be noted that all quantities are complex and that complex arithmetic is implied throughout.…”