A spectrophone and a CO2 laser source were used to determine the absorption coefficients of NH3 at seventy-seven laser lines in the 00°1–02°0 band at 9.4 μm and the 00°1–10°0 band at 10.4 μm. The NH3 was buffered with N2 to 1 atm at 295 K; its concentration ranged from 30 ppm to 200 ppm. The absorption coefficients and their probable errors are tabulated.

Photoacoustic spectroscopy of NH 3 at the 9-μm and 10-μm 12 C 16 O 2 laser wavelengths

Propagation of a collimated, pulsed laser beam in an absorbing medium has been investigated theoretically. The energy absorbed by the medium causes heating, leading to an index-of-refraction change that causes self-defocusing. The analysis is based upon the scalar wave equation in the Fresnel limit and the linearized equations of hydrodynamics. The governing equations are integrated numerically using a stable, explicit, finite-difference method. Numerical results for gaussian beams are presented in the form of irradiance profiles as functions of normalized range and time. An initially gaussian beam distribution is deformed into a relatively flat distribution with the peak irradiance near the edges of the beam.

Propagation characteristics of collimated, pulsed laser beams through an absorbing atmosphere

Theoretical and experimental studies have been carried out to determine the importance of mechanical turbulence, i.e., velocity fluctuations, on the propagation of high power cw CO(2) laser radiation in the atmosphere. The experimental results were obtained using artificially generated turbulence and show, in agreement with theory based on a diffusion model, that the turbulence tends to replace the asymmetric bending, focusing, and spreading by the mean wind with a symmetric blooming. For sufficiently strong velocity fluctuations, say, greater than two to three times the mean velocity, the turbulence can reduce thermal blooming effects and increase the beam irradiance. Smaller turbulence levels, however, may actually result in decreasing the beam irradiance somewhat. From these results and estimates of the properties of turbulent diffusion in the atmosphere it appears that under typical conditions the mechanical turbulence will not significantly reduce the wind-dominated thermal distortion effects.

Turbulence Effects on Thermal Blooming

The Possibility of the application of the finite element method to some problems of nonlinear optics is investigated in this paper. The self-action of a light beam in a nonlinear medium is considered. The general approach to the cretion of conservative computation schemes is presented, based on varitional principles. Definite schemes, which are applicable for the problem of thermal self-action, are described in detail both in the case of cylindrical and or rectangular co-ordinates. The accuracy and convergence of the models are analysed. The results of computation of the self-action problems in motionless and moving media are presented.

The finite element method in problems of nonlinear optics

This paper describes the contents of a general "four-dimensional" computer code for the transient thermal blooming of multi-pulse laser beam propagation. The solutions of the scalar wave equation in Fresnel approximation and the hydrodynamic equations are obtained by means of the discrete Fourier transform method. Based upon the scalar wave equation and the equations of hydrodynamics, the paper makes a model for collimated multi-pulse laser, simulates the
transient thermal blooming numerically, and gives the laser beams irradiance distribution by changing respectively the
value of the propagation distance, the pulse-repetition rate, the power, and the time. Besides, we simulate the
thermal blooming of cw in order to make a contrast with multi-pulse laser. The results show multi-pulse lasers minimize 
thermal-blooming; if the pulse-repetition rate decreases, thermal blooming decrease, and the quality of the beam is better.

Transient Thermal Blooming of Collimated Multi-pulse Laser Propagation in Atmosphere

Theoretical evaluation of the effects of absorption at 10.6 μm on the diffracted field has been investigated. The physical model of the nonlinear interaction process includes the effects of absorption by CO2 and H2O, transverse flow and vibrational relaxation effects associated with atmospheric absorption by CO2. The analysis is based upon the scalar wave equation in the Fresnel limit and the governing equation is integrated numerically using a stable, finite difference method. Diffraction patterns in the far field for an unfocused beam and at the focal point for a focused beam are presented. The atmosphere acts as a nonlinear lens with aberrations and the irradiance distributions exhibit a complicated filamentary pattern at the focal point.

Effects of Nonlinear Refraction at 10.6 μm on the Far-Field Irradiance Distribution*

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Effects of Nonlinear Refraction at 10.6 μm on the Far-Field Irradiance Distribution*