Self-focusing of laser radiation in molecular gases

Optical properties of a nonequilibrium vibrationally excited gas

“…5, taken from [6], that taking account of the induced polarizability narrows the beam, where this narrowing increases as the laser radiation intensity grows.…”

“…Dependences of the light beam radius on the distance in a cuvette with the gas SF6 for different values of the laser radiation intensity: i) vacuum; 2) i0 mJ/cm2; 3) i00; 4) 300; 5) i J/cm=; points are data of an experifment [32], re, mm; z, cm. According to estimates [30] (see [31] also), the degree of kinetic cooling AT is 10 -I-10 -2 K for a C02-N 2 mixture at T = 300 K. Under the conditions considered in [28] ~n(AT) 1.3"10 -7 , while 6n(AT v) ~ 7.10 -7 . Therefore, self-focusing because of vibrational excitation will be more effective than because of kinetic cooling.…”

“…Plo + (1 + ~) Q1o + Wlo P10 and Q10 have their usual meaning of probabilities of vibrational-translational and vibrational-vibrational exchanges (see [7], say), and T V is the effective vibrational temperature determined by the vibrational energy reserve. Under saturation conditions (Wz0 >> Pz0, Ql0)~ 1 and the distribution function (19) goes over into ) and (an/ap)(~p/%T) (curves 2 and 2') as a function of v' for the gases CO, the ~3-mode of CO 2 and N 2 computed with (curves 1 and 2) and without (curves i' and 2') taking account of the dissociation process, at a p = 9.81.104 Pa pressure and T = 300 K gas temperature, an/aTv, (~n/ap)(ao/aT), deg -I.…”

“…The expressions (6) are obtained to the accuracy of second order terms in the expansion of the molecular Hamiltonian in an electric field in normal coordinates. Taking account of the higher derivatives, i.e., the next terms of the electrooptical anharmony, as well as corrections to the mechanical anharmony associated with replacement of a harmonic by an anharmonic oscillator, is executed in [5,8].…”

“…A detailed examination of self-focusing induced by vibrational excitation of molecules is presented in [6] in the "quasioptics" approximation, i.e., on the basis of a parabolic equation for the complex electrical field amplitude.…”