Effects of the velocity dependence of the collision frequency on the Dickeline narrowing

The effect of the velocity (v) dependence of the transport collision freque ncy nu (trv) on the Dicke line narrowing is analyzed in terms of the strong -collision model generalized to velocity-dependent collision frequencies (t he so-called kangaroo model). This effect has been found to depend on the m ass ratio of the resonance (M) and buffer (M-b) particles, beta = M-b/M: it is at a minimum for beta < 1 and reaches a maximum for beta greater than o r similar to 3. A power-law particle interaction potential, U(r) proportion al to r (-n), is used as an example to show that, compared to nu (trv)(v) = const (n = 4), the line narrows if nu (trv)(v) decreases with increasing v (n < 4) and broadens if nu (trv)(v) increases with v (n > 4). At beta grea ter than or similar to 3, the line width can increase [compared to nu (trv) (v) = const] by 5 and 12% for the potentials with n = 6 and n greater than or similar to 10, respectively; for the potentials with n = 1 (Coulomb pote ntial) and n = 3, it can decrease by more than half and 6%, respectively. T he line profile I(Omega) has been found to be weakly sensitive to nu (trv)( v) at some detuning Omega (c) of the radiation frequency Omega . Dicke line narrowing is used as an example to analyze the collisional transport of no nequilibrium in the resonance-particle velocity distribution in a laser fie ld. The transport effect is numerically shown to be weak. This allows simpl er approximate one-dimensional quantum kinetic equations to be used instead of the three-dimensional ones to solve spectroscopic problems in which it is important to take into account the velocity dependence of the collision frequency when the phase memory is preserved during collisions. (C) 2001 MA IK "Nauka/Interperiodica".