Abstract
The formation of the Doppler contour P (D)(?) of absorption lines upon the excitation of particles in the volume of a gas-dynamic beam by light propagating in a direction orthogonal (reduced) to the beam axis is analyzed. Integral representations of P (D)(?) are obtained for arbitrary relations between the nozzle outlet diameter D and the collimating aperture diameter B in the excitation region are obtained. An optimal configuration at which the reduced Doppler contour is the narrowest at a high density of beam particles is revealed to be B/D = 2.