The formation of the Doppler absorption profile upon optical excitation of particles in the volume of effusion or gas-dynamic atomic and molecular beams by laser light propagating in a direction orthogonal (reduced) to the beam axis is considered. The analytical expressions for P(ν) are obtained for different types of beams and the specific features of the reduced absorption profile are studied as functions of the beam parameters. The function P(ν)is shown to be considerably different from the standard Gaussian shape. It is demonstrated that the calculated absorption spectrum at the frequencies of the sodium resonance lines D_{1,2} agrees well with experiment.