A PECULIARITY OF DIFFRACTION MEASUREMENTS USING A GAUSSIAN LASER-BEAM

Numerical modelling of the Gaussian beam diffraction by a wire near th e Fraunhofer limit is presented. Two cases are considered: the case of the wire being on the axis of the beam and the case of the wire being off-axis, For the case where the wire is on the axis, the displacemen ts of the diffracted minima are calculated. For the off-axis case, the changes in the positions of the maxima and minima and the power densi ty are calculated. The conditions are determined at which the measurem ents made using a Gaussian beam can be calculated using the formula fo r plane waves. This work arises in connection with research being perf ormed into the Doppler spectrum of big particles. (C) 1998 Elsevier Sc ience Ltd, All rights reserved.