Formation and Propagation of Needle Light Beams

Abstract

The field formed by an optical scheme of two axicons with a small difference in cone angles is investigated using analytical and numerical methods. The region of formation of a Bessel beam (BB) with a wide central maximum by this scheme is found. A method for obtaining needle beams characterized by a large diameter is proposed based on diaphragming of indicated BBs at the first minimum of the intensity distribution. It is shown that these beams, in comparison with limited Gaussian beams of the same power, have suppressed diffraction divergence. A comparison is made of the powers of the needle P_NB and limited Gaussian P_G beams incident on the receiving aperture with its different sizes and locations z, and it is shown that the P_NB/P_G ratio increases with increasing z. It is established that diaphragming of the BBs at the second or third minimum allows one to form light beams whose diffraction divergence is smaller than in the case of needle beams. The potential of using beams obtained by diaphragming a BB with a wide central maximum at the second minimum of the intensity distribution for probing objects located at a distance of up to tens of meters is shown.