Formation and Propagation of Needle Light Beams
摘要
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 by this scheme of a Bessel light beam (BLB) with a wide central maximum is found. A method for obtaining wide-diameter needle beams is proposed based on diaphragming of the indicated BLBs at the first minimum of the intensity distribution. It is shown that these beams have suppressed diffraction divergence as compared to limited Gaussian beams of the same power. The powers of the needle PNB and limited Gaussian beams PG incident on the receiving aperture with its different sizes and locations z are compared. It is shown that the PNB/PG ratio increases with increasing z. It is established that diaphragming of the BLBs at the second or third minimum allows light beams with diffraction divergence smaller than in the case of needle beams to form. The potential of using beams obtained by diaphragming a BLB with a wide central maximum at the second minimum of the intensity distribution for probing objects at distances up to tens of meters is demonstrated.