Abstract

Measurement of the laser beam diameter is essential for estimation of the beam divergence, in optical disks, and metrology application utilizing laser sensors. While the rectangular (Ronchi) ruling of a particular period (L) is capable of estimating the beam radius (r_o) for r_o/L ranging from between 0.2 and 1.2, triangular and sinusoid gratings¹ extend the range to a much smaller radius compared to the grating period. The upper limit of the beam diameter measurement has recently been improved by formulation of an aperiodic ruling.² However, because of the rectangular (discontinuous) nature of the grating, the lower values of the beam radius cannot be measured. In this work, we propose a novel grating with periodic logarithmic transmission characteristics that are capable of extending the range to both higher and lower values of the beam radius. Our proposed logarithmic periodic grating provides a linear variation of k for r_o/L between 0 to 1.2. Using two or more gratings it is possible to extend the beam radius on a truly continuous scale. Gratings of such characteristics can be fabricated by contact screen method.

© 1991 Optical Society of America