Optical system comprising laser diode and diffractive collimator - uses two gratings impacted by cone of laser emission successively on opposite sides of axis

摘要

The point of emission (17) from the laser diode (10) lies on the axis (15) of symmetry of two diffraction gratings (11, 12) of concentric-ring structure in parallel planes. The axis (18) of the diode (10) is inclined (gamma) so that the collimated beam (19) emerges with an elliptical intensity distribution. The spatial frequency of the first grating (11) is such that its diffracted beam strikes the second grating (12) at a finite distance from the axis of symmetry (15). ADVANTAGE - Double-grating collimation produces beam of approximately circular section with brightness decreasing monotonically from centre towards edge.