Collimation testing using a circular Dammann grating

A novel technique for collimation testing with a circular Dammann grating is proposed. When the beam under test is incident on a one-order circular Dammann grating with limited aperture, double-humped radial rings will be generated at the back focal plane of a focusing lens. If the beam is collimated, the separation between the two rings will reach its minimal, otherwise the two rings will be apart from each other. Therefore, the degree of collimation of the tested beam can be estimated from the separation. The principle and experimental results of the method are presented. Owing to the simplicity and low cost of the method, it is a promising method for quickly checking the collimation of a laser beam.