Abstract

A modified method of testing laser beam collimation is presented. The method is based on self-imaging coupled with the Moiré phenomenon. A Ronchi grating of low frequency (about 50 to 100 lines/in.) is placed in the beam to be tested such that the grating lines make an angle δ with the horizontal. Self-images (Talbot images) of this grating are formed at certain well defined planes. A right angled prism is used in the retroreflecting mode to project the folded self-image onto the actual grating. The grating lines in the projected self-image would make an angle minus δ with the horizontal. The Moiré fringes are observed through a beam splitter placed between the grating and the collimating lens. For a collimated beam the Moiré fringes are parallel to the roof-edge of the prism, which is seen as a bright line; otherwise, they are rotated with respect to this reference orientation. The technique has a built-in reference and does not require precise alignment or measurement of the grating orientation.

© 1992 Optical Society of America