Patent ID: 8265109

Claim:
An apparatus for focusing a beam for interaction with a film, the beam defining a short axis and a long axis, said axes being mutually orthogonal, said apparatus comprising: a short axis field stop positioned at a distance, d 1 , from said film; a first optic for focusing a laser beam at said field stop, thus producing a first line beam having a short axis width constrained by said field stop and being non-collimated along the long axis; a second optic positioned between said field stop and said film for focusing said first line beam onto said film in the short axis, thus producing said beam for interaction with the film, said beam also being non-collimated at the film in the long axis; and a detecting system to analyze light reflected from the film on an image plane, said image plane being positioned at a distance, d 2 , along a reflected beam path from said film, with d 2 substantially equal to d 1 , said detecting system analyzing said reflected light to determine whether said beam is focused in the short axis at said film.