A laser is used to cut slots into a film deposited on a substrate so that a clean kerf is produced without harming the substrate. The laser cut vaporizes the film material as the removal mechanism and some of the vaporized material will redeposit over the surface of the film adjacent to the kerf. When the redeposited material is illuminated and viewed obliquely a series of light fringes can be observed. The laser focus is adjusted until the fringe pattern is symmetrical about the kerf. The laser power is adjusted until the fringes extend to about three times the kerf width on both sides of the kerf. This provides a precision nonsubjective means for adjusting laser focus and power.