Laser induced breakdown of diamond machined window surfaces

The effect of laser conditioning was examined by comparing thresholds and surface characteristics on areas of the surface exposed to nondamaging laser pulses (n-on-1 effect). The so-called n-on-1 effect was found to be wavelength selective with a much larger effect seen at 2.7 than at 3.8 micrometers. This result provides information on machining damage and may have important implications for laser processing as a possible means of improving the performance of machined optical surfaces. Surfaces prepared by precision diamond machining are compared with surfaces prepared by conventional polishing. The results indicate that the diamond machined surfaces have as high or higher failure resistance under high fluence loading as surfaces prepared using conventional techniques. Failure of both types of surfaces is strongly dependent upon surface structure and surface contamination. Laser conditioning experiments indicate that absorbed surface water is a significant contributor to surface failure under high fluence loading at 2.7 micrometers.