Hole gratings for laser damage testing

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Abstract
The use of hole gratings in small-spot laser damage testing is discussed. If the intensity loss due to the transmission of the grating and due to the production of several spots can be tolerated, a hole grating is shown to increase the ease of establishing a damage threshold by the production of spots with a wide range of intensities whose ratios are well understood. It allows the investigation of defect-related damage since several regions are illuminated with equal intensities, and it permits the investigation of the effects of several closely spaced simultaneous illuminations. Several types of arrays of circles and ellipses are investigated, and the effects of hole size, hole spacing, hole shape, and elliptical hole orientation are discussed. The effects of apertures of the grating are also discussed. Two methods of suppression of diffraction spots lying outside the Airy disk are described and illustrated which utilize distributions of either circular hole sizes or of elliptical hole orientations. Two arrays are used in damage tests of metal surfaces to illustrate their use.