Accession Number : ADP007071

Title :   High-Damage-Threshold Gratings using Coated Silicon Substrates,

Corporate Author : AT AND T BELL LABS HOLMDEL NJ

Personal Author(s) : Tom, H. W. K. ; Sher, M. H. ; Wood, O. R. ; Mansfield, W. M.

Report Date : 22 MAY 1992

Pagination or Media Count : 6

Abstract : High damage threshold gratings can be made by putting suitable coatings on silicon grating blanks. We expect several times improvement in the damage threshold for nanosecond laser pulses and similar improvements for 100 femtosecond laser pulses. We are currently investigating the manufacture of high damage threshold gratings using a novel idea. We are placing high reflectivity coatings on holographically patterned Silicon grating blanks. This approach provides three principle advantages compared to current gratings made by placing a thin metallic layer over holographically patterned photoresist on glass substrates. First, advanced lithographic and processing techniques for Si make possible the fabrication of arbitrary grating groove profiles with holographic registration across large areas. Second, metal-Si gratings should not be limited by damage at the metal-silicide interface because Si is an efficient thermal conductor and the damage threshold of metal silicide is > 400 C. This is in great contrast to metal-photoresist gratings which damage at the metal-photoresist interface when temperatures exceed 100-200 C. Third, extremely efficient gratings can be fabricated using enhanced metallic and dielectric coatings (99% reflectivity) on blazed gratings (ie., triangular groove profiles). These advantages make us believe damage thresholds comparable to those of bulk metals (300 mJ/cm2) are obtainable. For dielectric enhanced metallic coatings, several times the bulk and metal damage threshold should be possible.

Descriptors :   *PULSED LASERS, *COHERENT OPTICAL RADIATION, *OPTICAL COATINGS, SILICON, GRATINGS(SPECTRA), PROTECTIVE COATINGS, REFLECTIVITY, PHOTORESISTORS, SHORT WAVELENGTHS, COHERENT RADIATION, DAMAGE CONTROL, DIELECTRIC FILMS, GOLD, SYMPOSIA.

Subject Categories : Coatings, Colorants and Finishes
      Optics
      Lasers and Masers

Distribution Statement : APPROVED FOR PUBLIC RELEASE