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Laser Window Surface Finishing and Coating Science

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Semiannual Technical rept. no. 2, 2 Jun-2 Dec 1975

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The objectives and the progress achieved in a program to study the surface finishing and coating of laser windows for high energy laser applications in the 10.6 micrometers 5.3 micrometers and 3.8 micrometers wavelength regions are reported. Recent chemical-mechanical optical polishing procedures use 1,2-propanediol, whose surface etch rate appears to match the rate of formation of damaged surface layers produced during polishing. Polycrystalline windows approximately 5 cm in diameter and 1 cm thick have been polished flat to 14 fringe in the visible with faces parallel to 2 arc sec, total optical absorption loss at 10.6 micrometers of 0.0007 for a 1 cm thick piece was measured after polishing. Recent coating efforts have placed emphasis on the use of three layer antireflection coatings produced in ultrahigh vacuum in an attempt to remove the absorption limitation of 0.1 per surface for the two layer coatings produced previously which have prevented the achievement of a program goal of 0. 1 coating loss per surface at 10.6 micrometers. With the new three layer coating designs it was possible to achieve coating absorption losses as low as 0.05 per surface for ZnSeThF4ZnSe designs. The rather high values of absorption index K.003 for ThF4 films used at 10.6 micrometers can now be incorporated in our new designs and we can still achieve coatings with less than 0.1 absorption losses.

Subject Categories:

  • Lasers and Masers
  • Manufacturing and Industrial Engineering and Control of Production Systems

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