Antireflection Coatings for Calcium Fluoride Laser Windows for 5.3 Microns.
Abstract
Four distinct antireflection (AR) coatings and half-wave coatings of their constituent coating materials were evaluated for 5.3 microns on CaF2 and BaF2 substrates. The coating materials were lead and strontium fluoride, thorium tetrafluoride, and zirconium dioxide. The coatings were evaluated with regard to absorption, peak transmission, bandwidth, redisual strain, and adhesion. A PbF2/ThF4 AR design had an absorption per surface less than .05%. The absorption of ZrO2 is excessive at 5.3. All AR designs passed the scotch tape adhesion test. The index of SrF2 in thin film form is lower than the bulk value. In half-wave coatings of SrF2 an index as low as 1.22 was observed. Bandwidths of three AR designs were 0.5 microns or greater. Absorptions of half-wave coatings at 1.06 and 3.8 microns indicate that further development will be required for these wavelengths. Absorption measurements for the PbF2/ThF4 design for CaF2 windows coated on both sides are reported for 5.3, 3.8, and 2.8 microns. The windows absorbed 0.04%, 0.2%, and 0.5%, respectively. Some designs were plaqued with stress induced birefringence in the visible which did not adversely affect the transmission in the IR. The PbF2, ThF4, and ZrO2 coatings did not show residual strain. The absorption measurements obtained on three different calorimeters are compared.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1976
- Accession Number
- ADA033103
Entities
People
- Melvin C. Ohmer
Organizations
- Air Force Research Laboratory