UV-Shifted Durable Silver Coating for Astronomical Mirrors
Conference
·
OSTI ID:792715
- LLNL
Silver has the highest reflectance of all of the metals, but it tarnishes in the presence of sulfides, chlorides, and oxides in the atmosphere. Also, the silver reflectance is very low at wavelengths below 400 nm making aluminum more desirable mirror coating for the UV region. They have found a way to prevent silver tarnishing by sandwiching the silver layer between two thin layers of NiCrN{sub x}, and to extend the metal's high reflectance down to 200 nm by depositing the (thin) Ag layer on top of Al. Thus, the uv is transmitted through the thin Ag layer below 400 nm wavelength, and is reflected from the Al layer underneath. This UV-shifted durable coating provides a valuable alternative to the aluminum coating for telescope mirror coatings where high throughput and durability are important considerations. The throughput for a telescope with, say, six reflections from silver coatings is (0.97){sup 6} = 83% compared to (0.92){sup 6} = 60% for aluminum coatings, or 28% less. The use of silver coatings allows more photons to be collected by primary mirror. Aluminum also has a reflectance dip at 850 nm caused by inter-band transitions which is eliminated by placing the thin Ag layer on top. This paper describes a non-tarnishing silver coating having high reflectance down into the UV region. The average specular reflectance is 70%-97% in the near-UV, 95%-99% in the visible region, and {ge} 99% in the infrared region covering the total wavelength range 200 nm to 10,000 nm. Figure 1 compares the reflectance of the UVHR-LLNL silver coating to bare silver and aluminum over-coated with magnesium fluoride over the wavelength range 300 nm to 2000 nm.
- Research Organization:
- Lawrence Livermore National Lab., CA (US)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 792715
- Report Number(s):
- UCRL-JC-136508
- Country of Publication:
- United States
- Language:
- English
Similar Records
High Reflectivity of Silver Extended Down to 200 NM
Durable silver mirror with ultra-violet thru far infra-red reflection
Prevention of corrosion of silver reflectors for the National Ignition Facility
Conference
·
Mon Jun 04 00:00:00 EDT 2001
·
OSTI ID:15005391
Durable silver mirror with ultra-violet thru far infra-red reflection
Patent
·
Mon Nov 22 23:00:00 EST 2010
·
OSTI ID:1014761
Prevention of corrosion of silver reflectors for the National Ignition Facility
Conference
·
Thu Jul 01 00:00:00 EDT 1999
·
OSTI ID:14597