Well, not really. There are a number of factors that must weighed before we start coating things. How much heat is your part going to take? Will it be exposed to high humidity? What wavelength range is the device being used over? The answer to each of these questions will determine the ideal coating for your device.**
There are a number of solutions to this problem. The traditional solution is to use a barium sulfate-based coating. The old war-horse is Eastman 6080, white reflectance coating, developed in the early 1970’s. There are a number of iterations of this coating out there (many of them developed by yours truly). Our version is called Avian-BTM white reflectance coating (the –B, cleverly enough, is for barium sulfate). This is a water/alcohol-based coating with barium sulfate and a binder. It adheres well to most metal and plastic surfaces (with a primer coat) and is both highly reflective and highly diffuse. The coating is also easily applied with a spray gun or even an air-brush for small parts. It is really the standard (and traditional) white reflectance coating. The coating is quite effective over a wide wavelength range (250- about 1300 nm, although it can be pushed out to about 2000 nm) and is 98+% reflective over a good bit of that range.
Now, suppose you have a system where you can’t use a coating. Maybe it’s a small part that you can’t get inside to spray the coating (these coatings all need to be applied in multiple- usually 15-20 coats) or the device will be seeing fairly high temperatures (say extended time at >100°C). What can you do? The solution is not a coating but a material, sintered PTFE, known variously as Spectralon™, Fluorilon™, and other trade names. They are all derived from work done by Vic Weidner at NIST in the early 1980’s but extended upon and patented by the author in the late 1980’s. We’ll cover sintered PTFE in the next blog offering. It’s a long and fascinating story…
** by devices, we mean integrating spheres, boxes, cavities, and any myriad of other optical components- baffles, port plugs, port frames, etc.
Summary Table of Diffuse White Materials Properties
|Name||Useful Wavelength Range||Useful Temperature Range||Water
|250nm – 2μm||-40°C to +90°C||Low||Yes|
(polyurethane and proprietary pigment)
|320nm – 1.25μm||-40°C to +100°C||Good||Yes|
|350nm-1.2μm||up to 80°C||High||No|