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Almost everyone who attends the SPIE DSS Exposition and many other optical and optical engineering Conferences & Expos has received a gold-plated paper clip from Mr. David Epner, personally.
Well, the gold costing that Epner supplies to the optics industry has some interesting infrared reflectance (and emittance) properties.
Those properties, specifically the hemispherical spectral reflectance in the near, mid and far infrared is now available for all to view first hand on the Epner website.
A copy of the curve and the data related to it can be downloaded from the site, too.
Shown here, of course, is the Spectral Reflectance of "Laser Gold", which as most know is the complement of Spectral Emittance at each and every wavelength from the formula: e(lambda) = 1 - r(lambda) - t(lambda),
where, respectively:
e is the emittance,
r is the reflectance,
t is the transmittance and
lambda is the wavelength (on this graph shown in units of micrometers). (Note: the usual expressions for these terms are in the Greek letters, epsilon, rho, tau and lambda and have been modified for use on this webpage)
The assumption most often made is that the transmittance of solid gold is zero, or so nearly so that it can be neglected.
That can be an false assumption in some cases according to the degree of precision required in a specific measurement situation. For instance, a very thin film of gold may be partially transparent especially in the long wavelength regions of the infrared and the optical properties on the material under the gold layer may come into play.
