Can metals be transparent at certain wavelengths? My first reaction is No Way! It’s a myth, sort of like the transparent aluminum which is mentioned in the Star Trek whale movie. But then … reading the book Solid State Physics by J. S. Blakemore (2nd revised edition of 1985, published by Cambridge), I noticed in the table on page 24, under the list of properties of solids with various bonding types, the entry for metallic bonding type, this: “opaque and highly reflective in infrared and visible light; transparent in U.V.”. The three example materials listed for that row of the table are Sodium, Silver, and Nickel. So I have to suppose there must be some frequencies at least, at which at least one of those metals is transparent.
Now I’m really curious. A preliminary search for “transparent silver ultraviolet” turns up an article, at the URL http://www.telfor.rs/telfor2004/radovi/PEL-9-9.PDF which describes silver-dielectric crystals which allow some wavelengths through. An example application of such frequency-dependent transparency or opacity is a material which might be used as a microwave oven window, which would be transparent to visible light but opaque to microwaves. OK. My horizons have just expanded. A new concept, and some application possibilities.
Consider, for instance, what might be done with solar cells. Capture long wavelength radiation (greenhouse effect in micro) in an enclosure, achieve high temperature, and black body distribution provides shorter wavelength photons to kick photoelectrons off a material. Thermoelectric applications too. This is really neat! Got to do some reading.
I still don’t know about transparent pure metals, whether silver or aluminum or whatever. But at least it’s not an automatic dismissal of the concept anymore.
Best wishes,
Ken Roberts
20-Apr-2014
Logic, Astronomy, Science, and Ideas Too 