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Difficult optical metallic surface

2004

I'm a research assistant working on a new type of particle detector. The design requires an array of small hexagonal metal rods approx. 7 mm in diameter and 30 cm long. Each of the rods needs to have a high-quality optically reflective surface on each of the 6 long sides. All surfaces must be metallic.

1) What metals should we use? Density of the metal is a factor, the denser, the better. Right now one idea is to have a tungsten inner rod, covered with nickel (easily polished), with a thin aluminized layer over that (reflectivity), topped by a very thin gold layer (stop oxidization). Other suggestions?

2) How should we get a good optical surface? The strange shape makes conventional mechanical polishing very difficult. We've experimented with ion-beam polishing, and are currently looking at electropolishing. Are there any other processes that would be worth looking into?

Sam Ose
Physics research - Ames, Iowa, USA

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2004

Just a thought, Have you considered silver as a reflective coating ? It's highly reflective over the visible light range - more so than aluminium. I don't know whether it would be best to deposit a dull silver (with no organics) and polish or whether a fully bright silver would be better. Only testing would tell, unless somebody else has already done the tests, NASA perhaps examining specular reflectance of metals for mirrors ?

Regards,

Richard Guise
- Lowestoft, U.K.

I would also suggest a silver coating, if corrosion is a problem covered with a Rhodium-coating , which should give a good resistance and optical reflection.

Marcus Hahn
- Lucerne, Switzerland
2004