[QUOTE=Laser Ben;94740]Odd, I did not know that optics could have a soft coating. What is the difference in how the coating is applied?
Once upon a time, ebeam or ion blasting or magnetron sputtering a crucible of hard material did not exist, so only thermal evaporation out of hot moly or tungsten boats was used, a lot of the low melting point materials that had the right high refractive indexes were were salts that dissolve in water.
modern stuff like tio2 and sio2 are hard, and are often melted with 2-3 amps of e- beam aimed into a conductive graphite crucible that looks strangely exactly like a thimble. I've used e- beam a few times, and its so much easier to get a uniform coating, compared to thermal evap. Also the density of the final product is higher. Hard coated materials will often not melt in the clowing tungsten boats.
The only reason to use a soft coat today is Far IR (rare) or quick prototypes of complex designs. Or perhaps running a coating in your basement or a poorly equipped second rate university lab. One last excuse might be deliberately making one layer so you can float a film off a substrate in mems applications. Many lab bandpass filters are still soft, you can spot them a mile a away because they have glass on both optical faces and are potted in a black bakelite like material to keep the water out. They have extreme blocking range , from UV to Xray to far IR, but short lifetime,
Hint for spotting the soft coats, they often have metallic silver Spacer layers in between the quarter wave layers, and this is a bluish metallic reflective layer that looks like the metallic dust in various car paint jobs.
Steve
Last edited by mixedgas; 05-05-2009 at 17:27.
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Originally Posted by mattrg02
His 'stated' wavelength was also way off! 
