| Author | Message | ||
     Edward Chidley |
Thanks for all your earlier suggestions - I can't find our earlier discussion. Hvaing had time to consider them, I have revised what I need. Does anybody have further suggestions ? Interference filters can be designed not to transmit light over the required waveband, for one (or a small range of) angle of incidence; the requirement is for a truly absorbing material, that blocks/transmits over all angles, and does not reflect too much. The substance is required to highly absorbing between approximately 1000 - 3000 nm. (Schott KG series meets this spec., but not the following..)And it needs to have a high degree of transparency between about 3000 nm and 12000 nm and to be moderately transparent in the visible part of the EM spectrum - it's allowed to have absorbtion bands there, or be less transparent though. Of course this will all depend on thickness, but I mean by 'largely absorbing' and 'high degree of transparency' the layer will transmit less than 10% and transmit 80%, i.e., the requirement is about relative transparency. However, a combination of materials which absorb anywhere between 1000 nm and 3000 nm is allowed, as long as they have low absorbtion beyond 3000 nm. Or the best approximation the specification. | ||
| hlmark |
Edward - since my previous message seems likely to have been among the ones that got lost, let me repeat it. The possibilities that I can think of are: 1) Use several stacked narrow-to-medium bandwidth interference filters with staggered center wavelengths. Then if a ray of some wavelength comes in at an angle so that it's "regular" filter doesn't take it out, it will be at a wavelength where a different one will, at that angle. 2) Work with the Schott people to design an absorbing filter based on sapphire rather than glass; sapphire will transmit in the IR (at least to 5500 nm). This will probably be expensive, since it is an R&D project all in itself, and probably a difficult one since sapphire requires special techniques to work with. You might have to bring in a sapphire manufacturer as well as the Schott people who can recommend the additives to give the absorbance characteristics you want. If neither of those solutions are satisfactory, I think you might be out of luck. I don't know of any material (except diamond, and the various salts that are commonly used for mid-IR optics) that is transparent over the wavelength range you specify. Come to think of it, maybe you can dope a salt with something that will absorb in your desired region - ask Schott for some recommendations for what to try. There are some salts that are not soluble in water (BaF2, for example) and there are many compendia of optical and other properties of the various salts in the mid-IR literature. But it's still an R&D project and therefore will be relatively expensive. Howard \o/ /_\ | ||
| Tony Davies (Td) |
Dear Edward, Howard and all contributors, On the left of your screen there are three headings: Discussion, Documentation, and Utilities. In Utilities there is a Keyword search I just entered "filter" and the first hit was Absorbing Materials between 1um and 3um; 2nd June 2005!!!!!!! Nothing is lost from this site; it is now a very useful treasury of advice and knowledge. If you think you have a new question; it is worth asking the "oracle" first. When you do have a new question; please start a new thread and NOT just attach it to a current discussion. Best wishes, Tony |