|MadSci Network: Physics|
Hello, Chao. Well, I'm not sure I can give you exactly what you want, but I'll do my best. The only way I can think of to get broad bandwidth, circularly-polarized light is to do exactly what you mentioned in your post: a polarizer followed by a quarter waveplate. You can get very broad bandwidth polarizers using a variety of methods, but obtaining a broad bandwidth quarter waveplate is harder. However, they're out there. You can do a web search on "achromatic waveplates" and find several vendors who provide such an optical element. For example, one vendor (I feel I should strive for objectivity, and refrain from endorsing a particular company) quotes a quarter waveplate that will work from 465-610 nm, with less than a 1/100 wave deviation from 1/4 wave over that whole bandwidth. Another company quotes a similar element, without the tolerance specification, that they say works over the 400-700 nm band (though I suspect that it's performance is identical to the first company's product). Since this covers almost the whole visible spectrum, I imagine it would be suitable for what you have in mind. These things aren't cheap, generally costing hundreds of dollars US. Unfortunately, I cannot think of an affordable way to come up with anything similar. The commercial products are based on the combination of two specially-tailored, specially-packaged optical flats. There's simply no way to duplicate that without going through a similarly-complicated effort. Sorry I couldn't come up with better, but if I come across anything in the near future I'll try to let you know. - Guy
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