Hi,
I would like to know is it possible to have a Band pass Interfernce filter with following specifications:
Centre Wavelenght: 1064 +/- 2nm
Peake Transmission: >90%
FW at 50% of peak transmission: 35nm
FOV: +/-15degree
Dia: 40mm
all other wavelengths must be suppressed
The specification I am concerned here is Peak Transmission >90%....Is it possible to achieve this much high peak transmission in interference filter beacause all commericially available filters have only upto 60%.
A peak transmission of 90% is hard to get with a mononchromator but as I know impossible with interference filters. So 60% is the best you can expect.
Interference filter is basically to enhance the transmittence. If there are 2 surfaces then the minimum reflection from each surface will be 4% leading to minimum transmittance of around 93% without any coating. But if we do AR coatings (as we do in interference filters) the transmittance must increase???...So why not >90%????
Usually the peak transmittance is compromised by the desire for wider acceptance angles or broader passbands, as well as good old fashioned production engineering. If you can live with a narrow angle and passband there are so-called 'laser-line' filters with transmittance of over 90% at the relevant wavelength. 40 mm diamter may well be a special order item though. Edmund Optics have them (edmundoptics.com), as do other optics houses.
If you want better performance than that, you can always use an etalon - if you can live with the narrow angle of view.
One can get interference filters up to 50mm square - easily. For +/- 2NM in the IR-A band, the filter would probably require precise temperature control which would increase the cost dramatically. Try http://www.daystarfilters.com/ they may be able to help you with a custom job.
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