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Calculation of Central Wavelength

When interference filters are used at angles other than normal incidence, the optical path difference between the direct transmitted beam and the multiple order reflections within the cavity decreases, causing a corresponding decrease in the wavelength of peak transmission. Changes in the bandwidth and transmission characteristics are generally small (for the relatively wide passbands used here).

For angular tilts of less than 30 tex2html_wrap_inline5509 , the central wavelength can be calculated from the expression


where tex2html_wrap_inline6449 = Central wavelength at normal incidence

tex2html_wrap_inline6451 = Central wavelength at the off-normal angle, tex2html_wrap_inline6453

and n = Effective refractive index of the total filter.

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Wed Sep 17 12:36:20 BST 1997