Spectral Shift Effects
When changing the Angle of Incidence (AOI) in a Bandpass Filter from 0° to 15°, several key effects occur:
Spectral Shift Effects
The most significant change is the blue shift phenomenon, where the transmission spectrum shifts toward shorter wavelengths as the AOI increases. For collimated light at angles up to 15 degrees, this shift can be predicted using the formula:
where λ_θ is the shifted wavelength and λ_o is the original wavelength.
Polarization Effects
As the AOI increases, the light beam experiences:- Separation into distinct s-polarized and p-polarized components
- Formation of a characteristic "hitch" around the 50% transmission point
- Reduced transmission efficiency compared to normal incidence
Bandwidth Changes
The filter's passband experiences two main changes:- The bandwidth becomes wider
- The center wavelength transmission efficiency remains relatively good up to about 20°
Performance Limitations
For standard bandpass filters:- The filter maintains effective transmission of the center wavelength (CWL) up to approximately 15° AOI
- This corresponds roughly to an f/1.9 system or a 30° full cone angle
- Beyond 20°, the effects become more severe and may prevent proper transmission