Interference filter for non-zero angle of incidence spectroscopy
The present disclosure relates to thin film optical interference filters. The filters include a substrate and a plurality of alternating material layers deposited on the substrate. When operated at about 45° angle of incidence, the filters exhibit at least one of improved polarization splitting, edge steepness, bandpass bandwidth, and blocking, relative to conventional thin film interference filters.
1. An interference filter, comprising:
a substrate, and
a plurality of alternating first and second material layers deposited on said substrate, said material layers having respectively different refractive indices;
wherein said plurality of alternating first and second material layers are configured such that when light from a light source impinges on said filter at an Angle of incidence of about 45°, said filter defines a spectrum for light of average polarization, said spectrum comprising a first stopband region and a second stopband region separated by a passband region having a passband bandwidth;
wherein said first stopband region corresponds to a fundamental stopband;
wherein said second stopband region comprises a long wave edge and a short wave edge, and encompasses a range of wavelengths other than wavelengths corresponding to a harmonic of the first stopband region; and
wherein at least one of said long wave edge and said short wave edge has an edge steepness, when measured between 10-90% transmission, of about 0.75% or less, relative to an edge wavelength of said second stopband region.
2. The interference filter of claim 1 , wherein at least one of said long wave edge and short wave edge exhibits an edge steepness, when measured from optical density 3 to 90% transmission, of about 0.50% or less.
3. The interference filter of claim 1 , wherein at least one of said long wave edge and short wave edge exhibits an edge steepness, when measured from optical density 1 to 90% transmission, of about 0.25% or less.