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 for non-zero-angle of incidence spectroscopy, 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 s-polarized light and a spectrum for p-polarized light, each spectrum comprising a first stopband region and a second stopband region separated by a passband region having a passband bandwidth of at least about 25% of an edge wavelength for light of average polarization corresponding to the second stopband region; and
said filter exhibits polarization splitting of about ≦0.5%, relative to said edge wavelength;
wherein said first stopband region is associated with a fundamental stopband, and said second stopband region is associated with at least one of: a harmonic stopband of the fundamental stopband and a non-harmonic stopband of the fundamental stopband.
2. The interference filter of claim 1 , wherein said passband bandwidth of at least about 25% of said edge wavelength is a passband bandwidth of at least about 50% of the edge wavelength.
3. The interference filter of claim 1 , wherein said passband bandwidth of at least about 25% of said edge wavelength is a passband bandwidth of at least about 58% of the edge wavelength.
4. The interference filter of claim 1 , wherein said polarization splitting is ≦0.25%, relative to said edge wavelength.
5. The interference filter of claim 1 , wherein said second stopband region is associated with the non-harmonic stopband of said fundamental stopband.
6. The interference filter of claim 1 , wherein said second stopband region corresponds to a passband defect.
7. The interference filter of claim 1 , wherein said first stopband region and said second stopband region are present in distinct wavelength ranges within the 425 nm to about 1250 nm region of the electromagnetic spectrum.
8. The interference filter of claim 1 , wherein said second stopband region transmits≦10% of light having a wavelength within the second stopband region.
9. The interference filter of claim 8 , wherein said second stopband region transmits substantially 0% of light having a wavelength within the second stopband region.
10. The interference filter of claim 8 , wherein said second stopband region is associated with a non-harmonic stopband of said fundamental stopband.
11. The interference filter of claim 8 , wherein said light having a wavelength within said second stopband region originates from said light source, said light source configured to provide substantially monochromatic light having a wavelength λ L , wherein λ L is chosen from 532.0 nm and 785.0 nm.
12. A spectroscopy system, comprising:
an input light source capable of providing excitation light having at least a wavelength in an excitation band of a sample to be analyzed;
a dichroic beamsplitter optical filter configured to direct said excitation light onto said sample, and substantially transmit light scattered by said sample having a corresponding shift in wavelength; and
a detector for detecting light scattered by said sample;
wherein said dichroic beamsplitter optical filter comprises:
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 said input light source impinges on said dichroic beamsplitter optical filter at an Angle of incidence of about 45°, said dichroic beamsplitter optical filter defines a spectrum for s-polarized light and a spectrum for p-polarized light, each spectrum comprising a first stopband region and a second stopband region separated by a passband region of at least about 25% of an edge wavelength for light of average polarization corresponding to the second stopband region;
wherein said dichroic beamsplitter optical filter exhibits polarization splitting of less than about 0.5% relative to the edge wavelength; and
wherein said first stopband region is associated with a fundamental stopband, and said second stopband region is associated with at least one of: a harmonic stopband of the fundamental stopband and a non-harmonic stopband of the fundamental stopband.
13. The spectroscopy system of claim 12 , wherein said input light source provides substantially monochromatic light having a wavelength λ L , and said dichroic beamsplitter optical filter transmits less than 2% of said substantially monochromatic light.
14. The spectroscopy system of claim 13 , wherein λ L is chosen from 532.0 nm and 785.0 nm.
15. The spectroscopy system of claim 13 , wherein said dichroic beamsplitter optical filter blocks substantially 100% of said substantially monochromatic light.