Beamsplitter Configuration For Optical Subtraction of Self Emission with Fourier Transform Spectrometer in Dual Input Port Mode

• US 20120194822A1
• Filed: 01/30/2012
• Published: 08/02/2012
• Est. Priority Date: 02/01/2011
• Status: Active Grant

• Current Assignee: ABB Incorporated (ABB Limited)
• Original Assignee: Abb Bomem, Inc. (ABB Limited)
• Inventors: Buijs, Henry L.
• Granted Patent: US 9,146,158 B2
• Time in Patent Office: Days
• US Class Current: 356/451
• CPC Class Codes: G01J 3/0205 Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
• CPC Class Codes: G01J 3/453 by correlation of the amplitudes
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0047 for use with a light source G02B19/009, G02B19/0095 take precedence; details of lighting devices in general F21V; non-semiconductor lasers having optical devices external to the laser cavity H01S3/005
• CPC Class Codes: G02B 19/009 for use with infrared radiation
• CPC Class Codes: G02B 27/106 for splitting or combining a plurality of identical beams or images, e.g. image replication

Abstract

A four port scanning Michelson interferometer suppresses self-emission by using either a beamsplitter that is uncoated or a beamsplitter that has reflection enhancing dielectric coatings in the splitting and combining areas of the substrate on opposite sides of the substrate. Both beamsplitters are fabricated from infrared optical materials that have a predetermined absorptivity in a predetermined wavelength interval which is from 2 μm (5000 cm⁻¹) to 13 μm (770 cm⁻¹) in the infrared. The optical materials of the uncoated beamsplitter are selected from a group of materials made up of ZnSe, ZnS, CdS, CdTe, Silicon, Germanium or Diamond. The optical materials of the other beamsplitter are selected from a group of materials made up of KBr, KCl, NaCl, CsI, BaF, CaF and the like.

Claims

1. A four port Michelson interferometer comprising:

a first input port viewing a first field of view and a second input port viewing a second field of view; and

a single substrate beamsplitter fabricated from infrared optical materials that have a predetermined absorptivity in a predetermined wavelength interval, said beamsplitter having a self-emission arising from said predetermined absorptivity;

said Michelson interferometer performing a direct optical subtractive comparison of said second field of view against said first field of view to provide a difference in spectra and optical subtraction of said self-emission of said single substrate beamsplitter from said difference in spectra to suppress said self-emission.

2. The interferometer of claim 1 where wherein said single substrate beamsplitter is an uncoated substrate.

3. The interferometer of claim 2 wherein said single uncoated substrate beamsplitter is fabricated from a material selected from a group of infrared optical materials consisting of ZnSe, ZnS, CdS, CdTe, Silicon, Germanium or Diamond.

4. The interferometer of claim 1 wherein said predetermined wavelength interval is from 2 μ

m (5000 cm<sup>−

1</sup>) to 13 μ

m (770 cm<sup>−

1</sup>) in the infrared.

5. The interferometer of claim 1 wherein said single substrate beamsplitter comprises opposing sides one of which is a splitting area and the other of which is a combining area and reflection enhancing dielectric coatings on said splitting and combining areas.

6. The interferometer of claim 5 wherein said single substrate beamsplitter is fabricated from a low index of refraction infrared transparent material.

7. The interferometer of claim 6 wherein said low index of refraction infrared transparent material is selected from a group of infrared optical materials consisting of KBr, KCl, NaCl, CsI, BaF, CaF.

8. The interferometer of claim 1 wherein said single substrate beamsplitter comprises:

opposing first and second sides, one half of said first side of said substrate is a splitting area and one half of said second side of said substrate is a combining area, and

reflection enhancing dielectric coatings on said splitting and combining areas.

9. The interferometer of claim 8 wherein the other half of each of said first and said second sides are provided with anti-reflection coatings.

10. The interferometer of claim 1 wherein said interferometer is suitable for a spectro-radiometer system used for remote quantitative determination of surface emitted radiance.

11. The interferometer of claim 1 wherein said interferometer is suitable for a spectro-radiometer system used for remote quantitative determination of radiance emitted from a gas sample.

12. The interferometer of claim 11 wherein said gas sample is air.

13. The interferometer of claim 10 wherein said interferometer has two retro-reflector assemblies positioned such that a splitting of an input light beam occurs on one side of said single substrate beamsplitter and a subsequent combining of said split beam occurs on an opposite side of said substrate.

14. A spectro-radiometer system comprising:

a. a four port Michelson interferometer comprising;

a first input port viewing a first field of view and a second input port viewing a second field of view; and

a single substrate beamsplitter fabricated from infrared optical materials that have a predetermined absorptivity in a predetermined wavelength interval, said beamsplitter having a self-emission arising from said predetermined absorptivity; and

b. two retro-reflector assemblies positioned such that a splitting of an input light beam occurs on one side of said single substrate beamsplitter and a subsequent combining of said split beam occurs on an opposite side of said substrate;

said Michelson interferometer performing a direct optical subtractive comparison of said second field of view against said first field of view to provide a difference in spectra and optical subtraction of said self-emission of said single substrate beamsplitter from said difference in spectra to suppress said self-emission.

15. The interferometer of claim 14 where wherein said single substrate beamsplitter is an uncoated substrate.

16. The interferometer of claim 15 wherein said single uncoated substrate beamsplitter is fabricated from a material selected from a group of infrared optical materials consisting of ZnSe, ZnS, CdS, CdTe, Silicon, Germanium or Diamond.

17. The interferometer of claim 14 wherein said predetermined wavelength interval is from 2 μ

m (5000 cm<sup>−

1</sup>) to 13 μ

m (770 cm<sup>−

1</sup>) in the infrared.