Wedge-filter spectrometer

• US 4,957,371 A
• Filed: 12/11/1987
• Issued: 09/18/1990
• Est. Priority Date: 12/11/1987
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Santa Barbara Research Center (Rtx Corporation)
• Inventors: Mika, Aram M., Pellicori, Samuel F.
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US07/132,227
• Time in Patent Office: 1,012 Days
• Field of Search: 356/416, 356/419, 350/166, 250/226
• US Class Current: 356/419
• CPC Class Codes: G01J 2003/1234 Continuously variable IF [CVIF]; Wedge type
• CPC Class Codes: G01J 3/12 Generating the spectrum; Monochromators
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G02B 5/288 comprising at least one thin film resonant cavity, e.g. in bandpass filters

Abstract

A wedge-filter spectrometer 1 comprises means 10 for spectrally dispersing an incident radiation beam comprising a first plurality of layers of high (H) index of refraction material and a second plurality of layers of low (L) index of refraction material, individual ones of the H and the L layers overlying one another in accordance with a given sequence, each of the H and the L layers having a substantially linearly tapered thickness of substantially constant slope, and means for detecting 17 at a plurality of points a spectrally dispersed radiation beam, the radiation beam being spectrally dispersed by the H and the L layers.

Claims

1. A wedge-filter spectrometer comprising:

means for spectrally dispersing an incident radiation beam, said dispersing means comprising a first plurality of layers of high (H) index of refraction material and a second plurality of layers of low (L) index of refraction material, individual ones of said H and said L layers overlying one another in a given sequence

space="preserve" listing-type="equation">H LL HLHLHL HH LHLHLH LL HL

each of said H and said L layers having a substantially linearly tapered thickness of substantially constant slope, said layers HH being a spacer layer having a predetermined thickness for defining a passband, the thickness being substantially equal to a length associated with a number of whole wavelengths that evenly fit within the thickness of said spacer layer; and

means, optically coupled to said dispersing means, for detecting at a plurality of points within a two-dimensional area a spectrally dispersed radiation beam, the radiation beam being spectrally dispersed by said H and said L layers.

2. A spectrometer as defined in claim 1 wherein said layers isolate a radiation transmission passband having a wavelength (λ

) given by

space="preserve" listing-type="equation">λ

=4nt

wherein n is the value of either the H or the L refractive index of the layers, and

wherein t is the total thickness of the layer of corresponding refractive index at a given point along said dispersing means from a reference point.

3. A wedge-filter spectrometer comprising:

means for spectrally dispersing an incident radiation beam, said dispersing means comprising a first plurality of layers of high (H) index of refraction material and a second plurality of layers of low (L) index of refraction material, individual ones of said H and said L layers overlying one another in a given sequence, each of said H and said L layers having a substantially linearly tapered thickness of substantially constant slope;

means, optically coupled to said dispersing means, for detecting at a plurality of points within a two-dimensional area a spectrally dispersed radiation beam, the radiation beam being spectrally dispersed by said H and said L layers; and

at least one interference blocking stack interposed between said incident radiation beam and an upper one of said layers.

4. A spectrometer as defined in claim 3 wherein said detecting means comprises a two dimensional array of photodiodes disposed to detect said dispersed radiation beam at a plurality of points.

5. A spectrometer as defined in claim 3 wherein said dispersing means is integrally formed upon a radiation receiving surface of said detecting means.

9. A spectrometer as defined in claim 3 wherein said plurality of interference layers comprise a plurality of said resonant cavity structures disposed one upon another for decreasing the width of said passband.

10. A spectrometer as defined in claim 9 wherein said spectrometer is responsive to radiation within a range of wavelengths of approximately 400 nm to 1000 nm and wherein said spectrometer further comprises a plurality of interference blocking stacks disposed upon said first surface of said substrate, each of said stacks being responsive to a given range of wavelengths for rejecting said given range of wavelengths.

11. A spectrometer as defined in claim 10 wherein said plurality of interference blocking stacks comprise three interference blocking stacks disposed adjacent one another upon said first surface, said stacks being disposed from said first edge to said second edge.

12. A spectrometer as defined in claim 11 wherein

a first one of said stacks is comprised of a plurality of substantially constant thickness layers of H and L material given by

[LH]⁶ 1.3[LH]⁶, where L and H are quarter waves at approximately λ

=520 nm;

a second one of said stacks is comprised of linearly tapered layers of H and L material given by

[LH]⁷ 2 [LH]⁷, where L and H are quarter waves at approximately λ

=420 nm; and

a third one of said stacks is comprised of substantially constant thickness layers of H and L material given by

[LH]⁶ 1.6 [LH]⁶, where L and H are quarter waves at approximately λ

=250 nm.

15. A spectrometer as defined in claim 12 wherein said cone of radiation is incident upon said first surface at an angle of between approximately 10°

to 20°

from a normal to said said first surface.

6. A wedge-filter spectrometer comprising:

a substrate comprised of a material which is substantially transparent to a cone of radiation incident upon a first surface of said substrate,

a plurality of linearly tapered interference layers disposed upon a second opposite surface of said substrate, said layers being disposed one upon another in a stacked fashion, each of said layers having a widest thickness along a first edge of said substrate and a narrowest thickness disposed along a second, opposite edge of said substrate, certain ones of said plurality of layers being comprised of a material having a high (H) index of refraction and certain ones of said plurality of layers being comprised of a material having a low (L) index of refraction, said H and L layers being arranged one upon another in accordance with a predetermined sequence for spectrally dispersing the incident radiation;

a two dimensional array of radiation detectors being disposed substantially parallel to said first surface of said substrate and underlying said plurality of layers, said array being responsive to said spectrally dispersed radiation at a plurality of points therein; and

means for maintaining said array of detectors in a parallel orientation with said upper surface.

7. A spectrometer as defined in claim 6 wherein said predetermined sequence defines a resonant cavity structure for producing a wavelength passband centered at a wavelength of λ

_c where

λ

_c is the passband center wavelength, and

λ

₀ is a reference wavelength given by

λ

₀ =4n_H t_H =4n_L t_L

wherein

n_H is the index of refraction of said H material,

t_H is the thickness of said H material,

n_L is the index of refraction of said L material, and

t_L is the thickness of said L material.

8. A spectrometer as defined in claim 7 wherein said predetermined format is defined by layers

13. A spectrometer as defined in claim 6 where said substrate is comprised of optical glass and wherein said L material is comprised of silicon dioxide and wherein said H material is comprised of titanium dioxide.

14. A spectrometer as defined in claim 6 wherein said maintaining means is a tapered layer of optical cement.

16. A spectrometer as defined in claim 6 wherein said spectrometer is responsive to radiation within a range of wavelengths of approximately 400 nm to 1000 nm and wherein said spectrometer further comprises a plurality of interference blocking stacks disposed upon said first surface of said substrate, each of said stacks being responsive to a given range of wavelengths.

17. A spectrometer as defined in claim 16 wherein said plurality of interference blocking stacks comprise three interference blocking stacks disposed adjacent one another upon said first surface, said stacks being disposed from said first edge to said second edge.

18. A wedge-filter spectrometer comprising:

means for spectrally dispersing radiation incident upon a first surface of said dispersing means, said dispersing means comprising a first plurality of layers of high (H) index of refraction material and a second plurality of layers of low (L) index of refraction material, individual ones of said H and said L layers overlying one another in a predetermined sequence, each of said H and said L layers having a substantially linearly tapered thickness of substantially constant slope, the predetermined sequence including a sequence having a plurality of centrally disposed layers having the same index of refraction, a plurality of pairs of layers comprised of a layer of high index of refraction material, a first one of the plurality of pairs of layers being disposed adjacent to a top surface of said centrally disposed layers, a second one of the plurality of pairs of layers being disposed adjacent to a bottom surface of said centrally disposed layers, and a pair of layers each having the same index of refraction disposed adjacent to each of the plurality of pair of layers; and

means, optically coupled to said dispersing means at a second surface opposite the first surface, for detecting with a two-dimensional array of radiation sensors the spectrally dispersed radiation.

19. A wedge-filter spectrometer as defined in claim 18 wherein said detecting means is selected from a group consisting of a solid-state two-dimensional detector array, a vidicon, a photomultiplier with microchannel plates and a CCD imaging device.

20. A wedge-filter spectrometer as defined in claim 18 wherein said dispersing means is disposed upon a radiation receiving surface of said detecting means.

21. A wedge-filter spectrometer comprising:

means for spectrally dispersing radiation incident upon a first surface of said dispersing means, said dispersing means comprising a first plurality of layers of high (H) index of refraction material and a second plurality of layers of low (L) index of refraction material, individual ones of said H and said L layers overlying one another in a predetermined sequence, each of said H and said L layers having a substantially linearly tapered thickness of substantially constant slope;

means, optically coupled to said dispersing means at a second surface opposite the first surface, for detecting with a two-dimensional array of radiation sensors the spectrally dispersed radiation; and

at least one interference blocking stack interposed between said first surface of said dispersing means and the radiation.