Compact birefringent spectrometer

• US 6,618,142 B1
• Filed: 06/26/2001
• Issued: 09/09/2003
• Est. Priority Date: 06/26/2001
• Status: Expired due to Fees

• Current Assignee: The Government Of The United States As Represented By The Secretary Of The Navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Roberts, Mark W.
• Primary Examiner(s): Nguyen, Thong
• Assistant Examiner(s): Lavarias, Arnel C.
• Application Number:
  US09/891,704
• Time in Patent Office: 805 Days
• Field of Search: 356/326, 356/300, 356/327, 356/331, 356/332, 359/350, 359/352, 359/487, 359/488, 359/494, 359/495, 359/496, 359/497, 359/498, 359/500, 359/615, 359/831, 359/837, 385/36, 362/19, 362/26, 362/31
• US Class Current: 356/327
• CPC Class Codes: G01J 3/0256 Compact construction
• CPC Class Codes: G01J 3/0259 Monolithic
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51

Abstract

A spectrometer uses collimated, P-polarized light made incident on a surface of an optically transparent material at angle θ_INC. The material transmits the light which reaches a boundary surface between the input material and an output optically transparent material. The input material is preferably highly dispersive, making Snell component values at the boundary surface markedly different for different wavelengths. The output material is preferably of low dispersion and high birefringence. Only one wavelength at the boundary surface has a Snell component value tangent to its corresponding index surface in the output section. Within this section, the ray vector for this wavelength is parallel to the boundary surface. Because optical energy propagates in the ray vector direction, only the narrow range of wavelengths having ray vectors substantially parallel to the boundary surface reach an output surface of the device. This narrow range of wavelengths comprises the passband incident on a detector.

Claims

1. A spectrometer for discerning components of collimated light comprising:

a P-polarizer for P-polarizing said collimated light;

an input optically transparent element having an input surface for receiving said P-polarized light and for transmitting said P-polarized light to a boundary surface of said input element, said input element being of a material that is of relatively high light dispersiveness that separates said P-polarized light into wavelength dependent (k-vector) directions representative of different colors, said input element being aligned with respect to said boundary surface to a maximize the dispersive effect of said material so that Snell component values at said boundary surface are made markedly different for different wavelengths of said P-polarized light; and

an output optically transparent element for receiving said P-polarized light as transmitted through said input element and presented at said boundary surface and having an output surface for emitting light within a desired passband when present, said output element being of a highly birefringent, relatively low light dispersiveness material having an optic axis other than normal to said boundary surface and aligned to maximize the birefringence effect of said material, said material being characterized by having a plurality of index surfaces corresponding to different colors so that a Snell'"'"'s component received from said input element within said passband aligns tangentially with one of said index surfaces to propagate light within said desired passband through said outer surface in the direction of a ray vector that is substantially parallel to said boundary surface.

2. The spectrometer of claim 1 wherein said P-polarized light is incident on said input surface at an angle of incidence and wherein frequencies within said passband of said spectrometer are selected by adjusting said angle of incidence.

3. The spectrometer of claim 1 wherein said output element has an extension that extends past said input element to terminate with said output surface.

4. The spectrometer of claim 3 wherein the length of said extension is selected to adjust the width of said passband.

5. The spectrometer of claim 1 wherein said output surface is beveled to maximize transmission of light in said passband through said output surface.

6. The spectrometer of claim 1 further including a detector for detecting the presence and intensity of light emitted at said output surface.

7. The spectrometer of claim 1 wherein said output optically transparent element is used for ultraviolet through visible light and wherein said output element is of a material chosen from the group of calcite, LiNbO₃, and LiIO₃.

8. The spectrometer of claim 1 wherein said output optically transparent element is used for infrared light and wherein said element is of a material chosen from the group of Selenium and TiO₂.

9. The spectrometer of claim 1 wherein said input optically transparent element is used for ultraviolet light and wherein said input element is of a material chosen from the group of KBr, KCl, and KI.

10. The spectrometer of claim 1 wherein said input optically transparent element is used for near-ultraviolet through infrared light and wherein said input element is of a material chosen from the group of sapphire, MgO, CsBr and BaF₂.

11. The spectrometer of claim 1 wherein said input optically transparent element is used for visible light and wherein said input element is of a material chosen from the group of sphene and flint glass.

12. The spectrometer of claim 1 wherein said input optically transparent element is used visible through infrared light and wherein said input element is of a ZnSe.

13. The spectrometer of claim 1 wherein said input optically transparent element is used for infrared light and wherein said input element is of a material chosen from the group of NaCl, NaF and GaAs.

14. The spectrometer of claim 1 wherein said output optically transparent element is chosen of a material exhibiting dispersion of the bisectrices.