Encoder spectrograph for analyzing radiation using spatial modulation of radiation dispersed by wavelength

• US 7,262,846 B2
• Filed: 06/28/2005
• Issued: 08/28/2007
• Est. Priority Date: 06/28/2004
• Status: Expired due to Fees

• Current Assignee: Mudlogging Systems Inc. (ALS Oil & Gas)
• Original Assignee: Aspectrics
• Inventors: Hagler, Thomas W.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US11/169,824
• Publication Number:
  US 20050286049A1
• Time in Patent Office: 791 Days
• Field of Search: 356/305, 356/310, 356/326, 356/328, 356/330, 356/332, 356/334
• US Class Current: 356/330
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0202 Mechanical elements; Supports for optical elements
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/0291 Housings; Spectrometer accessories; Spatial arrangement of elements, e.g. folded path arrangements
• CPC Class Codes: G01J 3/0294 Multi-channel spectroscopy
• CPC Class Codes: G01J 3/18 using diffraction elements, e.g. grating gratings per se G02B
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/317 Special constructive features
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/552 Attenuated total reflection
• CPC Class Codes: G01N 2201/129 Using chemometrical methods

Abstract

An encoder spectrograph is used to analyze radiation from one or more samples in various configurations. The radiation is analyzed by spatially modulating the radiation after it has been dispersed by wavelength or imaged along a line. Dual encoder spectrographs may be used to encode radiation using a single modulator.

Claims

1. An encoder spectrograph for encoding and detecting one or more spectral components of a radiation beam, the encoder spectrograph comprising:

a concave diffraction grating that disperses a received incident beam of radiation by wavelength;

a crossover focusing reflector that redirects the dispersed beam across the incident beam to form an image dispersed by wavelength along a dispersion axis;

a spatial light modulator positioned to receive the dispersed image on a surface thereof, the spatial light modulator modulating the intensity of the dispersed image by a position along the dispersion axis to provide an encoded beam;

a crossover fast collection optic that collects the encoded beam from the spatial light modulator and redirects the encoded beam across the dispersed beam;

a detector lens that focuses the encoded beam to form a substantially overlapping image; and

a detector element positioned to receive the overlapping image and produce a signal representative of the encoded beam.

2. The encoder spectrograph of claim 1, wherein the concave diffraction grating, the crossover focusing reflector, the crossover fast collection optic, and the detector lens each have an optical center that is located in a substantially common plane.

3. The encoder spectrograph of claim 2, wherein the common plane is parallel to a perpendicular bisector of a midpoint of the dispersed image.

4. The encoder spectrograph of claim 1, wherein the concave diffraction grating, the crossover focusing reflector, the crossover fast collection optic, and the detector lens each have a vertex that is located in a substantially common plane.

5. The encoder spectrograph of claim 1, wherein the concave diffraction grating is mounted at an inclination angle so that the crossover focusing reflector just clears the incident beam.

6. The encoder spectrograph of claim 1, wherein the spatial light modulator reflects the dispersed image towards the crossover fast collection optic.

7. The encoder spectrograph of claim 1, wherein the received incident beam is substantially parallel to a detector axis normal to the detector element.

8. The encoder spectrograph of claim 1, wherein the received incident beam and a detector axis normal to the detector element are substantially parallel to the surface of the spatial light modulator.

9. The encoder spectrograph of claim 1, wherein the diffraction grating is mounted at an inclined auto-collimation angle so that the diffraction angles of the diffraction grating are symmetric about a midpoint of the dispersed beam.

10. The encoder spectrograph of claim 1, wherein the spatial light modulator comprises a rotating disc having a plurality of radiation filters located at different radii from a rotation axis, the radiation filters corresponding to positions along the dispersion axis.

11. The encoder spectrograph of claim 10, further comprising:

a motor for rotating the spatial light modulator about the rotation axis, the motor, the concave diffraction grating, the crossover focusing reflector, the crossover fast collection optic, and the detector lens located on the same side of the spatial light modulator.

12. The encoder spectrograph of claim 10, wherein the concave diffraction grating and the detector element are located on opposite sides of the rotation axis of the spatial light modulator.

13. The encoder spectrograph of claim 1, wherein the spatial light modulator comprises an addressable LCD.

14. The encoder spectrograph of claim 1, wherein the spatial light modulator comprises a MEMS device.

15. The encoder spectrograph of claim 1, wherein a portion of the detector lens is cut away to prevent mechanical interference with the incident beam.

16. The encoder spectrograph of claim 1, wherein a portion of the crossover fast collection optic is cut away to prevent mechanical interference with the dispersed beam.

17. The encoder spectrograph of claim 1, further comprising:

an entrance aperture, the received incident beam passing through the entrance aperture towards the concave diffraction grating.

18. The encoder spectrograph of claim 1, further comprising:

a detector aperture, the overlapping image passing through the detector aperture from the detector lens towards the detector element.

19. The encoder spectrograph of claim 1, the spatial light modulator having a circular shape and a diameter in a plane containing the surface of the modulator, wherein an optical path from the spatial light modulator to the detector element is less than the diameter of the spatial light modulator.

20. The encoder spectrograph of claim 19, wherein the overlapping image on the detector element is less than 4 mm in any dimension.

21. The encoder spectrograph of claim 1, wherein the crossover fast collection optic and the detector lens are the only optical elements in an optical path between the spatial light modulator and the detector element.

22. The encoder spectrograph of claim 1, further comprising:

a printed circuit board coupled to the detector element for receiving signals representing the overlapping image, the printed circuit board having a cutaway portion through which the received incident beam passes.

23. The encoder spectrograph of claim 1, wherein the crossover focusing reflector, the crossover fast collection optic, and the detector lens are mounted in a single optics bracket.

24. The encoder spectrograph of claim 23, wherein the concave diffraction grating is mounted in a grating mount that is detachably attachable to the optics bracket.

25. The encoder spectrograph of claim 1, wherein the crossover focusing reflector, the crossover fast collection optic, and the detector lens are combined into a single injection-molded optics bracket.

26. The method of claim 25, wherein the crossover focusing reflector and the crossover fast collection optic are formed by evaporating metallic surfaces on the injection-molded optic.

27. An encoder spectrograph for encoding and detecting one or more spectral components of a received radiation beam, the encoder spectrograph comprising:

first optics dispersing a received incident beam of radiation by wavelength and redirecting the dispersed beam across the incident beam to form an image dispersed by wavelength along a dispersion axis;

a spatial light modulator positioned to receive the dispersed image on a surface thereof, the spatial light modulator modulating the intensity of the dispersed image by a position along the dispersion axis to provide an encoded beam;

second optics collecting the encoded beam from the spatial light modulator, redirecting the encoded beam across the dispersed beam, and focusing the encoded beam to form a substantially overlapping image; and

a detector element positioned to receive the overlapping image and produce a signal representative of the encoded beam.

28. The encoder spectrograph of claim 27, wherein the second optics consists solely of a single reflective element and a single lens element.

29. A dual encoder spectrograph for encoding and detecting one or more spectral components of each of two received radiation beams, the encoder spectrograph comprising:

first dispersing optics dispersing a first received incident beam of radiation by wavelength and redirecting the first dispersed beam across the first incident beam to form a first image dispersed by wavelength along a first dispersion axis;

second dispersing optics dispersing a second received incident beam of radiation by wavelength and redirecting the second dispersed beam across the second incident beam to form a second image dispersed by wavelength along a second dispersion axis;

a spatial light modulator positioned to receive the first and second dispersed images on a surface thereof, the spatial light modulator modulating the intensity of each of the first and second dispersed images by a position along the corresponding first and second dispersion axes to provide a first encoded beam and a second encoded beam;

first collecting optics collecting the first encoded beam from the spatial light modulator, redirecting the first encoded beam across the first dispersed beam, and focusing the first encoded beam to form a substantially first overlapping image; and

second collecting optics collecting the second encoded beam from the spatial light modulator, redirecting the second encoded beam across the second dispersed beam, and focusing the second encoded beam to form a substantially overlapping second image;

a first detector element positioned to receive the first overlapping image and produce a first signal representative of the first encoded beam; and

a second detector element positioned to receive the second overlapping image and produce a second signal representative of the second encoded beam.

30. The encoder spectrograph of claim 29, wherein the first and second incident beams are received on the same side of the dual encoder spectrograph.