Mid-infrared hyperspectral spectroscopy systems and methods therefor

• US 9,518,917 B2
• Filed: 03/09/2016
• Issued: 12/13/2016
• Est. Priority Date: 03/09/2015
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Scherer, Axel, Hartley, Frank T.
• Primary Examiner(s): Bryant, Casey
• Application Number:
  US15/065,792
• Publication Number:
  US 20160266035A1
• Time in Patent Office: 279 Days
• US Class Current: 1/1
• CPC Class Codes: G01J 2003/1213 Filters in general, e.g. dichroic, band
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/0256 Compact construction
• CPC Class Codes: G01J 3/108 for measurement in the infrared range
• CPC Class Codes: G01J 3/18 using diffraction elements, e.g. grating gratings per se G02B
• CPC Class Codes: G01J 3/36 Investigating two or more bands of a spectrum by separate detectors
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/3148 using three or more wavelengths
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/3577 for analysing liquids, e.g. polluted water
• CPC Class Codes: G01N 2201/0245 with insertable-removable part
• CPC Class Codes: G01N 2201/0638 Refractive parts

Abstract

MIR spectroscopy systems comprising hierarchical spectral dispersion that enables fine spectral resolution and high sensitivity spectroscopy are disclosed. Hierarchical spectral dispersion is derived by employing at least two diffractive lens arrays, located on either side of a test sample, each receiving input radiation having an input spectral range and distributing the input radiation into a plurality of output signals, each having a fraction of the spectral range of the input radiation. As a result, the signal multiplication factor of the two arrays is multiplied in a manner that mitigates the propagation of wavelength harmonics through the system. In some embodiments, an emitter array comprising a plurality of spectrally selective emitters provides the input MIR radiation to a spectroscopy system. In some embodiments, spectrally selective detectors are used to detect narrow spectral components in the radiation after they have passed through the test sample.

Claims

1. A mid-infrared (MIR) spectroscopy system for detecting an analyte in a test sample, the spectroscopy system comprising:

(1) a hierarchical spectral dispersion system comprising;

(a) a first plurality of lenses arranged to receive a plurality of radiation signals, each having a different first spectral range, the plurality of first spectral ranges collectively spanning at least a portion of the MIR spectrum, each lens of the first plurality thereof being operative for receiving a different radiation signal of the plurality thereof and distributing it into a plurality of radiation beams focused at a first focal field after interacting with the test sample, wherein each radiation beam has a second spectral range that is smaller than the first spectral range, and wherein the plurality of second spectral ranges is collectively equal to the first spectral range; and

(b) a second plurality of lenses located at the first focal field, each lens of the second plurality thereof being operative for receiving a different radiation beam of the plurality thereof and distributing it into a plurality of radiation beamlets focused at a second focal field, wherein each radiation beamlet has a different third spectral range that is smaller than the second spectral range of its respective radiation beam, and wherein the plurality of third spectral ranges is collectively equal to the second spectral range; and

(2) a first plurality of detector pixels located at the second focal field, the first plurality of detector pixels being arranged such that each detector pixel receives a different radiation beamlet of the plurality thereof;

wherein the plurality of first spectral ranges collectively spans the MIR spectrum.

2. The spectroscopy system of claim 1 wherein a first detector pixel of the first plurality thereof is substantially spectrally selective for the third spectral range of the radiation beamlet it receives.

3. The spectroscopy system of claim 2 wherein the first detector pixel comprises a first material that is substantially transparent for MIR radiation, the first detector pixel including a first arrangement of features that collectively defines a photonic crystal, wherein the size and spacing of the features are based on the third spectral range of the radiation beamlet it receives.

4. The spectroscopy system of claim 3 wherein the first material is float-zone silicon.

5. The spectroscopy system of claim 3 wherein the features are dimensioned and arranged to give rise to surface states that enable the absorption of MIR radiation and the generation of charge-carriers in the first material.

6. The spectroscopy system of claim 5 wherein the first pixel includes first and second contacts that are operative for inducing avalanche gain in the first material.

7. The spectroscopy system of claim 1 further comprising a first detector comprising a second plurality of detector pixels that is collectively spectrally selective for a first radiation signal of the plurality thereof, the first plurality of detector pixels including the second plurality of detector pixels, wherein the second plurality of pixels includes a first detector pixel and a second detector pixel, and wherein the first detector pixel is substantially spectrally selective for the third spectral range of the radiation beamlet it receives and the second detector pixel is a blind pixel.

8. The spectroscopy system of claim 1 further comprising (3) a plurality of emitters, each emitter of the plurality thereof emitting a different radiation signal of the plurality thereof.

9. The spectroscopy system of claim 8 wherein a first emitter of the plurality thereof comprises a filament that is dimensioned and arranged to emit a first radiation signal of the plurality thereof, the filament including a plurality of emitting elements characterized by a first emitter width and first emitter spacing, the first emitter width and first emitter spacing being based on the first spectral range of the first radiation signal.

10. The spectroscopy system of claim 9 wherein the first emitter further comprises a mirror, the mirror and the filament collectively defining a resonant cavity having a cavity length that is based on the first spectral range of the first radiation signal.

11. The spectroscopy system of claim 1 wherein a first lens of the second plurality thereof distributes its respective radiation beamlets such that they are focused at a first plurality of spots at the second focal field, and wherein the first lens is dimensioned and arranged to focus scatter radiation received from the test sample at a second plurality of spots on the second focal field, wherein the first plurality of spots and second plurality of spots are each arranged such that each spot is uniquely characterized by a different third spectral range of the plurality thereof.

12. The spectroscopy system of claim 1 further comprising (3) a sample cuvette for holding the test sample, wherein the sample cuvette includes the first plurality of lenses, the second plurality of lenses and the plurality of detector pixels.

13. The spectroscopy system of claim 1 further comprising:

(3) a docking station, the docking station including a receiver for receiving a sample cuvette, the first plurality of lenses, the second plurality of lenses and the plurality of detector pixels; and

(4) the sample cuvette for holding the test sample, wherein the sample cuvette includes;

(a) a body comprising a first material that is substantially transparent for MIR radiation; and

(b) a sample chamber for locating the test sample;

wherein the sample cuvette is dimensioned and arranged to be removably located within the receiver.

14. A hyperspectral spectroscopy system comprising:

a hierarchical spectral dispersion system that is dimensioned and arranged to distribute the spectral components of a first plurality of radiation signals into a plurality of radiation beamlets, the first plurality of radiation signals collectively spanning a first spectral range that is at least a portion of the mid-infrared (MIR) spectrum, and each radiation beamlet including a different spectral component included in the first spectral range such that the plurality of spectral components collectively spans the first spectral range, each spectral component having a second spectral range that is smaller than the first spectral range; and

a plurality of detectors, each detector including a plurality of detector pixels, and each detector pixel being spectrally selective such that it detects only one spectral component of the plurality thereof;

wherein the hierarchical spectral dispersion system and the plurality of detectors are arranged such that each radiation beamlet of the plurality thereof is directed to the detector pixel that is spectrally selective for its respective spectral component.

15. The spectroscopy system of claim 14 wherein the hierarchical spectral dispersion system includes:

a plurality of first lenses, each first lens being arranged to distribute a different radiation signal of the first plurality thereof into a plurality of radiation beams, each radiation beam having a third spectral range that is smaller than the first spectral range and larger than the second spectral range; and

a plurality of second lenses, each second lens including a plurality of lenslets, and each lenslet being arranged to receive a different radiation beam of the plurality thereof and distribute it into a different radiation beamlet of the plurality thereof.

16. The spectroscopy system of claim 14 wherein a first detector is spectrally selective for a first radiation signal of the plurality thereof, and wherein a first detector pixel of the first detector is substantially spectrally selective for a first spectral component of the first radiation signal, and further wherein a second detector pixel of the first detector is a blind pixel.

17. The spectroscopy system of claim 14 wherein a first detector pixel of a first detector of the plurality thereof comprises a first material that is substantially transparent for MIR radiation, the first detector pixel including a first arrangement of features that collectively defines a photonic crystal, wherein the size and spacing of the features are based on the spectral component of the radiation beamlet it receives.

18. The spectroscopy system of claim 14 further comprising a plurality of emitters, each emitter being operative for providing a different radiation signal of the first plurality thereof.

19. The spectroscopy system of claim 18 wherein a first emitter of the plurality thereof comprises a filament that is dimensioned and arranged to emit a first radiation signal of the plurality thereof, the filament including a plurality of emitting elements characterized by a first emitter width and first emitter spacing, the first emitter width and first emitter spacing being based on the first spectral range of the first radiation signal.

20. The spectroscopy system of claim 19 wherein the first emitter further comprises a mirror, the mirror and the filament collectively defining a resonant cavity having a cavity length that is based on the first spectral range of the first radiation signal.

21. A method for analyzing a test sample, the method comprising:

distributing each of a first plurality of radiation signals into a first plurality of radiation beams, each radiation signal being characterized by a different first spectral range such that the plurality of first spectral ranges collectively spans at least a portion of the MIR spectrum;

focusing each radiation beam of the first plurality thereof at a first focal field such that the first plurality of radiation beams interacts with the test sample to give rise to a second plurality of radiation beams whose spectral content is based on the chemical composition of the test sample, wherein each radiation beam of the second plurality thereof has a different second spectral range that is smaller than the first spectral range of its respective radiation signal, and wherein each plurality of second spectral ranges collectively spans the first spectral range of its respective radiation signal;

distributing each radiation beam of the second plurality thereof into a plurality of radiation beamlets that are focused at a second focal field, each radiation beamlet having a spectral component characterized by a different third spectral range that is smaller than the second spectral range of its respective radiation beam of the second plurality thereof, and wherein each plurality of third spectral ranges collectively spans the second spectral range of its respective radiation beam of the second plurality thereof;

detecting the plurality of radiation beamlets at a plurality of detectors located at the second focal field, wherein each detector provides an output signal based on respective radiation beamlet; and

detecting at least one analyte in the test sample based on the plurality of output signals.

22. The method of claim 21 further including providing the plurality of detectors such that each detector is non-spectrally selective radiation.

23. The method of claim 21 further including:

providing a first detector of the plurality thereof such that the first detector is spectrally selective for the spectral component of a first beamlet of the plurality thereof; and

focusing the first beamlet at the first detector.

24. The method of claim 21 further including providing a first detector of the plurality thereof such that the first detector comprises:

a first material that is substantially transparent for MIR radiation; and

a first arrangement of features that collectively defines a photonic crystal, wherein the size and spacing of the features are based on the spectral component of the radiation beamlet it receives.

25. The method of claim 24 further including:

providing a second detector of the plurality thereof such that the second detector is a blind detector; and

comparing a first output signal provided by the first detector and a second output signal provided by the second detector.

26. The method of claim 24 further including reading out the first detector by operations comprising:

providing an electric field across the first detector during a first portion of a pulse period;

providing no electric field across the first detector during a second portion of the pulse period;

measuring the photoconductance of the first pixel during the first portion; and

measuring the temperature of the first pixel during the second portion.

27. The spectroscopy system of claim 21 further comprising:

providing a plurality of emitters, each emitter being operative for selectively emitting a different radiation signal of the first plurality thereof; and

enabling each of the plurality of emitters to emit its respective radiation signal.

28. The spectroscopy system of claim 27 wherein the plurality of emitters are energized one at a time.

29. The spectroscopy system of claim 27 wherein a first emitter of the plurality thereof is provided such that it comprises a filament that is dimensioned and arranged to emit a first radiation signal of the first plurality thereof, the filament including a plurality of emitting elements characterized by a first emitter width and first emitter spacing, the first emitter width and first emitter spacing being based on the first spectral range of the first radiation signal.

30. The spectroscopy system of claim 29 wherein the first emitter is provided such that it further comprises a mirror, the mirror and the filament collectively defining a resonant cavity having a cavity length that is based on the first spectral range of the first radiation signal.