Mid-wave and long-wave infrared point spectrometer

Patent metadata

Field	Value
Publication number	US-11719576-B2
Application number	US-202017083165-A
Country	US
Kind code	B2
Filing date	Oct 28, 2020
Priority date	Nov 1, 2019
Publication date	Aug 8, 2023
Grant date	Aug 8, 2023

Abstract

Methods and devices to implement mid-wave and long-wave infrared point spectrometers are disclosed. The described methods and devices involve bi-faceted gratings, high-operating-temperature barrier infrared and thermal detectors. The disclosed concept can be used to design flight spectrometers that cover broad solar reflectance plus thermal emission spectral ranges with a compact and low-cost instrument suitable for small spacecraft reconnaissance of asteroids, the Moon, and planetary satellites as well as mass-constrained landed missions.

First claim

The invention claimed is:

1. A spectrometer comprising:
an optical assembly including a telescope, a grating and a relay system; and
a focal plane module including a first detector and a second detector,

wherein:
i) the optical assembly is configured to:
receive light from an object or scene through the telescope, thereby focusing the light, receive the focused light by the grating through the relay system; and
split the received light by the grating into a first beam within a first spectral range and a second beam within a second spectral range different from the first spectral range, and

ii) the focal plane module is configured to:
receive the first beam by the first detector to generate a first output signal in correspondence with a spectral content of the first beam, and
receive the second beam by the second detector to generate a second output signal in correspondence with a spectral content of the second beam;

iii) the relay system comprises a first relay with three mirrors, and
iv) the grating is disposed on a secondary mirror of the first relay.

2. The spectrometer of claim 1 , wherein the relay system further comprises a second relay configured to focus the first beam and the second beam onto the focal plane module.

3. The spectrometer of claim 1 , wherein the grating is a bi-faceted grating comprising two diffraction grating patterns on a mirror substrate with a different diffraction grating written on each facet of the mirror substrate.

4. The spectrometer of claim 1 , wherein the first spectral range includes a mid-wave infrared spectral range and the second spectral range include a long-wave infrared spectral range, and wherein the mid-wave infrared spectral range includes wavelengths in a range of 2 μm to 4 μm, and the long-wave infrared spectral range includes wavelengths in a range of 5.5 μm to 12 μm.

5. The spectrometer of claim 1 , further comprising a pinhole disposed between the telescope module and the relay system.

6. A spacecraft comprising the spectrometer of claim 1 .

7. A spectrometer comprising:
an optical assembly including a telescope, a grating and a relay system; and
a focal plane module including a first detector and a second detector,

wherein:
i) the optical assembly is configured to:
receive light from an object or scene through the telescope, thereby focusing the light, receive the focused light by the grating through the relay system; and
split the received light by the grating into a first beam within a first spectral range and a second beam within a second spectral range different from the first spectral range, and

ii) the focal plane module is configured to:
receive the first beam by the first detector to generate a first output signal in correspondence with a spectral content of the first beam, and
receive the second beam by the second detector to generate a second output signal in correspondence with a spectral content of the second beam;

iii) the first detector comprises a high-operating-temperature barrier infrared detector and the second detector comprises a thermal detector, and
iv) the first spectral range includes a mid-wave infrared spectral range and the second spectral range include a long-wave infrared spectral range.

8. The spectrometer of claim 7 , wherein the high-operating-temperature barrier infrared detector comprises a two-dimensional focal plan array, and wherein the thermal detector comprises a line array of micro-sized thermopile detectors.

9. The spectrometer of claim 7 , wherein in operative conditions a temperature of the high-operating-temperature barrier infrared detector is maintained at a colder than ambient temperature and a temperature of the thermal detector is at ambient temperature.

10. The spectrometer of claim 9 , further comprising a cryocooler including cryocooler electronics, the cryocooler being configured to maintain temperature of the high-operating-temperature barrier infrared detector at the colder than ambient temperature.

11. The spectrometer of claim 10 , wherein:
the first detector further comprises a first readout integrated circuit (ROIC) coupled to the high-operating-temperature barrier infrared detector, a first printed wire assembly (PWA) and a cold plate;
the second detector further comprises a second ROIC coupled to the thermal detector, a second PWA and an ambient plate;
a combination of the high-operating-temperature barrier infrared detector and the first ROIC are disposed on the first PWA bonded to the cold plate; and
a combination of the thermal detector and the second ROIC are disposed on the second PWA bonded to the ambient plate.

12. The spectrometer of claim 11 , wherein the first ROIC is configured to generate the first output signal and the second ROIC is configured to generate the second output signal.

13. The spectrometer of claim 12 , further comprising payload electronics configured to control the cryocooler electronics and to receive the first and the second output signal for analysis and storage.

14. The spectrometer of claim 13 , wherein each of the first detector and the second detector comprises filters to filter out unwanted light.

15. The spectrometer of claim 14 , wherein the first detector comprises a cold shield configured to receive the first beam, and wherein the second detector comprises an ambient shield configured to receive the second beam.

16. A method of spectrometry comprising:
receiving light from an object or a scene;
focusing the light;
receiving the focused light by a grating through a relay system, the relay system including a first relay with three mirrors and the grating being disposed on a secondary mirror of the first relay;
splitting the focused light by the grating into a first beam within a first spectral range and a second beam within a second spectral range;
focusing the first beam on a first detector and the second beam on a second detector;
generating by the first detector a first output signal in correspondence with a spectral content of the first beam; and

generating by the second detector a second output signal in correspondence with a spectral content of the second beam.

17. The method of claim 16 , wherein the first spectral range includes a mid-wave infrared spectral range and the second spectral range include a long-wave infrared spectral range.

18. The method of claim 16 , further comprising maintaining the first detector at a cold temperature and the second detector at an ambient temperature.

Assignees

• California Inst Of Techn

Inventors

• Johnson William R
• Kenyon Matthew E
• Blacksberg Jordana
• Raymond Carol A
• Ehlmann Bethany L
• Chen Xiangwen

Classifications

• G01J3/2803 Primary

  using photoelectric array detector · CPC title

• B64G1/66

  Arrangements or adaptations of apparatus or instruments, not otherwise provided for · CPC title

• G01J3/021

  using plane or convex mirrors, parallel phase plates, or particular reflectors · CPC title

• G01J3/0286

  Constructional arrangements for compensating for fluctuations caused by temperature, humidity or pressure, or using cooling or temperature stabilization of parts of the device; Controlling the atmosphere inside a spectrometer, e.g. vacuum · CPC title

• G01J3/18

  using diffraction elements, e.g. grating (gratings per se G02B) · CPC title