Grating spectrometer

• US 4,997,281 A
• Filed: 08/24/1989
• Issued: 03/05/1991
• Est. Priority Date: 08/24/1989
• Status: Expired due to Term

• Current Assignee: Stark, Edward W.
• Original Assignee: Stark, Edward W.
• Inventors: Stark, Edward W.
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US07/398,094
• Time in Patent Office: 558 Days
• Field of Search: 356/305, 356/328, 356/326, 356/319, 356/51, 356/331, 356/334, 250/339
• US Class Current: 356/328
• CPC Class Codes: G01J 2003/1828 with order sorter or prefilter
• CPC Class Codes: G01J 3/1838 Holographic gratings
• CPC Class Codes: G01J 3/2803 using photoelectric array detector

Abstract

An improved flat field grating spectrometer for increasing the spectral resolutiion and usable spectral range. The spectrometer comprises an entrance slit or port, a concave grating, a field flattening lens and detection means encompassing the desired spectral region and capable of providing separate measurements between different regions of the spectral image plane. A second embodiment provides a beam splitter (dichroic or neutral density) placed between the grating and the detector to divert a portion of the energy at selected wavelengths through a second field flattening lens to a second detection means.

Claims

1. A flat field grating spectrometer having increased spectral resolution and usable spectral range comprises:

an entrance slit or port for selection of incident spectral energy to be measured;

a concave holographic grating for receiving said spectral energy from said slit or port and for dispersing and imaging the incident spectral energy;

a field flattening lens for flattening the field of the energy dispersed and imaged by said grating; and

detector means for measuring the flattened spectral image provided by said field flattening lens, said detector means being in the form of a planar array of detecting elements for providing signals responsive to said flattened spectral image.

2. A spectrometer in accordance with claim 1, also including an order sorting filter for transmitting energy in a desired diffraction order and absorbing or reflecting energy in other orders to which the detector means is responsive.

3. A spectrometer in accordance with claim 1 wherein said detector means includes a beam splitter placed in the path of energy directed to said field flattening lens from said grating, said beam splitter allowing a portion of the energy incident on said beam splitter to pass to said field flattening lens and a portion of said energy incident on said beam splitter to be reflected;

a further field flattening lens for redirecting said reflecting energy and a further detector array responsive to said reflected energy also being included.

4. A spectrometer in accordance with claim 3 wherein said beam splitter is of the dichroic kind.

5. A spectrometer in accordance with claim 3 wherein said beam splitter is a neutral beam splitter.

6. A spectrometer in accordance with claim 5 wherein the ratio of energy transmission is adjusted to substantially equalize the signals provided from the detector arrays.

7. A spectrometer in accordance with claim 3 wherein said beam splitter includes an optical element which reflects or transmits optical energy in response to a signal to switch between said detector arrays.

8. A spectrometer in accordance with claim 7 wherein said optical element in said beam splitter is an electro-optically active material.

9. A spectrometer in accordance with claim 1 wherein said field flattening lens and grating each have a principal axis respectively, the angle being formed between said principal axes being less than 45°

.

10. A spectrometer as in claim 1 wherein the grating has a principal axis and the entrance slit is located near the principal axis of the grating so that the zero order image of the slit is close to the principal axis of the grating.

11. A spectrometer in accordance with claim 1 also including electronic processing means responsive to the signal from said array of detecting elements of said detector means.

12. A spectrometer in accordance with claim 11 wherein said electronic processing means includes a preamplifier and multiplexer.

13. A spectrometer in accordance with claim 3 wherein said first mentioned detector array is formed of silicon photodiodes and said further detector array is formed of germanium or indium gallium arsenide photodiodes.

14. A spectrometer in accordance with claim 3 wherein said first mentioned detector array is responsive within the range of wavelengths from 515 to 1100 nm while the further detector array is responsive within the range of wavelengths from 1030 to 1800 nm.

15. A spectrometer in accordance with claim 3 wherein said first mentioned detector array is responsive to one order of said grating and said further detector array is responsive to a second order of said grating.

16. A spectrometer comprising:

an entrance slit or port for selection of incident spectral energy to be measured;

a concave holographic grating for receiving said spectral energy from said slit or port and for dispersing and imaging the incident spectral energy;

first detector means for measuring a spectral image and for providing first signals responsive thereto;

a beam splitter placed in the path of energy directed toward said first detector means from said grating for creating first and second spectral images, said beam splitter allowing a portion of the energy incident on said beam splitter to pass to said first detector means as said first spectral image and a portion of said energy incident on said beam splitter to be reflected as said second spectral image; and

second detector means responsive to the reflected energy of said second spectral image from said beam splitter for providing second signals responsive to said second spectral image.

17. A spectrometer in accordance with claim 16 wherein the energy transmitted by said beam splitter is adjusted with respect to the reflected energy so that the magnitude of the signals from the first and second detectors are equal.

18. A spectrometer in accordance with claim 16 also including an order sorting filter for transmitting energy in a desired diffraction order and absorbing or reflecting energy in other orders to which the detector means is responsive.

19. A spectrometer in accordance with claim 16 wherein said beam splitter is of the dichroic kind.

20. A spectrometer in accordance with claim 16 wherein said beam splitter is a neutral beam splitter.

21. A spectrometer in accordance with claim 20 wherein the ratio of energy transmission is adjusted to substantially equalize the signals provided from the first and second detector means.

22. A spectrometer in accordance with claim 16 wherein said beam splitter includes an optical element which reflects or transmits optical energy in response to a signal to switch between said first and second detector means.

23. A spectrometer in accordance with claim 22 wherein said optical element in said beam splitter is an electro-optically active material.

24. A spectrometer as in claim 16 wherein the angle between a normal to the first detector means and the grating is less than 45°

.

25. A spectrometer as in claim 16 wherein the grating has a principal axis and the entrance slit is located near the principal axis of the grating so that the zero order image of the slit is close to the principal axis of the grating.

26. A spectrometer in accordance with claim 16 wherein said first and second detector means include a first and second array of detecting elements respectively and wherein electronic processing means responsive to the signal from each said array of detecting elements are included.

27. A spectrometer in accordance with claim 26 wherein said electronic processing means includes a preamplifier and multiplexer.

28. A spectrometer in accordance with claim 16 wherein said first detecting means includes a first array of detecting element and said second detecting means include a second array of detecting elements and wherein said first detector array is formed of silicon photodiodes and said second detector array is formed of germanium or indium gallium arsenide photodiodes.

29. A spectrometer in accordance with claim 16 wherein said first detecting means includes a first array of detecting element and said second detecting means include a second array of detecting elements and wherein said first detector array is responsive within the range of wavelengths from 515 to 1100 nm while the second detector array is responsive within the range of wavelengths from 1030 to 1800 nm.