System and method for changing spectral range of a cryogenically cooled detector

• US 9,157,806 B2
• Filed: 02/17/2011
• Issued: 10/13/2015
• Est. Priority Date: 02/18/2010
• Status: Active Grant

• Current Assignee: Rafael Advanced Defense Systems Limited (Government of Israel)
• Original Assignee: Rafael Advanced Defense Systems Limited (Government of Israel)
• Inventors: Yaacobi, Ami
• Primary Examiner(s): Taningco, Marcus
• Assistant Examiner(s): Malevic, Djura
• Application Number:
  US13/029,174
• Publication Number:
  US 20110199605A1
• Time in Patent Office: 1,699 Days
• Field of Search: 250/338.1
• US Class Current: 1/1
• CPC Class Codes: G01J 5/06 Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity for adjusting of solid angle of collected radiation G01J5/07; means for wavelength selection G01J5/0801
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0808 Convex mirrors
• CPC Class Codes: G01J 5/084 Adjustable or slidable
• CPC Class Codes: G01J 5/602 using selective, monochromatic or bandpass filtering

Abstract

The provided optical system allows selective spectral transfer of radiation, and provides a reflecting field of view at an undesired range directed towards cold surfaces. A removable spectral filter having a high transmittance at a first spectral range and a low transmittance at a second spectral range is disposed outside a cold shield. A reflective surface faces the detecting device and provides the detector a reflecting field of view at the second spectral range directed back towards the cold shield, and a blackened cold skirt thereof. Alternatively, a dichroic mirror is disposed inside the cold shield and has a high reflectance at a first spectral range and a high transmittance at a second range. The detecting device includes a first and a second arm of the cold shield to accommodate respective optical channels.

Claims

1. An optical system comprising:

(a) an infra-red detector disposed within a cryogenically cooled cold shield;

(b) a spectral filter for allowing transfer to said infra-red detector of incoming radiation at a desired spectral range while preventing transfer thereof at an undesired spectral range;

(c) said spectral filter being disposable into and removable from a position outside the cold shield, the disposing and removing of said spectral filter facilitating respective changes of the operational spectral range;

(d) a surface of said spectral filter having high reflectance at said undesired spectral range while having high transmittance at said desired spectral range; and

(e) the position of said spectral filter and said high reflectance of its surface being adapted for providing at the detector a reflected field of view at said undesired spectral range directed towards at least one cold blackened surface.

2. The optical system of claim 1, wherein the spectral filter has a high transmittance at a first spectral range and a substantially lower transmittance for a second spectral range.

3. The optical system of claim 2 wherein said high transmittance is higher than 70% and said low transmittance is lower than 20%.

4. The optical system of claim 1, wherein the optical system further includes a blackened cold skirt surrounding a coupling window of the cold shield and said reflective surface providing the detector a reflecting field of view directed towards the cold shield and said blackened cold skirt.

5. The optical system of claim 1 wherein said reflective surface is a concave reflecting surface facing the detecting device.

6. The optical system of claim 1 wherein a dichroic mirror is disposed inside the cold shield in front of a single infra-red detector, said dichroic mirror has a high reflectance at a first spectral range and a high transmittance at a second spectral range, and the optical system includes a first arm and a second arm of the cold shield to accommodate respective optical channels for directing said first spectral range and for said second spectral range towards said single infra-red detector.

7. The optical system of claim 6 wherein the system includes an optical train for providing a reflecting field of view at said undesired spectral range directed towards at least one cold surface.

8. The optical system of claim 7 wherein said at least one cold surface is a blackened surface of the cold shield.

9. The optical system of claim 7 wherein said at least one cold surface is a thermo-electric cooler disposed outside the cold shield.

10. A method for changing an operational spectral range of a cryogenically cooled infra-red detecting device, the device having an infra-red detector disposed within a cold shield, and being adapted for receiving incoming radiation, the method comprising:

(a) placing a spectral filter outside the cold shield for changing an operational spectral range of the detecting device, a surface of said spectral filter having high reflectance at an undesired spectral range while having high transmittance at a desired spectral range. said spectral filter adapted for;

(i) transferring to the detector incoming radiation at said desired spectral range;

(ii) preventing transfer thereof at said undesired spectral range; and

(iii) providing at the detector a reflected field of view at said undesired spectral range directed towards at least one cold blackened surface by said surface of said spectral filter;

and

(b) removing said spectral filter.

11. The method of claim 10 wherein the method includes disposing, a dichroic mirror inside the cold shield in front of single infra-red detector, said dichroic mirror has a high reflectance at a first spectral range and a high transmittance at a second spectral range, and the detecting device includes a first arm and a second arm of the cold shield to accommodate respective optical channels for directing said first spectral range and for said second spectral range towards said single infra-red detector.

12. The method of claim 11 wherein the method includes providing an optical train for providing a reflecting field of view at said undesired spectral range directed towards at least one cold surface.