Optical system for simultaneous imaging of LWIR and millimeter wave radiation

• US 6,919,988 B2
• Filed: 05/06/2002
• Issued: 07/19/2005
• Est. Priority Date: 05/06/2002
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Cook, Lacy G.
• Primary Examiner(s): Dunn, Drew A.
• Assistant Examiner(s): Pritchett, Joshua L.
• Application Number:
  US10/139,943
• Publication Number:
  US 20030206338A1
• Time in Patent Office: 1,170 Days
• Field of Search: 359/350, 359/356, 359/366, 359/857
• US Class Current: 359/356
• CPC Class Codes: G02B 17/0804 using two curved mirrors G02B17/0864, G02B17/0896 takes precedence
• CPC Class Codes: G02B 17/0852 having a field corrector only
• CPC Class Codes: G02B 17/0856 comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors
• CPC Class Codes: G02B 17/0896 with variable magnification or multiple imaging planes, including multispectral systems systems with only refractive elements G02B15/14

Abstract

A system and method for simultaneous imaging of both infrared and millimeter wave radiation. The novel optical system (10) includes a primary mirror (20), a Mangin secondary mirror (30) positioned to receive energy reflected from the primary mirror (20), and an immersion lens (40) for focusing energy received from the Mangin mirror (30). In the illustrative embodiment, the primary mirror (20) and Mangin mirror (30) are arranged in a Cassegrain configuration. Central to this invention is the use of a negative power refractive Mangin mirror (30) as the Cassegrain secondary mirror, so that the field curvature of the secondary mirror (30) and immersion lens (40) can be made to cancel. The immersion lens (40) effectively decreases the wavelength of the millimeter wave radiation, allowing a smaller detector to collect the same amount of radiation as would a larger detector in air. In the illustrative embodiment, the system (10) further includes a detector array (52) placed in intimate contact with the immersion lens (40).

Claims

1. An optical system for imaging electromagnetic energy in first and second wavelength bands, said first wavelength band being in the infrared region of the electromagnetic spectrum and said second wavelength being in the millimeter wave region of the electromagnetic spectrum, said system comprising:

a primary mirror reflective at said first and second wavelength bands;

a Mangin mirror positioned to receive energy reflected from said primary mirror; and

an immersion lens for focusing energy received from said Mangin mirror,

wherein said Mangin mirror and said immersion lens are designed such that their combined field curvature is approximately zero.

2. The invention of claim 1 wherein said first wavelength band is long wavelength infrared.

3. The invention of claim 1 wherein said primary mirror and said Mangin mirror are arranged in a Cassegrain configuration.

4. The invention of claim 1 wherein said Mangin mirror is comprised of a layer of material transmissive at said first and second wavelength bands with first and second surfaces.

5. The invention of claim 4, wherein said second surface is coated with a material which is reflective at said first and second wavelength bands.

6. The invention of claim 4 wherein said first surface is coated with an anti-reflective coating.

7. The invention of claim 1 wherein said immersion lens has a hemispherical first surface and a flat second surface.

8. The invention of claim 7 wherein said immersion lens is comprised of material transmissive at said first and second wavelength bands.

9. The invention of claim 8 wherein said material has a high index of refraction.

10. The invention of claim 7 wherein said optical system further includes a detector array.

11. The invention of claim 10 wherein said detector array is in intimate contact with the second surface of said immersion lens.

12. The invention of claim 10 wherein the center of curvature of the first surface of said immersion lens is at the surface of said detector array.

13. The invention of claim 10 wherein said detector array is capable of sensing at said first and second wavelength bands.

14. The invention of claim 1 wherein said optical system further includes means for correcting chromatic aberrations.

15. The invention of claim 14 wherein said means for correcting chromatic aberrations is a diffraction grating.

16. A system for simultaneous imaging of infrared and millimeter wave energy comprising:

a primary mirror reflective at infrared and millimeter wavelengths;

a Mangin mirror positioned to receive energy reflected from said primary mirror;

an immersion lens for focusing energy received from said Mangin mirror;

a detector array in intimate contact with said immersion lens; and

a signal processor for processing signals from said detector array,

wherein said Mangin mirror and said immersion lens are designed such that their combined field curvature is approximately zero.

17. A method for simultaneous imaging of infrared and millimeter wave energy including the steps of:

reflecting said energy onto a Mangin mirror using a primary mirror reflective at infrared and millimeter wavelengths;

correcting for aberrations with said Mangin mirror; and

focusing energy from said Mangin mirror onto a focal plane using an immersion lens;

wherein said step of correcting for aberrations includes compensating for field curvature such that the combined field curvature of said Mangin mirror and said immersion lens is approximately zero.