Achromatic lens for millimeter-wave and infrared bands

• US 6,665,116 B1
• Filed: 07/10/2000
• Issued: 12/16/2003
• Est. Priority Date: 07/10/2000
• Status: Expired due to Fees

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Dolezal, Franklin A, Harvey, Robin J.
• Primary Examiner(s): Juba, John
• Assistant Examiner(s): ASSAF, FAYEZ G
• Application Number:
  US09/612,846
• Time in Patent Office: 1,254 Days
• Field of Search: 359/350, 359/355, 359/356, 359/361, 250/339.01
• US Class Current: 359/355
• CPC Class Codes: G02B 13/146 with corrections for use in multiple wavelength bands, such as infrared and visible light, e.g. FLIR systems
• CPC Class Codes: Y10S 359/90 Methods

Abstract

The present invention relates to a method for designing an achromatic lens and a lens according to the design. The invention provides a lens that makes use of the differences in the index of refraction of ZnSe and ZnS in the mm-wave and IR wavebands to minimize the differences in focal position between the two wavebands. This lens train can be used in conjunction with a dual-band focal plane array to simultaneously focus two wavebands on a common focal plane and thus provide for simultaneous imaging in both wavebands.

Claims

1. An multi element apparatus capable of simultaneously focusing a plurality of wavebands in substantially the same focal plane, comprising:

i. a first element comprising a first composition and having a thickness, a perimeter, a first index of refraction, and a first and second surface substantially perpendicular to said perimeter wherein said first surface has a first geometry and wherein said second surface has a second geometry;

ii. a second element comprising a second composition and having a thickness, a perimeter, a second index of refraction, and a first and second surface substantially perpendicular to said perimeter wherein said first surface has a third geometry and wherein said second surface has a fourth geometry; and

iii. said first and second elements are aligned such that the second surface of the first element and the first surface of the second element are in substantial conformity with each other and aligned such that the perimeters essentially form a column, wherein

the plurality of wavebands include millimeter wave radiation and infrared radiation, wherein;

i. millimeter wave radiation is between 30 GHz and 300 GHz; and

ii. infrared radiation is between 0.75 and 750 micrometers.

2. A multi element apparatus as set forth in claim 1, wherein:

i. said first element consists essentially of zinc sulfide;

ii. said second element consists essentially of zinc selenide; and

the second geometry of the first element and the third geometry of the second element form an interface.

3. A multi element apparatus as set forth in claim 1, wherein:

i. said first element consists essentially of zinc selenide;

ii. said second element consists essentially of zinc sulfide; and

the second surface geometry of the first element and the first surface geometry of the second element form an interface.

4. A multi element apparatus as set forth in claim 1, wherein the second surface geometry of the first element and the third surface geometry of the second element are spaced a variable distance apart, wherein said distance is selected to optimize the multiple waveband focusing properties of the apparatus.

5. A multi element apparatus as set forth in claim 1, wherein the apparatus possesses a 30-cm aperture and approximately a 71-cm focal length in both bands.

6. A multi element apparatus as set forth in claim 1, wherein said apparatus comprises:

i. a first element consisting essentially of Zinc Selenide and having an index of refraction of approximately 2.43 of millimeter wave radiation and approximately 3.01 for infrared radiation;

ii. a second element having an index of refraction of approximately 2.25 for millimeter wave radiation and approximately 2.90 for infrared radiation; and

iii. wherein the second surface geometry of the first element and the first surface geometry of the second element possess substantially identical but inverted geometries and conform with each other to produce an interface between said second surface geometry o the first element and the third surface geometry of the second element and

iv. wherein the first element has an aperture of about 30-cm and a focal length of about 71-cm focal length for both millimeter wave and infrared radiation.

7. A multi element lens capable of simultaneously focusing on a plurality of wavebands in substantially the same focal plane, comprising:

i. a first element comprising a first composition and having a first thickness, a first perimeter, a first index of refraction unique to the waveband passing though the element, and a first and second surface substantially perpendicular to said perimeter wherein said first surface has a first radius and wherein said second surface has a second radius;

ii. a second element comprising a second composition and having a second thickness, a second perimeter, a second index of refraction unique to the waveband passing though the element, and a first and second surface substantially perpendicular to said perimeter wherein said first surface has a third radius and wherein said second surface has a fourth radius; and

iii. said first and second elements are aligned such that the second surface of the first element and the first surface of the second element are in substantial conformity with each other and aligned such that the perimeters essentially form a column; and

wherein

a. said first radius is a negative 54 cm;

b. said second radius is a positive 24 cm;

c. said third radius is a negative 42.9 cm;

d. said fourth radius is a positive 29.94 cm;

e. said first index of refraction is 2.3 for infrared radiation and 2.9 in for mm-wave radiation;

f. said second index of refraction is 2.4 for infrared radiation and 3.0 for mm-wave radiation.