Infrared imaging system for advanced rescue vision system

An infrared imaging system including apparatus for mounting on a helmet comprising:

• an infrared camera head mounted on said helmet for converting infrared light images into electronic signals;
• a display unit mounted on said helmet for converting electronic signals into visible light images;
• electronic means coupled between the infrared camera and the display unit, including controller means, for processing video signals from the infrared camera and supplying them to the display unit;
• a combiner mounted on said helmet so that it is in front of the eyes of a user when the helmet is worn, so that the user can directly view an external scene;
• relay optic means mounted on said helmet to couple light images from the display unit to the combiner, whereby the user can view an image from the display unit as well as the external scene;
• wherein said infrared camera comprises camera optics, a chopper, and a detector having a staring focal plane array (FPA), the infrared camera having a waveband of infrared radiation selected to be in a range from 2 μm to 12 μm, the camera optics and detector having an objective lens and detector window which are transparent for said waveband;
• wherein the objective lens comprises first and second lenses separated by an air gap, with first and second faces on the first lens, and third and fourth faces on the second lens, the first lens being constructed by hot pressed CaF2, and the second lens being made of hot pressed ZnS;
• wherein the objective lens is designed with ten basic lens design parameters for this objective lens formed by the combination of two lenses, these parameters being:
• 1. curvature r1 of the first face,
• 2. spacing d1 of the first lens,
• 3. refraction index n1 of the first lens,
• 4. curvature r2 of the second face,
• 5. air gap d2,
• 6. refraction index n2 of the air gap,
• 7. curvature r3 of the third face,
• 8. spacing d3 of the second lens,
• 9. refraction index n3 of the second lens,
• 10. curvature r4 of the fourth face 4,
• these parameters being as shown in the following table:
• Parameter Curvature r Aperture D Spacing d Ref Face Mm Mm mm Index n Material 1 64.50 25 2.31 1.35 CaF2 2 52.00 25 0.51 1.00 Air 3 76.90 25 2.31 2.25 ZnS 4 249.00 25 — — —