COVERT ILLUMINATION
First Claim
1. A method of covert illumination comprising providing an optical source having an optical output tuned to an absorption wavelength of atmospheric oxygen, and illuminating the scene with said optical source.
1 Assignment
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Accused Products
Abstract
This invention relates to methods and apparatus for covert illumination. The method involves illuminating the scene with light which is tuned to an absorption resonances of atmospheric oxygen gas. Light tuned to have a wavelength corresponding to an oxygen absorption wavelength travelling through the atmosphere is therefore attenuated by absorption. The method therefore teaches that a low power illumination source can be used to illuminate nearby objects, thus allowing the detail thereof to be resolved, and the illuminating light reflected from the object, or even the light source itself, will be undetectable beyond a certain range due to atmospheric absorption. The illumination may be used in conjunction with the use of low light level imagers to image a scene. Alternatively the illumination could be used for short range optical communication which will be undetectable at much longer range.
30 Citations
27 Claims
- 1. A method of covert illumination comprising providing an optical source having an optical output tuned to an absorption wavelength of atmospheric oxygen, and illuminating the scene with said optical source.
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19. A method of covert low light level imaging comprising illuminating a scene with an optical source having an optical output tuned an absorption wavelength of atmospheric oxygen and imaging the scene with a low light level imager responsive to the wavelength of illumination.
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- 21. An optical source tuned to an atmospheric absorption wavelength comprising a laser having a feedback control means for wavelength locking the laser output to the atmospheric absorption wavelength, wherein the feedback control means passes at least some of the laser output through a sample of the target atmospheric constituent and analyses the intensity thereof and wherein the target atmospheric constituent is held within a photonic bandgap fibre which is transmissive at the atmospheric absorption wavelength.
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Specification