Wide angle, narrow bandwidth laser detection system

Claim 1

A detection system for examining a large field of view to determine if the detection system is being illuminated by radiation at a specific frequency, and comprising: a. a detector means responsive to radiation at said specific frequency for producing a signal when the detector means is illuminated by radiation at said specific frequency; b. an optical system for passing nonimaged radiation received over the field of view and in a predetermined narrow band pass region around said specific frequency to said detector means, and for forming an image of said detector means at the entrance aperture of the optical system, and including: i. an interference filter means for allowing radiation in said predetermined naroow narrow pass region about said specific frequency to be passed to said detector means, said interference filter means having the characteristic of shifting its band pass region for radiation not received at angles substantially perpendicular to the interference filter means, whereby it is necessary to substantially collimate the radiation received over the large field of view and pass it through said interference filter means at substantially perpendicular angles; ii. a first positive lens system for receiving radiation from over the large field of view and for substantially collimating the radiation for telecentric passage through said interference filter means, said first positive lens system including a first fresnel lens in juxtaposition with said interference filter means, and a first hyperhemispherical lens in juxtaposition with said first fresnel lens with its hyperhemispherical surface facing said first fresnel lens such that radiation from the field of view is received by said first hyperhemishperical lens, passed by said first hyperhemispherical lens to said first fresnel lens, and then passed by said first fresnel lens to said interference filter means; and iii. a second positive lens system for receiving radiation passed by said filter means and for condensing it and directing it onto said detector means, said second positive lens system including a second fresnel lens in juxtaposition with said interference filter means, and a second hyperhemispherical lens in juxtaposition with said second fresnel lens and said detector means with its hyperhemispherical surface facing said second fresnel lens such that radiation is passed by said interference filter means to said second fresnel lens, passed by said second fresnel lens to said second hyperhemispherical lens, and then passed by said second hyperhemispherical lens to said detector means.