Glint responsive parametric amplified phase conjugate signal laser radar

Abstract

A laser radar system in which a laser beam is used to illuminate a target region of interest. The density of the laser radiation at the target plane is low enough that the reflected energy from diffusing portions of the target is not detectable by the laser radar receiver. Target reflections from retroreflective portions of the target such as glint signal reflections are also not initially detectable by the radar however these reflections are of such greater signal strength that the radar system is arranged to respond to the glint signals after they are enhanced by optical processing which includes re-illumination of the target glint area by a phase conjugated and parametrically amplified enhancement of the original reflected glint signal. Plural uses and alternate arrangements of the invention are included.

What is claimed is: 
     
       1. Glint responsive laser radar apparatus comprising the combination of: a laser source of optical energy capable of illuminating a distal target;   optical energy image reception apparatus capable of detecting at least a glint signal return from said laser illuminated distal target;   optical signal amplification apparatus connected with a glint signal related output signal of frequency ω 1  at an output port of said optical energy image reception apparatus and having a pump signal of frequency ω 3 , and an output signal path idler frequency of ω 2  ;   optical phase conjugation apparatus connected with said ω 2  idler frequency output signal path of said optical signal amplification apparatus and generating a backward propagating complex conjugate wave of said ω 2  idler frequency along said ω 2  signal path;   means for communicating said backward propagating complex conjugate wave of ω 2  idler frequency back to said laser illuminated distal target in secondary reflection supplemental enhancement of said target illumination and said glint signal return therefrom;   an operator viewable optical receiver output display responsive to receipt of signals representing said glint signal from said optical phase conjugation apparatus.   
     
     
       2. The glint responsive laser radar apparatus of claim 1 wherein said optical energy image reception apparatus includes a detection threshold capable of discriminating between higher amplitude reflected optical signals including said glint signal and other lower amplitude signals received from said distal target. 
     
     
       3. The glint responsive laser radar apparatus of claim 1 wherein said optical signal amplification apparatus comprises one of a parametric amplification three wave mixing apparatus, a four wave mixing Stimulated Raman device and a four wave mixing Stimulated Brillouin device. 
     
     
       4. The glint responsive laser radar apparatus of claim 1 wherein said optical signal amplification apparatus comprises a parametric amplification three wave mixing apparatus. 
     
     
       5. The glint responsive laser radar apparatus of claim 1 wherein said operator viewable optical receiver output display also includes one of an Infra Red camera and a focal plane electro-optic detector array. 
     
     
       6. The glint responsive laser radar apparatus of claim 1 wherein said apparatus comprises a portion of an airborne weapons guidance apparatus. 
     
     
       7. The glint responsive laser radar apparatus of claim 1 wherein said apparatus comprises a portion of an unmanned aircraft landing operation apparatus. 
     
     
       8. The glint responsive laser radar apparatus of claim 1 wherein said optical energy image reception apparatus and said optical signal amplification apparatus include input and output optical lens apparatus respectively. 
     
     
       9. The glint responsive laser radar apparatus of claim 1 wherein said distal target comprises one of a man made object and a naturally existing object. 
     
     
       10. The method of operating a highly directional laser radar system comprising the steps of: illuminating a distant target with laser based optical energy;   communicating an optical signal return from both a signal diffusing area and a glint element of said distant target to an optical receiver apparatus;   generating, in an optical amplifier of selected high threshold response, an amplified output signal representation of a glint element-determined input signal from said optical receiver apparatus, said generating step including forming, in said selected high threshold optical amplifier, input frequency and output frequency-related different frequency signals;   forming from said amplified output signal a phase conjugated signal representative of said glint element signal;   communicating said phase conjugated signal in opposed direction through said amplifier to form a reamplified phase conjugate signal;   enhancing said optical signal return from said distant target by additionally illuminating said target with said reamplified phase conjugate signal;   communicating a representation of said input signal as enhanced by said additional illumination to a using apparatus.   
     
     
       11. The method of operating a highly directional laser radar system of claim 10 wherein said laser based optical energy is monochromatic in nature. 
     
     
       12. The method of operating a highly directional laser radar system of claim 10 wherein said step of communicating a representation of said enhanced input signal includes one of the steps of communicating said signal to an operator by displaying a resulting signal on a viewable display and communicating said signal to one of an Infra Red camera and a focal plane electro-optic detector array. 
     
     
       13. The method of operating a highly directional laser radar system of claim 10 wherein said step of communicating a representation of said enhanced input signal includes each of the steps of communicating said signal to an operator by displaying a resulting signal on a viewable display and communicating said signal to an Infra Red camera and a focal plane electro optic detector array. 
     
     
       14. The method of operating a highly directional laser radar system of claim 10 wherein said step of forming an amplified output signal in an optical amplifier of selected high threshold response includes processing said amplified output signal in a parametric amplifier apparatus. 
     
     
       15. The method of operating a highly directional laser radar system of claim 10 wherein said step of forming an amplified output signal in an optical amplifier of selected high threshold response includes processing said amplified output signal in one of a four wave mixing Stimulated Raman amplifier and a four wave mixing Stimulated Brillouin amplifier. 
     
     
       16. The method of operating a highly directional laser radar system of claim 10 wherein said steps of generating, forming from said amplified output signal, communicating said phase conjugated signal, and enhancing by additionally illuminating are repeated in a continuing plurality of illumination-increasing iterations for each distant target object.