Coherent light source detector

Claim 2

Apparatus for detecting a source of coherent radiation in the presence of non-coherent ambient radiation comprising: an unequal optical path length interferometer of the type in which portions of the radiation impinging on the interferometric component are caused to be recombined after travelling two different optical paths; said optical paths differing in length by an amount substantially greater than the coherence length of the noncoherent radiation by substantially less than the coherence length of the coherent radiation; means for detecting the intensity of said recombined portions and producing a signal representative thereof; and means for varying the effective difference in length between said two optical paths; said optical path length varying means being of such construction as to vary said effective optical path length difference in a known systematic manner, so that said detecting means produces a variable signal component caused by the varying constructive and destructive interference of the recombined coherent radiation components, while the recombined non-coherent radiation components produce only a steady background signal; said unequal optical path length interferometric component comprising a Fabry-Perot etalon; and said optical path varying means comprising means for continuous tilting said Fabry-Perot etalon through an angular range including a zero angle of incidence of the coherent radiation relative to said etalon, whereby said variable signal component is of almost periodic form but of gradually increasing frequency as the impinging coherent radiation makes an increasing angle of incidence relative to said etalon and said variable signal component includes a distinct form of minimum frequency corresponding to said zero angle of incidence, so that the direction of said coherent radiation source may be readily determined.

Claim 3

Apparatus according to claim 1, in which: said tilting means is capable of constantly tilting said Fabry-Perot etalon in a linearly changing manner, so that the angle of incidence of said coherent radiation relative to said etalon also changes in such a linear manner, whereby said almost periodic variable signal component has a period at any given interval which is proportional to the wavelength of said coherent source, so that said wavelength may also be readily determined.

Claim 4

Apparatus for detecting a source of coherent radiation in the presence of non-coherent ambient radiation comprising: an unequal optical path length interferometer of the type in which portions of the radiation impinging on the interferometric component are caused to be recombined after travelling two different optical paths; said optical paths differing in length by an amount substantially greater than the coherence length of the non-coherent radiation but substantially less than the coherence length of the coherent radiation; means for detecting the intensity of said recombined portions and producing a signal representative thereof; and means for varying the effective difference in length between said two optical paths; said optical path length varying means being of such construction as to vary said effective optical path length difference in a known systematic manner, so that said detecting means produces a variable signal component caused by the varying constructive and destructive interference of the recombined coherent radiation components, while the recombined non-coherent radiation components produce only a steady background signal; said unequal optical path length interferometric component comprising a Fabry-PeroT etalon; and said optical path length varying means comprising means for constant tilting of said Fabry-Perot etalon; so that said variable signal component is of almost periodic form but of gradually increasing frequency as the impinging coherent radiation makes an increasing angle of incidence relative to said etalon; said Fabry-Perot etalon comprising two portions mutually varying in spacing between the partially reflecting surfaces by a distance equal to an odd multiple of a quarter of a wave-length of the coherent radiation; said detecting means comprising means for separately detecting the individual intensity of the radiation passing through each of said etalon portions and producing a separate signal representative of each said individual intensity; and means for effectively subtracting said separate signals; whereby any steady background signal components caused by non-coherent radiation in said separate signals are substantially eliminated from the resulting difference signal, while the variable signal components caused by the coherent radiation are effectively added.

Claim 5

Apparatus for detecting a source of coherent radiation in the presence of non-coherent ambient radiation comprising: an unequal optical path length interferometer of the type in which portions of the radiation impinging on the interferometric component are caused to be recombined after travelling two different optical paths; said optical paths differing in length by an amount substantially greater than the coherence length of the non-coherent radiation but substantially less than the coherence length of the coherent radiation; means for detecting the intensity of said recombined portions and producing a signal representative thereof; and means for varying the effective difference in length between said two optical paths; said optical path length varying means being of such construction as to vary said effective optical path length difference in a known systematic manner, so that said detecting means produces a variable signal component caused by the varying constructive and destructive interference of the recombined coherent radiation components, while the recombined non-coherent radiation components produce only a steady background signal; said unequal optical path length interferometric component comprising a Fabry-PeroT etalon; and said optical path length varying means comprising means for constant tilting of said Fabry-Perot etalon; so that said variable signal component is of almost periodic form but of gradually increasing frequency as the impinging coherent radiation makes an increasing angle of incidence relative to said etalon; said Fabry-Perot etalon comprising two portions mutually varying in spacing between the partially reflecting surfaces by a distance equal to an odd multiple of a quarter of a wave-length of the coherent radiation; said detecting means comprising means for separately detecting the individual intensity of the radiation passing through each of said etalon portions and producing a separate signal representative of each said individual intensity; and means for effectively subtracting said separate signals; whereby any steady background signal components caused by non-coherent radiation in said separate signals are substantially eliminated from the resulting difference signal, while the variable signal components caused by the coherent radiation are effectively added.