Coherent light modulation and detector

Apparatus for detecting the presence of coherent radiation within a field of view of the apparatus, comprising:

• an interferometer including;
• a body of piezoelectric crystalline material substantially transparent to the wavelength of said light beams, and bounded by spaced parallel faces having a spacing of less than about one-forth coherence length of said coherent light beam to be modulated in the material of said body,
• said body being constructed of a material exhibiting a piezoelectric resonance when excited by an time varying electric field of predetermined frequency established between said faces;
• first and second conductive electrodes formed in contact with each said face respectively for forming a pair of conductive electrodes,
• each of said electrodes being internally reflective for said light beams to form an acousto-optic Fabry-Perot interferometer,
• at least one of said electrodes being semitransparent for admission of said light beams into the body of said interferometer and for allowing modulated light to exit after interference so that a coherent light beam admitted into said interferometer undergoes constructive and destructive interference therein;
• means for generating an electrical signal at said predetermined frequency of said body and for connecting said signal to said electrodes for causing piezoelectric expansion and contraction of said body and a corresponding change in separation of said reflective electrodes,
• said electric signal causing an electrical field which expands and contracts said body and electrode reflectors between greater values and lesser values of interference so as to modulate the intensity of said exiting beam with said resonance frequency;
• detector means positioned for receiving the emitted radiation including the intensity modulated coherent radiation, the detector means having an output signal expressive of the intensity of the emitted coherent radiation;
• and
• processing means coupled to the detector means output signal and responsive thereto for indicating when a modulator radiation is received by the detector means.