Fabry-Perot scanning and nutating imaging coherent radiometer

Apparatus for determining the direction and wavelength of coherent radiation or coherent absence of radiation in the presence of incoherent ambient radiation which comprises:

• a Fabry-Perot etalon having a first surface positioned to receive incoming radiation and a second surface, the distance between said surfaces being such that the optical path difference between the transmitted portions of radiation incident on said first surface is substantially grater than the coherence length of incoherent radiation but substantially less than the coherence length of the coherent radiation;
• means for rotating said etalon an equal amount at different angular velocities about each of two mutually perpendicular axes of rotation;
• position indicating means to provide a position signal proportional to the angle of rotation of said Fabry-Perot etalon about each of said axes of rotation;
• detecting means for detecting the variable signal component caused by the varying constructive and destructive interference of the combined coherent radiation components across the entire area of the wavefront emanating from said Fabry-Perot etalon;
• and
• processing means for processing said position signals and said variable signal components through electronic signal processing components to detect, determine direction and wavelength of the coherent energy or coherent absence of energy.