Abstract: A radiation field analyzer (10) provides means for analyzing the spatial mode spectrum of radiation received from a scene. In a multimode waveguide embodiment, light from a laser (24) is directed towards a scene through an alumina waveguide structure (12). A portion of the laser light is directed towards a mode generator (28) which selectively converts the laser radiation into one of a series of modes. Laser light returning from the scene is mixed with the light from the mode generator to produce interference signals. These signals are measured by a detector (34) and analyzed by a programmed computer (36). By sequentially altering the mode generated by the generator (28) and analyzing the resulting signals, a spectrum of the modes returning from the scene is obtained.