Abstract: Apparatus and methods for characterizing free-space electromagnetic energy, and in particular, apparatus/method suitable for real-time two-dimensional far-infrared imaging applications are presented. The sensing technique is based on a non-linear coupling between a low-frequency electric field and a laser beam in an electro-optic crystal. In addition to a pratical counter-propagating sensing technique, a co-linear approach is described which provides longer radiated field--optical beam interaction length, thereby making imaging applications practical.

Abstract: A source of collimated beam or beams of microwave electromagnetic radiation pulses comprises a photoconductor substrate having a major surface and an optical radiation source providing a beam of optical radiation pulses for illuminating at least a relatively large aperture region of the major surface. A static electric field, intrinsic or applied, is present at the major surface for driving transient photocurrents generated by the beam of optical radiation pulses. Each beam of microwave electromagnetic radiation pulses emitted from the photoconductor substrate may be steered by varying the angle of incidence of the beam of optical radiation pulses illuminating the major surface, by varying the period of the spatial variation of a static electric field applied to the major surface by means of electrodes, or by varying the period or direction of a periodic intensity variation of a spatially modulated beam of optical radiation pulses on the major surface.