Abstract: A method and apparatus for measuring electromagnetic pulses as a function of time. Radiation measurement, including measurement of single-shot, free-space terahertz femtosecond pulses, is realized using an electro-optical modulator in combination with an optical streak camera. This method and apparatus allow measurement of electromagnetic pulses previously unmeasurable due to the time resolution restrictions dictated by the time-frequency correlation.

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 (or magnetic) field and a laser beam in an electro-optic (or magnetic-optic) crystal. In addition to a practical 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 non-contact method for determining the index of refraction or dielectric constant of a thin film on a substrate at a desired frequency in the GHz to THz range having a corresponding wavelength larger than the thickness of the thin film (which may be only a few microns). The method comprises impinging the desired-frequency beam in free space upon the thin film on the substrate and measuring the measured phase change and the measured field reflectance from the reflected beam for a plurality of incident angles over a range of angles that includes the Brewster's angle for the thin film. The index of refraction for the thin film is determined by applying Fresnel equations to iteratively calculate a calculated phase change and a calculated field reflectance at each of the plurality of incident angles, and selecting the index of refraction that provides the best mathematical curve fit with both the dataset of measured phase changes and the dataset of measured field reflectances for each incident angle.

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.