J. T. Darrow

Optically steerable photoconducting antennas

When illuminated by ultrashort optical pulses, large aperture planar photoconductors are shown to radiate a directional electromagnetic pulse which can be steered by varying the angle of incidence of the optical beam.

Subpicosecond electromagnetic pulses from large-aperture photoconducting antennas

The radiation efficiency and physical mechanism for the generation of subpicosecond electromagnetic pulses from large-aperture photoconducting antennas are evaluated. The rise time of the photocurrent is found to be more important than the fall time in determining the relative sensitivity of photoconducting materials. Indium phosphide is found to be almost 10 times more sensitive than radiation-damaged silicon-on-sapphire.

Optically induced electromagnetic radiation from semiconductor surfaces

Ultrafast electromagnetic radiation induced by a femtosecond laser beam from a semiconductor provides determination of the impurity doping concentration, carrier mobility, sign, and strength of the depletion field near the semiconductor surface.

Power scaling of large‐aperture photoconducting antennas

We describe the power scaling and saturation properties of large‐aperture planar photoconducting antennas which emit and detect ultrashort terahertz electromagnetic pulses. At high optical fluences, the radiated electric field saturates at a value comparable to the bias field in agreement with a simple model of the radiation mechanism.

Large-aperture photoconducting antennas excited by high optical fluences

The saturation and power scaling of terahertz radiation produced by large-aperture photoconducting antennas under high electric fields and high optical fluences are described. From the saturation behavior, a large-aperture transmitter can be designed to produce the maximum pulse energy of terahertz radiation for a given photoconductor, optical pulse energy and electric field.

Optically Induced Femtosecond Electromagnetic Radiation from Semiconductor Surfaces

Terahertz bandwidth electromagnetic radiation can be optically induced from semiconductor surfaces [1]. This diffraction-limited electromagnetic beam propagates in free space and can be optically steered by varying the incident angle of the laser beam. In addition, from the analysis of measured waveforms of the radiated field, the impurity concentration, carrier mobility, crystal symmetry, orientation and strength of the built-in field near the semiconductor surfaces can be estimated with a noncontact approach [2].