Demonstration of submillimeter radiation generation from static field by superluminous ionization front in semiconductor capacitor array

Generation of frequency upshifted monochromatic radiation in the 100 GHz to FIR range by the interaction of a superluminous photoconducting front with an electrostatic "frozen wave" configuration in a semiconductor is reported. The interaction converts the energy contained in the "frozen wave" into monochromatic radiation, whose frequency depends on the energy in the laser pulse creating the superluminous front and the wavelength of the static wave. Monochromatic free space propagating waves with frequency between 100 GHz and 1.6 THz were generated using a 100 fsec Ti:sapphire laser pulse incident obliquely on a ZnSe photoconducting slab containing a frozen wave field. A superluminous photoconducting front was formed by two photon absorption. Tunability was achieved by varying the laser pulse energy from .1 to 1 mJ. The electric field waveform of the emitted radiation pulse was measured by an optically gated miniature dipole antenna. The concept can be scaled to develop narrowband, tunable and powerful THz and FIR sources for spectroscopic imaging and other applications.