Miniature photoconducting capacitor array as a source for tunable THz radiation

The prospects of a miniature photoconducting capacitor array as a source for THz radiation are discussed. The device consists of an alternately biased capacitor array built on a semiconductor substrate and illuminated by a short laser pulse. The laser pulse creates a propagating plasma front inside the crystal volume by side illumination, and triggers the discharging of the capacitor by shorting out the photoconducting material between each capacitor plate. The sequential discharge of the capacitor array inside the expending plasma region can be considered as an interaction between a static wave and a superluminous ionizing front. In the present article we have demonstrated production of two cycle pulses with a center frequency of up to 1.5 THz. The device combines elements from the well-known "frozen-wave" generator and from the photoconducting switches array. The underlying physics of this radiation mechanism is very similar to the dc-to-ac conversion mechanism inside a gas-filled capacitor array which generates coherent microwave radiation.