Patent ID: 8481939

Claim:
An apparatus comprising: a generation unit configured to generate excitation light; a power source, and a photoconductive device comprising: a photoconductive layer configured to generate carriers upon irradiation with excitation light; a first electrode arranged on the photoconductive layer; a second electrode arranged on the photoconductive layer with a gap between the first and second electrodes; and a third electrode arranged in a region over which an electric field caused by voltages applied to the first and second electrodes or an electric field caused by irradiation with a terahertz wave extends, wherein a depletion layer of the photoconductive layer is controllable by a voltage applied to the third electrode, wherein a terahertz wave is generated by irradiating the gap between the first and second electrodes with the excitation light in a state where a voltage is applied to the third electrode, the voltage being different from the voltages of the first and second electrodes, and wherein a voltage is applied to the third electrode by the power source.