Functionalization of THz quantum cascade lasers

Laser action is normally initiated by the amplification of spontaneous emission. As spontaneous emission is a random process, the carrier phase of a laser is different each time a laser is turned on. As a consequence, it is not possible to measure the time-resolved electric field of a free-running terahertz (THz) laser using standard coherent detection techniques (such as electro-optic or phoconductive sampling).