  We experimentally show that indirect light-induced electron transitions could
lead to THz detection on standard CCD and CMOS sensors, introducing this
well-established technological concept to the THz range. Unlike its optical
counterpart, we found that the THz sensitivity is nonlinear. We imaged 1-13 THz
radiation with photon energy less than 2% of the well-established band gap
energy threshold. The unprecedented small pitch and large number of pixels
uniquely allowed us to visualize the complex propagation of THz radiation, as
it focuses down to the physical diffraction limit. Broadband pulses were
detectable at a single shot. This opens a whole new field of real time THz
imaging at the frame rate of the sensor.
