The gating time of conventional electro-optical switches is on the order of several nanoseconds and is limited by the response time of the Pockels effect. To achieve a gating time on the femtosecond timescale, Mostafa Shalaby and co-workers from Switzerland have now developed a diamond-based terahertz (THz)-driven optical modulator, using a thin disk of diamond (0.5 mm thick, 4.5 mm diameter). Intense THz pulses (field strength of 83 MV cm−1 with a spectral peak at 3.5 THz) from the Swiss free-electron laser facility were sent through the diamond disk collinearly with infrared 50-fs pulses centred at 800 nm. The phase retardation of the 800-nm pulse induced by the Kerr nonlinearity was proportional to the THz peak intensity. A polarizer was used to filter out the polarization of the switched pulse. Gating with a time response of 125 fs was obtained. This gating technique was also employed to perform 3D imaging of THz pulses. The 2D intensity profiles of the THz pulse were measured by a CCD sensor as a function of the delay time between the THz pulse and the 800-nm pulse. The reconstructed 3D pulse resembled a cigar-like shape.