Single-shot time-domain imaging of terahertz pulses via nonlinear optical frequency mixing

We demonstrate a single-shot temporal imaging technique for terahertz (THz) waves based on spatially resolved nonlinear frequency mixing. By employing sum or difference frequency generation (SFG or DFG) in a non-collinear geometry, our method maps the temporal evolution of a THz field into a spatially encoded near-infrared (NIR) signal. The angular separation of the generated NIR photons, governed by phase-matching conditions, enables the time-dependent THz waveform to be mapped directly onto a camera without the need for mechanical time-delay scanning. Using an intense THz source, this approach achieves a signal-to-noise ratio (SNR) comparable to conventional electro-optical sampling after scanning millions of laser pulses, but all at once. This method requires no modification to the probing light, such as spectral chirping, making it ideal for dynamic, nonlinear, non-repetitive processes. It provides real-time, high-resolution access to ultrafast THz dynamics in single-shot interactions, operating at the laser repetition rate and limited only by the acquisition speed of the line-scan camera. These results pave the way for advanced THz diagnostics in experimental setups where scanning is impractical or real-time access is mandatory.