Single-shot ultrabroadband coherent detection of high-energy THz pulses

We present a single-shot, ultrabroadband coherent detection scheme capable of resolving millijoule-class, inherently broadband terahertz (THz) waveforms from low-repetition-rate, high-energy laser systems. The technique integrates scanning-free solid-state biased coherent detection with a non-collinear probe-THz geometry and a balanced detection scheme based on orthogonal polarization states of the THz and bias fields. This configuration enables effective suppression of incoherent background and allows extraction of the THz electric field from a single laser pulse. A line-focused overlap between a femtosecond optical probe and a focused THz beam within a 1-μ m-thick silicon nitride detector yields a tunable ∼ ps time window with few-fs time resolution, limited only by the optical probe duration and camera pixel size. We demonstrate the method using millijoule-level THz pulses generated by relativistic fs laser interactions with copper foils, achieving single-shot detection of coherent spectral contents exceeding 15 THz. We also examine the impact of imperfect alignment on measurement accuracy and describe procedures for recovering the coherent THz waveforms under partially imbalanced detection conditions. This technique facilitates field-resolved investigations of extreme THz-matter interactions, where both high field strength and broad spectral coverage are essential.