THz single-shot optical imaging with tunable time interval

Single-shot multi-frame ultrafast optical imaging is a powerful tool for probing transient phenomena. However, in many ultrafast processes, the rate of temporal evolution varies with time, making conventional equal-interval imaging face a trade-off between temporal resolution and observation window. Here, by utilizing the wavelength-time duality of ultrashort pulses established by optical time-stretch, we generate a pulse sequence with arbitrarily tunable time intervals through spectral modulation. This enables adaptive sampling, i.e., dense sampling for high-dynamic stages and sparse sampling for slow evolution. The observation of laser filament dynamics in air shows that the system achieves 10-frame single-shot imaging with adjustable frame intervals from 0.26 ps to 2.12 ps. We expect that the proposed method can be readily incorporated into a wide spectrum of single-shot multi-frame ultrafast imaging systems, thereby advancing our capability to probe ultrafast phenomena.