An in situ single-shot setup for strong-field terahertz pump-terahertz probe spectroscopy

The practical applications of low-repetition-rate high-power terahertz (THz) sources remain challenging, primarily due to the low data acquisition efficiency and shot-to-shot fluctuations. To overcome this challenge, we propose and implement a novel THz pump-THz probe (TPTP) experimental configuration that combines in situ detection with spatially encoded mapping of pump-field-strength dependence. In our TPTP setup, the THz probe beam is larger in size than the pump pulse on the sample, and the spatiotemporal distribution of the THz probe beam that has just passed through the sample is measured directly with the single-shot electro-optic sampling technique. Such an in situ THz probe configuration not only enables truly single-shot measurements by acquiring the probe signals with and without the pump simultaneously but also allows for the single-shot retrieval of the pump-field-dependent THz probe signals at a specific pump-probe delay time. The THz pump-probe spatiotemporal overlap at the sample and the spatially encoded pump field mapping onto the detection crystal are calibrated. A proof-of-concept experiment on the strong THz-field-induced absorption bleaching in silicon is conducted to demonstrate the capability of the platform. Our proposed TPTP setup will greatly improve the acquisition efficiency and signal-to-noise ratio of data, particularly for low-repetition-rate strong-field THz platforms.