Design and application of high-speed and high-precision single terahertz detection sensor

Single-shot terahertz time-domain spectroscopy (THz-TDS) encodes temporal delay information into the spatial or spectral domain of a single probe pulse, enabling the acquisition of a complete THz waveform in a single exposure and thereby significantly improving measurement efficiency. However, existing single-shot implementations are limited in accuracy by detector constraints—particularly by the limited full-well capacity and low frame/line rates. Therefore, improving detector performance (e.g., adopting larger full-well capacity and higher frame/line rates), is essential for enhancing single-shot detection accuracy. This work aims to identify the dominant noise mechanisms in single-shot THz detection and to develop a dedicated sensor and detection system capable of achieving higher detection precision.

A spatially encoded single-shot THz detection setup was constructed using an echelon (step-mirror) scheme to map temporal delays onto spatial positions of the probe beam, employing a balanced dual-line complementary metal oxide semiconductor (CMOS) line sensor as the detection unit. This successfully correlated the spatial position with THz temporal delay. Then, a balanced detection scheme with a quarter-wave plate and Wollaston prism was used to convert polarization modulation induced by the THz field into intensity differences. The hardware development included the selection of a high full-well capacity line sensor (FWC = 25.4 Me^-), the design of low-noise front-end analog electronics (voltage follower, differential amplification, and low-pass filtering), and the integration of an FPGA-based timing control and data acquisition platform. A 16-bit analog-to-digital converter (ADC) operating at up to 80 MHz was used for digitization, and 800 ns programmable integration windows were implemented to control effective exposure and suppress dark-current noise. The system performance was evaluated by comparing single-shot reconstructions with conventional step-scan measurements, and by analyzing noise dependence on probe intensity, detector full-well capacity, frame/line rate, and number of averaged pulses. The noise components were separated into readout (intensity-independent) and shot noise (proportional to the square root of intensity), providing quantitative insight for detector and system optimization.

The single-shot reconstructions reproduced both the temporal and spectral features of conventional step-scan results after spatial-to-temporal calibration. A scaling factor of 0.015 ps/pixel was determined for the spatial-to-temporal conversion, and the reconstructed waveforms showed excellent agreement with step-scan data in both time and frequency domains. Noise analysis reveals two regimes: at low probe intensities, the system noise is dominated by intensity-independent readout noise, whereas at higher probe intensities, shot noise dominates and scales with the square root of intensity. Using a large-full-well detector and a low-noise readout circuit, the system achieves a dynamic range of 74 dB and a readout noise of ~ 0.43 mV RMS. Operating at a 5 kHz repetition rate with pulse averaging, the minimum detectable THz field within a 1 s measurement was determined to be about 2.55 × 10^-4 kV/cm. Compared with single-point (step-scan) detection, the developed single-shot system reduces measurement time by approximately 30 times while maintaining equivalent information content.

The results demonstrate that combining a high full-well capacity line sensor, balanced dual-line detection, and system-level low-noise analog/digital design can significantly enhance both the accuracy and efficiency of a single-shot THz-TDS system. Increasing the allowable probe intensity through larger full-well capacity effectively suppresses the relative contribution of shot noise, and serves as a key strategy for improving measurement precision. High line-rate acquisition further reduces random noise, making the proposed approach suitable for rapid and high-precision THz time-domain measurements and providing a solid technical foundation for fast multidimensional THz spectroscopy experiments. This study implies that detector full-well capacity is the critical parameter limiting single-shot THz-TDS precision under typical high-intensity probe conditions, and that the developed sensor and system optimization strategy effectively addresses this bottleneck, enabling high-speed, high-precision measurements crucial for complicated experiments, such as optical-pump THz-probe and 2D THz spectroscopy.