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.

Ultrafast spectroscopy is a powerful scientific approach that employs ultrashort light pulses—typically ranging from femtoseconds to attoseconds—to investigate photoinduced physical processes in atoms, molecules, nanostructures, and condensed matter systems. By capturing dynamical phenomena on their intrinsic timescales, ultrafast spectroscopy provides direct insight into fundamental processes such as energy transfer, charge separation, and coherent wavepacket evolution. In recent years, rapid advances in ultrashort pulse generation and high-precision detection technologies significantly expanded the capabilities of this field, enabling increasingly sophisticated studies while simultaneously introducing new technical and conceptual challenges.

Ultrafast spectroscopy uniquely resolves transient phenomena that govern microscopic matter behavior. Many key physical, chemical, and biological processes—including electron transfer in photovoltaic materials, bond breaking and formation in chemical reactions, and energy transfer in photosynthesis—occur on femtosecond or even attosecond timescales. Conventional steady-state techniques are incapable of capturing these dynamics, making ultrafast spectroscopy indispensable for uncovering underlying mechanisms.

Moreover, the field plays a crucial role in advancing modern technologies. For example, understanding carrier dynamics in semiconductors directly impacts the design of high-efficiency solar cells and optoelectronic devices. Similarly, probing ultrafast processes in nanostructures and quantum materials provides essential knowledge for next-generation electronics, photonics, and quantum information science. As such, ultrafast spectroscopy not only deepens our fundamental understanding of matter but also drives innovation across a wide range of applied disciplines.

Significant progress was achieved in ultrafast spectroscopy over the past decades, largely driven by breakthroughs in light source development and experimental methodologies. One of the most notable advances was the generation of ultrashort pulses across an extremely broad spectral range, from X-rays to terahertz frequencies. X-ray free-electron lasers and high-harmonic generation sources enabled element-specific and site-selective probing of ultrafast dynamics, while terahertz spectroscopy provided unique access to low energy states like free charge in photovoltaics, phonon polaritons, and collective modes in solids.

Pump–probe techniques remained the cornerstone of ultrafast spectroscopy. By using one pulse to excite the system and another to probe its subsequent evolution, researchers can map out time-resolved dynamics with remarkable precision. These methods were widely applied to study photovoltaic conversion processes under solar-equivalent excitation densities, revealing detailed mechanisms of exciton dissociation, charge transport, and recombination. Similarly, ultrafast pump–probe spectroscopy enabled the investigation of photodecomposition and photochemical reaction pathways, offering real-time observation of intermediate states.

Beyond conventional pump–probe approaches, advanced spectroscopic techniques such as two-dimensional coherent spectroscopy emerged as powerful tools. These methods combined high temporal resolution with high excitation energy resolution, allowing researchers to disentangle complex interactions in multi-level systems. Two-dimensional spectroscopy proved particularly effective in studying coherent coupling, tracking wavepacket dynamics, and extracting higher-order correlation signals that were inaccessible with simpler techniques. This led to important insights into quantum coherence and many-body interactions in both molecular and solid-state systems.

Another major development was the integration of near-field optics with ultrafast spectroscopy. Traditional optical techniques were limited by the diffraction limit, restricting spatial resolution to the micron scale. Near-field approaches overcame this limitation, enabling nanoscale spatial resolution while preserving ultrafast temporal resolution. This combination opened new possibilities for investigating heterogeneous materials, nanostructures, and localized phenomena, such as plasmonic excitations and nanoscale energy transfer processes.

In parallel, advances in detection technologies and precision metrology further enhanced the sensitivity and accuracy of ultrafast measurements. Techniques such as frequency comb spectroscopy and quantum-enhanced detection schemes pushed the limits of measurement precision, enabling the observation of extremely weak signals and subtle dynamical effects. Additionally, the growing intersection between ultrafast spectroscopy and quantum optics introduced new paradigms for controlling and probing quantum states of light and matter.

In summary, ultrafast spectroscopy has evolved into a versatile and indispensable tool for exploring the fundamental dynamics of matter on its natural timescales. The field has witnessed remarkable progress, driven by innovations in light source technology, experimental techniques, and detection methods. From broadband ultrashort pulse generation to multidimensional coherent spectroscopy and near-field integration, these advances have expanded the scope and impact of ultrafast studies.

Looking forward, several challenges and opportunities remain. Achieving simultaneous high temporal, spectral, and spatial resolution continues to be a central goal, requiring further technological breakthroughs. The development of more stable, tunable, and accessible ultrashort pulse sources will be critical for broadening the applicability of ultrafast spectroscopy. In addition, improving detection sensitivity and reducing noise will be essential for studying increasingly complex and weakly interacting systems.

Overall, ultrafast spectroscopy stands at the forefront of modern science, offering unparalleled insights into the dynamic behavior of matter. With continued advancements and interdisciplinary collaboration, it is poised to play an even more significant role in shaping the future of physics, chemistry, and materials science.