【摘要】 空气等离子体与太赫兹波的相互作用主要被用于实现太赫兹脉冲相干探测和超快动力学探测。空气等离子体由短脉冲激光放电产生，它是一种复杂的物质形态，其参数随着时间变化而不断变化。用太赫兹脉冲检测空气等离子体可以获取皮秒时间尺度上自由电子动力学的重要信息，这是其他方法无法实现的。相比于固体介质，气体没有损伤阈值，并且具有持续再生能力，这些特性使得气体能够探测覆盖整个太赫兹频谱的超宽带太赫兹脉冲。本文介绍了空气等离子体与太赫兹波相互作用的相关研究进展，重点介绍了太赫兹电场诱导的二次谐波对太赫兹波的相干探测、太赫兹波增强等离子体的声波和荧光发射，以及等离子体的超快动力学探测等，旨在为相关领域的研究人员提供参考。更多还原

【Abstract】 Significance Terahertz(THz) wave refers to the electromagnetic wave with frequencies ranging from 0.1 to 10 THz(wavelengths of 3000 to 30 μm). THz frequency band covers the characteristic spectra of materials such as semiconductors, organic compounds, and biomolecules. THz technology enhances our understanding of fundamental scientific issues in physics, chemistry, astronomy, informatics, and life sciences, which has various applications spanning radar systems, remote sensing, homeland security and counterterrorism operations, atmospheric and environmental monitoring, real-time biometric analysis, and medical diagnostics.Laser-induced plasma, characterized by transient dynamics and rapid parameter evolution(e. g., picosecond-scale variations in density, temperature, and pressure), plays a pivotal role in molecular dissociation, high-harmonic generation, and atmospheric remote sensing. Conventional diagnostic techniques, such as Langmuir probes, optical emission spectroscopy, and microwave interferometry, are limited by insufficient spatial resolution for capturing ultrafast plasma processes. In contrast, THz radiation offers distinct advantages for non-invasive plasma characterization due to its low photon energy, broadband spectral coverage, and intrinsic picosecond-scale pulse duration. Despite these advantages, the acoustic and fluorescence properties of laser-induced plasma under THz pulse excitation are not fully understood, especially the temporal evolution of the plasma’s temperature and density under the action of THz wave. Moreover, owing to their distinctive characteristics, including the absence of phonons and dispersion, damage threshold-free operation, and continuous regeneration capability, gaseous media have emerged as promising candidates for THz sensors.In the past few years, a series of innovative experiments and simulations have been conducted regarding the ultrafast dynamic evolution of key parameters in air plasma, including the optoacoustic properties, temperature, and electron density. Researchers have mainly employed two indirect detection methodologies, namely terahertz radiation-enhanced fluorescence emission(THz-REEF) and terahertz-enhanced acoustics(TEA), to detect THz wave through measurements of laser-induced air plasma fluorescence and acoustic pressure emissions. In particular, the strong THz-field-enhanced fluorescence emission generated by excited nitrogen molecules serves as a novel tool for simultaneously probing the complex dynamics of plasma density and electron temperature. Two distinct electron relaxation processes were observed in air plasma, interpreted as a competition between the excitation of a triplet state by laser or THzfield-heated electrons and the dissociative recombination of nitrogen molecular ions. Theoretical simulations attribute the relaxation process on the tens-of-picosecond scale to ultrafast temperature decrease, while the longer relaxation spanning hundreds of picoseconds stems from electron density decay. The revealed temporal relaxation dynamics of electron density and temperature under intense THz field provide new insights into laser-air plasma interactions and will advance the engineered implementation of this unique light source.Progress This article reviews recent research progress on the interaction between THz waves and plasma. Notably, THz-wave coherent detection technology, based on second-harmonic generation induced by THz field, provides an experimental foundation for investigating ultrafast dynamics in air plasma. Additionally, THz-enhanced acoustics and THz-radiation-enhanced fluorescence emission offer a methodological framework for the coherent detection of THz pulses(Fig. 5). Both acoustic and fluorescence enhancements exhibit a quadratic dependence on THz field strength(Fig. 4, Fig. 8(c)). The photoionization rate varies with laser polarization states, with circularly polarized light yielding a lower rate than linearly polarized light. Consequently, this difference influences the population of free electrons and their kinetic energy, thereby modulating the maximal acoustic and fluorescence emissions(Fig. 6, Fig. 12). The temporal evolution of fluorescence can be described by a biexponential decay model under strong THz field illumination. The first decay component, which corresponds to a lifetime of several hundred picoseconds, can be attributed to the decline in free-electron density, which scales with increasing laser energy and air pressure. A second decay component with shorter relaxation time(～20 ps) emerges when the laser energy exceeds 150 μJ or the air pressure surpasses 410 mbar(Figs. 11(d), 11(e)). Furthermore, transient properties of gas plasma, such as electron density and temperature dynamics, have been theoretically simulated using ionization-induced electron drift and collision-driven fluorescence emission(Figs. 11(f), 13). These findings furnish critical parameters for understanding plasma-THz wave interactions and underscore the potential of THz wave in probing plasma molecular dynamics.Conclusions and Prospects The coherent detection of THz wave and the investigation of ultrafast molecular dynamics in air plasma offer a unique perspective for understanding THz-air plasma interactions. Future research will focus on elucidating the excitation and ionization processes within filamentary structures. Based on the existing theoretical models, the dynamics evolution process of particles in air plasma can be further combined, coupling the temperatures and velocities of electrons, ions and excited-state nitrogen molecules to the densities of electrons and molecules, to more accurately describe the particle evolution dynamics process induced by laser and THz field in nitrogen gas. In experimental research, we aim to further clarify the mechanism of THz fluorescence enhancement. Additionally, we will conduct systematic studies on the electron collision dynamics in nitrogen plasma under different pressures and laser pulse energy conditions. In terms of applications, we will achieve higher-sensitivity THz detection. Moreover, combining THz wave and bioacoustic spectroscopy technology can help further expand the application scope of air plasma and THz wave interaction, with potential application prospects. This work aims to deepen the understanding of the underlying physical mechanisms governing the interplay among air plasma, laser pulse, and THz wave. Such advancements are expected to drive progress in related fields, including plasma diagnostics, ultrafast photoluminescence modulation and remote sensing.更多还原