超宽带太赫兹矢量波形调控机理与实验研究

Terahertz (THz) spectroscopy is of enormous interest for a variety of promising applications in the fields of biology, medicine, chemistry, agriculture, high-speed communication and so on. In the process of applying terahertz spectroscopy, it has been found that the development of high-power broadband terahertz sources is one of the most important problems in the application of this technique. Two-color femtosecond laser (800 nm and its second harmonic) induced air-plasma is an effective way to generate high-power broadband terahertz pulse. The peak-power can reach more than MW and the spectral width can reach even more than 50THz. This terahertz radiation is a quasi-single-cycle broadband pulse. Effective control of the vector waveform of the THz pulse is of great importance for its wide application, which is a problem still unresolved so far. In this proposal, we intend to develop a technique of controlling the vector waveform of the THz pulse radiated from two-color laser excitation. Understand its physical mechanism and realize all-optical control of the parameters of the THz pulse (such as strength, spectrum, polarization, carrier-envelope phase, spatial distribution, etc.). Our work has great contributions to the development and application of broadband terahertz waves in the future.

太赫兹光谱在生物、医学、化学、农业及高速通信等领域均具有巨大的应用前景和需求。人们在对太赫兹光谱应用的探索过程中发现，发展高功率的宽带太赫兹源对这些应用的顺利推进是至关重要的。双色飞秒激光激发空气等离子体是产生高功率宽带太赫兹脉冲的有效方法，其峰值功率可以达到MW以上、频谱宽度可达到甚至超过50THz。这种太赫兹辐射源是一种近单周期的宽带脉冲，将这种辐射脉冲广泛应用的首要前提是实现脉冲矢量波形的精密操控，这是一个至今没有妥善解决的问题。本项目拟开展对双色飞秒激光激发的太赫兹脉冲矢量波形的研究，发展对太赫兹矢量波形有效调控的技术并了解其物理机制，进而实现对该宽带太赫兹脉冲各种参数（如强度、频谱、偏振、载波包络相位、空间分布等）的全光调控。本项目的研究工作对太赫兹辐射在多个领域应用具有迫切需求。

双色激光场与空气中的气体相互作用中产生的强太赫兹辐射源具有超宽的频谱宽度，是应用于太赫兹光谱测量最理想的光源，因而近几年受到了广泛的关注。之前的大量研究表明，此种太赫兹辐射源是一种近单周期的宽带脉冲，了解这种辐射脉冲的产生机制并实现对它各参数的精密操控是其广泛应用的必要前提。围绕本项目的研究计划和研究目标，主要开展了强激光与气体靶作用辐射超宽带太赫兹脉冲的实验和理论研究，研究这种宽带强太赫兹脉冲矢量波形等各参数灵活调控的物理机制，探索产生新型可控的强太赫兹辐射的新技术和新方法。经过项目组成员四年的努力，在强激光与气体靶作用辐射宽带太赫兹脉冲的新产生机制理论/实验研究以及等离子体产生太赫兹辐射的矢量波形、偏振态、频谱、强度等的调控方面都取得了显著进展：提出了基于飞秒强激光与气体靶作用产生超宽带强太赫兹辐射的两维太赫兹脉冲矢量波形理论模型，并利用该模型模拟双色激光场激发太赫兹脉冲在两个正交方向上的矢量波形，进而实现对该太赫兹脉冲偏振态（包括线偏振的偏振方向、椭圆偏振的椭率和旋性等信息）、频谱和强度等的灵活操控，首次实现在小型化的激光等离子体装置上产生各项参数可控的宽带强太赫兹辐射，不仅极大推进对双色激光产生太赫兹辐射机制的认识，也为开辟强太赫兹辐射应用奠定基础。