基于飞秒激光的太赫兹时域频域特性调控方法研究

THz radiation generated by plasma introduced by femtosecond laser pulse is expected to provide important way for remote THz imaging and spectral detection; More powerful THz pulse generation and its control are the key technologies to expand the application of THz radiation. This project based on the generation of THz radiation from femtosecond laser pulse explores new methods to improve the THz intensity, and control THz time domain and frequency domain characteristics on ultrafast and remote way. Control the intensity, polarization state, phase information of the terahertz radiation through controlling the dielectric refractive index, ionization cross section, nonlinear coefficient induced by molecular alignment. These processes could be realized on femtosecond scale as the molecular alignment revivals are picosecond scale. Make dual-color pulse passing through the periodic structure produced by the plasma grating through the interaction of multi-filaments, the terahertz intensity could be increased dramaticlly with the Quasi-phase matching. Adjust the laser spot to form a reservation of the filament, and thus the filament length could be increased more than tenfold with the nonlinear effect from the filaments to produce more powerful terahertz intensity. Based on these processes, new prototype devices could be invented to control time-frequency domain characteristics fast on THz wavelength range. This research project has important scientific significance for providing precise methods for THz transmission over a long distance, remote imaging, spectral measurement and the strong THz radiation source.

利用飞秒激光诱导等离子体产生THz辐射可望为实现远距离THz成像和光谱探测提供重要方法；高峰值功率THz脉冲产生与远程调控是拓展THz应用的关键。本项目立足于飞秒激光诱导等离子体产生THz辐射，探索新方法提高THz产生强度，并对THz时域频域特性进行超快远程控制。利用飞秒激光激发气体分子的空间排列，基于分子排列的周期性超快回复，实现介质折射率、电离截面、非线性系数等控制，实现对THz强度、偏振、相位的远程控制，控制时间达到飞秒量级；通过两束光丝相互作用形成等离子体光栅，将产生THz辐射的双色脉冲与等离子体光栅的周期性结构相互作用，通过准相位匹配大幅度提高THz强度；通过光斑整形制备光丝的储备能库，利用非线性相互作用增长光丝，以实现更强的THz辐射；基于这一系列过程，发展THz时-频域快速精密控制的新型原型器件。本项目研究将为THz远距离传输、成像、光谱测量提供精密控制方法和强THz辐射源。

本项目围绕飞秒激光诱导等离子体产生THz辐射以及探索高功率THz产生方法展开一系列研究，主要包括：利用激光等离子体光栅实现THz频率调制；利用分子排列实现飞秒光丝中非线性过程调制；研究了半导体镀覆纳米介孔薄膜材料的表面THz及光电子发射机制。该研究过程实现了对THz强度、偏振、相位的远程控制，控制时间达到了飞秒量级；将产生THz辐射的双色脉冲与等离子体光栅的周期性结构相互作用，通过准相位匹配大幅度提高THz强度，同时利用等离子体光栅的周期性结构实现THz频率调制；通过研究纳米金属薄膜材料在超快激光作用下的电子运动过程，实现THz辐射增强。为THz光谱分析、光谱成像提供重要意义；除此之外，纳米介孔材料表面等离激元诱导的局域场增强和强耦合作用，可突破衍射极限,将电磁波约束在亚波长尺寸范围内传输，为实现THz波超分辨成像提供新方法。