Setup for nonlinear multi-terahertz spectroscopy

本提案的目标是建立一个实验装置来进行凝聚态物质的非线性多太赫兹光谱。中心特征是强烈的飞秒激光脉冲，中心频率可调，从远红外到可见光光谱范围。重点是多太赫兹（THz）范围内的电磁脉冲，中心频率为1至50太赫兹，场强为10 MV/cm和3 T及以上。通过将这种脉冲应用于固体，我们将有选择地触发和询问电子的动力学，它们的自旋和晶格。这种泵浦探测方法的目标是揭示和理解不同自由度之间的耦合机制。一个重要的例子是磁序与晶格（即声子）之间的相互作用。使用相同的方法，我们还将研究溶剂，以获得对分子及其耦合的集体运动的新见解。这些实验的潜在应用是固体中磁性信息的选择性写入和传输以及新溶剂状态的制备，这可能使更有效的化学反应成为可能。为了建立这样的设置，(i)可见光、红外和太赫兹频率范围内的强激光脉冲源，（ii）表征脉冲并将其引导到实验中的组件，以及（iii）用于低噪声检测和基于计算机的信号采集的组件是必要的。点(i)需要一个放大的钛：蓝宝石激光系统（脉冲能量~7 mJ，脉冲持续时间35 fs，脉冲重复率1 kHz，中心波长800 nm），随后有两个红外光学参量放大器（波长范围分别为1.16-1.6µm，信号和惰轮分别为1.6-2.6µm）。转换效率为25%（信号+惰轮）和两个混频器（和频和差频）以及合适的非线性光学晶体和光学和光机械部件（如镜子，透镜，偏振光学和光/旋转平台）。对于（ii），需要功率计，光谱仪，自相关器和相机，而（iii）需要光电探测器，示波器，电子放大器和基于计算机的数据采集硬件等组件。拟议的设置对于执行正在运行、提交和计划的第三方资助项目至关重要。由于申请人的研究小组在多太赫兹泵浦探针实验方面具有丰富的经验，因此预计该装置的建立将具有时间效率。

The goal of this proposal is to build an experimental setup to conduct nonlinear multi-terahertz spectroscopy of condensed matter. Central feature are intense femtosecond laser pulses with tunable center frequency from the far-infrared to the visible spectral range. The focus is on electromagnetic pulses in the multi-terahertz (THz) range with center frequencies from 1 to 50 THz and field strengths of 10 MV/cm and 3 T and beyond. By applying such pulses to solids, we will selectively trigger and interrogate the dynamics of electrons, their spins and the crystal lattice. The goal of this pump-probe approach is to reveal and understand the coupling mechanisms between the various degrees of freedom. An important example is the interaction between magnetic order and the crystal lattice (i.e. phonons). Using the same approach, we will also investigate solvents to gain new insights into the collective motions of the molecules and their couplings. Potential applications of these experiments are the selective writing and transport of magnetic information in solids and the preparation of new solvent states, which may enable more efficient chemical reactions. To build such a setup, (i) sources of intense laser pulses in the visible, infrared and THz frequency range, (ii) components to characterize the pulses and steer them to the experiment as well as (iii) components for the low-noise detection and computer-based acquisition of the signals are necessary. Point (i) requires an amplified titanium:sapphire laser system (pulse energy ~7 mJ, pulse duration 35 fs, pulse repetition rate 1 kHz, center wavelength 800 nm) with two subsequent infrared-optical parametric amplifiers (wavelength range 1.16-1.6 µm and 1.6-2.6 µm for signal and idler, respectively, and conversion efficiency 25% for signal+idler) and two frequency mixers (sum and difference frequency) as well as suitable nonlinear-optical crystals and optical and opto-mechanic components (such as mirrors, lenses, polarization optics and translation/rotation stages). For (ii), power meters, spectrometers, an autocorrelator and cameras are needed, while (iii) requires components such as photodetectors, oscilloscopes, electrical amplifiers and hardware for computer-based data acquisition. The proposed setup is essential for the implementation of running, submitted and planned third-party-funded projects. Because the applicant’s research group has significant experience with multi-THz pump-probe experiments, a time-efficient building of the setup is expected.