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首页> 外文会议>Conference on Laser Applications to Chemical and Environmental Analysis, Feb 11-13, 2000, Santa Fe, New Mexico >Time-Resolved Optical Heterodyne Detected Raman Induced Kerr Effect Spectroscopy for Chemical Analysis
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Time-Resolved Optical Heterodyne Detected Raman Induced Kerr Effect Spectroscopy for Chemical Analysis

机译：时间分辨光学外差检测拉曼诱导的Kerr效应光谱法进行化学分析

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摘要

Coherent light scattering techniques such as CARS (coherent anti-Stokes Raman scattering) are especially useful in probing adverse environments such as flames and plasmas. Phase matching requirements lead to a coherent signal output that is highly directional, permitting spatial filtering of the signal from background radiation. Use of single frequency lasers requires a second laser to scan the Raman-active vibrational frequency spectrum of the material of interest, and can lead to a complex and spatially non-compact instrumentation for field work. On the other hand, a complete Raman spectrum can be potentially obtained in a single laser shot by use of a broad band laser source. In this paper, we describe a time-domain approach that relies upon a broad band, femtosecond laser source that is sensitive to weak depolarized intermolecular and intramolecular Raman modes that can be used as signatures to distinguish chemical species. This so-called femtosecond optical heterodyne detected Raman induced Kerr effect spectroscopy (OHD-RIKES) in one form or another has been employed by many ultrafast laser laboratories in their studies on ultrafast dynamics in condensed phases. Although femtosecond OHD-RIKES and traditional frequency-domain depolarized light scattering experiments extract the same information, OHD-RIKES more reliably reveal the very low frequency information of the intermolecular Raman spectrum. This low frequency region is sensitive to inhomogeneities of the intermolecular environment, temperature, and molecular symmetery. We demonstrate this technique by employing aniline (benzene with one of its hydrogen atoms substituted with a NH2 amino group) as the chemical species. For the sake of completeness we briefly describe the experimental apparatus, although it has been accounted for in detail elsewhere, and the Fourier transform procedure for extracting the intermolecular and intramolecular frequency spectrum. Figure 1 is a schematic of the experimental apparatus.
机译：相干光散射技术（例如CARS（相干反斯托克斯拉曼散射））在探测不利环境（例如火焰和等离子）中特别有用。相位匹配要求导致相干信号输出具有高度方向性，从而可以对来自背景辐射的信号进行空间滤波。单频激光器的使用需要第二个激光器来扫描目标材料的拉曼活性振动频谱，并且可能导致用于现场工作的复杂且空间紧凑的仪器。另一方面，可以通过使用宽带激光源在单个激光束中潜在地获得完整的拉曼光谱。在本文中，我们描述了一种时域方法，该方法依赖于宽带飞秒激光源，该激光源对弱去极化的分子间和分子内拉曼模式敏感，可以用作区分化学物种的标记。这种所谓的飞秒光学外差检测拉曼诱导的克尔效应光谱（OHD-RIKES），一种或另一种形式已被许多超快激光实验室用于研究凝聚相中的超快动力学。尽管飞秒OHD-RIKES和传统的频域去偏振光散射实验提取了相同的信息，但是OHD-RIKES更可靠地揭示了分子间拉曼光谱的极低频信息。该低频区域对分子间环境，温度和分子对称性的不均匀性敏感。我们通过采用苯胺（苯的氢原子被NH2氨基取代的苯）作为化学物质来证明该技术。为了完整起见，我们简要描述了该实验设备，尽管在其他地方已对其进行了详细说明，并介绍了提取分子间和分子内频谱的傅里叶变换过程。图1是实验装置的示意图。

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