Flexible spectrally tunable radiation sources for multi modal spectroscopic analysis

该项目的长期愿景是实现一种可调光源，用于同时在紫外线、近红外线和太赫兹范围内的多模态传感器应用。我们的目标是在应用期间开发一种基于单片可调谐二极管激光器的同时进行太赫兹和拉曼光谱的传感器。太赫兹和拉曼光谱解决不同的激发和相应的附加信息是有趣的几个应用。作为一个应用实例，我们的目标是通过太赫兹光谱检测相关废气和通过拉曼光谱检测烟尘颗粒。这种传感器的许多其他可能应用之一是控制包装食品：即使通过包装，食品的质量也可以通过拉曼光谱分析，并且THz光谱将能够分析包装内的气氛（例如水含量）。如果可以实现双色辐射源，其中两个波长的光谱距离可以从0到6.4nm电调谐，则可以通过差频产生覆盖光谱相关范围von 0到3 THz（例如对于在排气过程中相关的气体N2 O、NO、CO、NO2、SO2和H2O）。利用高达7 nm的相应光谱距离，还可以将宽的拉曼特征（例如无定形碳的拉曼特征）与干扰背景（如荧光或环境光）分离。因此，我们的项目目标是实现一个基于二极管激光器的单片集成辐射源，使可调谐双色操作高达7 nm的波长分离。在此基础上，我们的目标是实现一个多模态传感器，分析相关的尾气太赫兹光谱和烟尘颗粒的拉曼光谱。这种发展的基础是提高对激光器件横向设计（波导弯曲、臂耦合）的理解，以及对太赫兹产生和拉曼光谱给出的光源要求的理解。 我们选择830 nm作为多色二极管激光器的中心波长。一方面，这是拉曼光谱学的公认波长，其减少了潜在出现的荧光，并且所需的滤波器元件可用于该波长。通过光谱指纹检测拉曼光谱用于物质识别是可能的硅基检测器。另一方面，该波长也非常适合于基于LT-GaAs的光电导天线的THz产生，因为它很好地拟合LT-GaAs的吸收光谱。

The long-term vision of this project is to realise a tunable light source for simultaneous multi modal sensor applications in the UV, in the near Infrared, and in the THz-range. Our goal for the application period is to develop a sensor for simultaneous THz- and Raman spectroscopy on the basis of monolithically tunable diode lasers. THz- and Raman spectroscopy address different excitations and the corresponding additional information is interesting for several applications. As an application example, we aim to detect relevant exhaust gases via THz-spectroscopy and soot particles via Raman spectroscopy. One out of many other possible applications of such a sensor is to control packaged food: even through the packaging the quality of the food could be analysed by Raman spectroscopy, and THz spectroscopy would enable to analyse the atmosphere within the package (e.g. water content). If it was possible to realise a two-colour radiation source in which the spectral distance of the two wavelengths could be tuned electrically from 0 to 6.4 nm, one could cover the spectroscopically relevant range von 0 to 3 THz (e.g. for the gases N2O, NO, CO, NO2, SO2 and H2O which are relevant in exhaust processes) by difference frequency generation. With the corresponding spectral distances up to 7nm one could also separate broad Raman features (e.g. of amorphous carbon) from disturbing background like fluorescence or ambient light. Therefore, our project goal is to realise a diode-laser based monolithically integrated radiation source that enables a tunable two-colour operation with up to 7 nm wavelength separation. On the basis of this laser source, we aim to realize a multi-modal sensor which analyses relevant exhaust gases by THz spectroscopy and soot particles by Raman spectroscopy. A basis for this development is to improve the understanding of the laser devices with regard to their lateral design (curvature of waveguides, coupling of arms) and the understanding of the requirements for this light source given by the THz generation and Raman spectroscopy. We chose 830 nm as the center wavelength for the multi-colour diode laser. On the one hand, this is a well established wavelength for Raman spectroscopy which reduces potentially appearing fluorescence, and for which required filter elements are available. A detection of the Raman-spectra for substance identification through spectral fingerprints is possible with Silicon based detectors. On the other hand, this wavelength is also well suited for THz generation with LT-GaAs based photoconductive antennas since it fits well to the absorption spectrum of LT-GaAs.