Study On Modulated Crossed-Beam Near-Field Detection Thermal Lens

Thermal lens spectroscopy (TLS), as a photo-thermal technology with high sensitivity and low detection limits, has been widely applied to the trace analyses and measurements of the weak absorption, the photochemistry reaction and the fluorescent quantum effects. In recent years, the near-field detection TLS, which enables a more compact and stable thermal lens spectrograph, draws researcher's attention extremely. This thesis mainly focuses on the development of a novel near-field detection TLS and its applications. The main points of this thesis are the following:1. The theory of Fresnel diffraction is used to build the theoretical model of the modulated crossed-beam near-field detection thermal lens (MC NFD-TL). The thermal lens signal acquired from the lock-in amplifier is calculated and analyzed theoretically.2. A MC NFD-TL instrument is built. The distribution of thermal lens signals on the detection plane is investigated experimentally and theoretically. Numerical simulation and experiments are processed to investigate the influences of the detection distance and the modulated frequence on signals. Moreover, the MC NFD-TL system is optimized theoretically.