| 摘要 |
The invention relates to a process and device for photo-thermal spectroscopy (thermal wave analysis) of the single-beam process with double modulation type. The aim of developing a single-beam process which makes use of the advantages of the double modulation system in detecting the photo-thermally generated differential frequency without requiring partial beams and attains a high degree of intermodulation freedom, is achieved by the invention in that the intensity of the laser beam is modulated before impinging on the object in such a way that there are in the modulation spectrum essentially a carrier frequency (f1) and two side-band frequencies (f1-f2), where f2 is the basic pulse frequency of the modulation, a regulating detector and a regulating loop entering into the modulation process are used to suppress the component of the basic pulse frequency (f2) which is of the same phase as the mixed frequency consisting of the carrier and side-band frequencies, and, after interaction with the object, a measuring detector and a frequency and phase-selective device are used to measure the optical response of the object as an amplitude of the component of the basic pulse frequency (f2) which as a photo-thermal mixed product is of the same phase as the mixed frequency of the carrier frequency (f1) and the side-band frequencies (f1-f2). The invention is applicable to the interference-free and contactless analysis of the material parameters of regions of solid bodies close to the surface. |
