Thermal Wave Imaging Detection System And Its Application Based On Photo-thermal Effect

Thermal wave imaging detection technique based on photothermal effect applied to non-destructive detection of solid material is the research with lots of potential at this current stage. The technique has advantages of high sensitive, non-contact and non-destructive in theory, it also has the ability of depth profiling that can be used in detecting the defects at different depth under subsurface of solid material. So it is employed as delaminating imaging analysis method on metal material, semi-conductors, integrates circuit, film material, etc. and is thought highly of by various application field.In this paper, the theory of thermal wave detection technique is described and the investigative actuality and developmental trend of the technique is summarized after the reading of many China and foreign countries' references, then new research objectives are brought forward. Therefore, a volume absorption model of thermal conduction is established, using the property of thermal wave diffusion, the surface temperature of sample that relates to depth of the defects and frequency of pumping laser is determined by solving the thermal conduction equations. Miniaturization imaging detection system based on pthotothermal deflection technique is aboratively designed. The system has advantages of compact structure, easy to operate and miniaturization, etc. because the pumping light and detecting light are especially designed and the modules of light, mechanism, electricity, and computer are reasonably configured and designed. The experimental set in which semi-conductor lasers are used as pumping laser and detecting laser is established. The theory educed by the model is verified based on large numbers of experiments, the information of different depth buried under the surface of sample is obtained and the delaminating detection of subsurface defects is made under the differential operating on two different depth information of metal Al by means of vertical photothermal deflection detection method. The spatial resolution of thermal wave amplitude signal and phase signal are studied through experiments, then the conclusion that thermal wave imaging detecting technique can only be applied to lamina material is established. Some thermal wave images of optical films are obtained by detecting the thermal wave signal of compound films and metal films that have been damaged by laser, the degree and the spatial position of laser induced damage of optical film can be deflected by obtaining thermal wave image directly, and laser damage threshold of optical film can be calculated by dealing with the thermal wave amplitude signal detected on the damage position of optical film. While thermal wave image detection technique is applied to optical film, a method, named as synthetical evaluation method, based on various properties of optics and calorific of optical films which can evaluate the integral quality ofthe optical films is developed. Because thermal wave image detection technique has properties of high sensitive, nondestructive to sample and direct observation to the detected result, wider applying prospect of this technique is also shown in nondestructive evaluating the integral quality of optical films.The six experimental results indicate that: (1) information of subsurface structures at different depth of material can be obtained by applying different modulation frequencies of pump laser, the lower the frequency of pump laser is, the deeper the subsurface structure of material is reflected; (2) deeper subsurface structure can be shown by using thermal wave phase signal than by using amplitude signal under the same modulating frequency, but the spatial resolution of detection by phase signal is inferior to that by amplitude signal, phase signal can't reflect subsurface structure whose transversal size is smaller than depth where the structure is located; (3) the detection depth is finite while using diffused thermal wave to detect subsurface defects. When modulate frequency is too low, the signals will be in saturation and the values...