Dynamic Measurement Of Energy Coupling Coefficient/Emissivity In Mid-infrared Band

The temperature dependence of laser energy coupling coefficient to the material is often the popular focus in the field of laser-matter interaction.Non-contact radiation temperature measurement method is suitable to measure the temperature of irradiated surface,however,it needs the dynamics of the emissivity in advance.The author designed and built a set of energy coupling coefficient/emissivity dynamic measurement device to measure several kinds of metals.The main research and achievement are as follow:(1)The design of energy coupling coefficient/emissivity dynamic measurement device is introduced in the thesis.The technical solution of the dynamic measurement was determined based on completely understanding of the principle of integrating sphere method for hemisphere reflectivity measurement,chopping and phase lock technique for suppressing background radiation and thermal imaging temperature measurement.(2)The energy coupling coefficient/emissivity dynamic measurement device was successfully set up.Accounting the limited imaging size of the thermal imaging system,the author designed the key components of the integrating sphere.The technology parameters of chopper,phase-locked amplifier,photoelectric detector and the filter are determined.The thermal imager was calibrated by using standard blackbody.The probe light reflectance of steel and aluminum alloy at room temperature were measured by using the device.The results are correspond with the results measured by China institute of metrology,which preliminarily shows that the results measured by this device are credible.(3)The energy coupling coefficient of 45# steel and aluminum alloy at 3.8μm changing with the temperature were measured under electric heating.The front surface of samples was roughly isothermal.The surface temperature were recorded by thermocouple and thermal imager at the same time.According to the gray curve recorded by thermal imager and the emissivity measured,the temperature of front surface is obtained by conversion.The results is consistent with temperature curve recorded by thermocouple,which indicates that it is feasible to determine the surface temperature through the emissivity of real-time measurement using this device.(4)The energy coupling coefficient of 45# steel at 3.8μm changing with the temperature were measured under laser heating.The temperature of radiation surface were measured by thermal imager.The changes of energy coupling coefficient of the sample with the temperature of radiation surface were obtained.The results are consistent with that of electric heating.The results show that,the energy coupling coefficient of aluminum alloy at 3.8μm basically remains unchanged in 25~480℃,the energy coupling coefficient of 45# steel increases sharply after 350℃ adopting electric heating while which increases sharply after 400℃ adopting laser heating.The oxidation reaction of 45# steel surface is the main cause of the increase of energy coupling coefficient.By real-time measuring emissivity,using thermal imaging to measure the temperature of laser irradiated surface,this kind of measurement method is the first try in domestic.The method set up by this article has important significance for research of changes of energy coupling coefficient with temperature.