Laser Induced Temperature Modulation Spectrum Testing

Laser cooling of solids is based on the anti-Stokes fluorescence cooling theory.In 1995,it was proved experimentally that solid materials can be cooled by laser for the first time.Although the temperature drop is only 0.3K,after years of development,the field of solid materials laser cooling has achieved fruitful research results.Exploring new cooling materials is one of the research topics in laser cooling of solid materials.External quantum?_extand background absorption coefficientare key parameters to quantify the laser cooling performance of materials,which are related to the characteristics of materials themselves.In this paper,the two parameters and were measured and analyzed.The experiment to measure these two parameters is called laser-induced temperature modulation spectrum test,or LITMo S test for short.First,since contact temperature measurement in laser cooling experiments introduces an additional thermal load,resulting in unsatisfactory sample cooling.Therefore,we introduce two non-contact temperature measurement methods commonly used in laser cooling experiments on solid materials:differential fluorescence spectroscopy(DLT)and thermal cameras,which uses the relationship between spectral linewidth and temperature and is a highly sensitive non-contact temperature measurement technique.As a non-contact temperature measurement device,thermal cameras do not introduce additional thermal load to change the target temperature during the temperature measurement process,so it is ideal for the measurement of sample temperature in laser cooling of solid materials.Secondly,the non-contact temperature measurement method of thermal cameras is used in the room temperature LITMo S test.However,the temperature measurement resolution of commercial thermal cameras could not meet the requirements of experimental temperature measurement resolution.Therefore,we calibrated the thermal cameras before the experiment and improved its temperature resolution to±0.1?.The temperature measurement error is small,which can satisfy the precise measurement of relevant parameters in laser cooling experiment of solid materials.Finally,we conducted experiments with a calibrated thermal imaging camera to study Yb³⁺:Lu Li F₄crystals of the same size and different concentrations as well as the same concentration and different sizes,respectively,to derive their corresponding external quantum efficiencies and background absorption coefficients,and found that the theoretical and experimental data are in good agreement,thus laying the foundation for precise measurements in laser cooling experiments on solid materials.