Study On Instrumentation Of Femtosecond Laser Pump And Probe Thermoreflectance System

Since the high spatial resolution,fast temporal resolution,and contactless measurement of femto-second laser pump-probe thermoreflectance technique,it has been widely used in research.In this work,the old two-color femto-second laser pump-probe thermoreflectance system is improved in many aspects for commercial instrumentation.It reaches high integration by designing and optimizing optical path system.Modulation followed with frequency doubling scheme replaces modulation following the frequency doubling scheme to enhance signal-to-noise ratio.Utilizing the Lab VIEW,the human-computer interaction interface is compiled.The control scheme is improved with modularization management.Many measurement functions are added with the outcome of improving efficiency remarkably.By introducing the high precision three-dimensional electronic-control sample stage,focusing the laser pot and choosing the measured point exactly become feasible.No objective lens device is established for the study on thermophysical properties of liquid and powder.In addition,the measurement system ranged from low temperature,high temperature,high pressure is established basing on the femto-second laser pump-probe thermoreflectance technique.Exploring the thermophysical property measurement of temperature from 4 K to 1500 K and pressure from ordinary pressure to high pressure,the practical scope of the old experimental system has been widen.Data analysis method of multi-layered structure sample is optimized and two simplified analysis models,simplified bi-layer model,simplified tri-layer model are proposed.By using matrix analysis,non-simplified model,simplified bi-layer model,simplified tri-layer model are compared.Both of the simplified model reduce the number of free parameter from multiple to one.But the simplified tri-layer model behaves better in the simulation and experimental research.The optimized data process method of multiple-layers structure sample is applied in the study on interface of Cu-Ti-Diamond nano-film and representative thermally conductive polymer composites.After the heat treatment,the TiC gradient intermediate layer is formed in the Cu-Ti-Diamond sample.Since the Cu/Diamond interface is bonded and TiC has the maximum phonon average velocity,it can weaken the acoustic mismatch between diamond and copper.And its thermal expansion coefficient,density,Debye temperature between copper and diamond,which significantly improved the Cu/Diamond interface thermal conductance.In the Al/PS/SAM/Sapphire structure samples,the thermal conductivity of aPS/SC-Al2O3 was improved remarkably by the NSL functionalization of SC-Al2O3,and it was found that changing the interface compatibility could improve the thermal conductance.The better the interface,the greater the thermal conductance of the interface.Vapor deposition of transducer layer is a critical process in sample pretreatment of femto-second laser pump-probe thermoreflectance technique.100nm aluminum transducer layers were deposited on different substrates with different deposition rates.The experimental results show that the thermal conductivity of the substrate vary from different deposition rates.By SEM,XRR measurements and the sensitivity analysis of it is discovered that the thermal conductivity and volumetric heat capacity of the aluminum transducer layer,the larger the deposition rate,the larger the grain of the aluminum transducer layer.When it increases to a certain extent,the irregularity of the surface grains increase.In the femto-second laser pump-probe thermoreflectance experiment,the thermal conductivity of the aluminum transducer layer is insensitive to the fitting,and the volumetric heat capacity is on the contrary.It can be concluded the deposition rate affect the femto-second laser pump-probe thermoreflectance experiment by having influence on the volumetric heat capacity of transducer layer.