Electron Nonequilibrium Heat Transport Time In Copper And Alloy Films Excited By Dual Femtosecond Pumped Beams

With the wide application of nano-metal films in the field of micro-mechanics and micro-electronics,the thermal barrier effect and scale effect in the film have become important factors limiting the further development of the technology.Therefore,research on the thermal effect of nano-film materials has become a research hotspot.The pump detection technology of femtosecond laser provides an important means for observing and studying the micro energy conversion and transfer process.In this paper,the pumping detection technology of femtosecond laser is used to observe the transient reflectance change of the surface of nano-metal film,and the non-equilibrium heat transport phenomenon is analyzed to study the relaxation time.The content of this article mainly includes the following parts:The first part briefly introduces the non-equilibrium heat transport process in the metal film,the two-temperature model describing the electron temperature and the lattice temperature,and the relationship between the electron-lattice temperature and the transient reflectance of the film surface.The second part of the work is divided into two aspects,on the one hand is the establishment of a two-beam femtosecond laser pump-detection experimental system,the dual beam refers to the use of a beam splitter to split a pump laser into two equal energy Pump light.This section introduces the main experimental instruments and their working principles and the construction of experimental optical paths.On the other hand,the preparation of experimental samples was introduced,including the selection of metal targets,film substrates,magnetron sputtering coating principles,equipment and coating steps.The third part is to measure the surface transient reflectivity of Cu,Cu-Ag,Al and Ti-Al nano-films with different pumping power and thicknesses,to study the non-equilibrium heat transport process in the films,to analyze the movement of electrons and lattices,and to discuss the heating time of electrons,the heating timeand relaxation time of lattices.The regularity and influencing factors among them.The study found that:For Cu and Cu-Ag films,only when the thickness of the films is large and the pump power is high,two nonequilibrium heat transports occur in the films,and the relaxation time of the two nonequilibrium heat transports is not exactly the same,which is caused by the uneven distribution of pump light in the experimental optical path.The amplitude of reflectivity oscillation of metal film surface is proportional to the total laser pumping power.For Al and Ti-Al films,the equilibrium heat transport can be excited with a smaller thickness or a smaller pump power.When the film thickness is small,the relaxation time of Al and Ti-Al films is also small,and the influence of pump power on the relaxation time is not obvious.When the pump power is high,the relaxation time in Al and Ti-Al films is also large,and the effect of film thickness on the relaxation time is not obvious.