The Long Nonequilibrium Heat Transfer Time of Electrons in Pt Thin Films Under the Heating of Double-pump Femtosecond Laser Beams
X.F. Xu, J. B. LI, X.H. Yang, S. Pan and Y.F. Gao
Under the excitation of femtosecond laser pulses, the time-resolved observation of the nonequilibrium heat transfer process of the hot electrons in Pt films is studied using the femtosecond transient thermal reflection technique. The nonequilibrium heat transfer phenomenon plays a positive role in solving the problem that the devices are damaged in the processing of the laser heating the metals. The thickness of the Pt metal films on K9 glass and a monocrystalline Si silicon substrate is 20 and 40 nm, respectively, and the Pt films are deposited by the magnetron sputtering technique. The nonequilibrium heat transfer time of the electrons in the Pt films is measured by detecting the transient reflectivity of the probe beam on the Pt films. The results show that by the heating of the two femtosecond pump beams, the nonequilibrium heat transfer time of electrons in the 20 nm thick Pt film on a K9 glass substrate is as long as 130 ps, much more than tens of picoseconds.
Keywords: Ti-sapphire laser, femtosecond laser, K9 glass, Pt film, nonequilibrium heat transfer, transient thermal reflection, femtosecond transient thermoreflectance (FTTR) method