Theoretical and experimental study of femtosecond pulse laser heating on thin metal film

Ultrashort pulse laser heating is not only capable of resolving and observing the ultrafast interaction of energy carriers, i. e. electrons, phonons, but also widely applied to material processing, i. e., laser ablation. However, the previous theories, i. e., two-temperature model, parabolic one-step model, can be applied only to some limited segments. In this paper, according to the two-temperature model and Fourier' s law, a general theoretical model is presented for the description of the entire heat relaxation process after the thin metal film deposited on the substrate has been heated by the ultrashort pulse laser. Moreover, the heat conduction process is also experimentally studied by using the rear-pump front-probe transient thermoreflectance technique on Au/glass and Au/SiC at 300 K, and the theoretical prediction accords well with the experimental result, which illustrates the validity of the present theoretical model. Based on the good agreement between theoretical predictions and experimental data, the electron-phonon coupling factor of the thin gold film and thermal boundary conductance of the Au/glass and Au/SiC interfaces are extracted and the measured results are in good agrement with the previous reported values. The electron-phonon coupling factor is close to that of the bulk material and does not exhibit size effect. The thermal boundary conductance is greater than the prediction of diffuse mismatch model, and the reasons responsible for the discrepancies are electrons participating in the interfacial heat conduction, interfacial atom diffusion and inelastic scattering.