Heat transfer in metal films irradiated by combined nanosecond laser pulse and femtosecond pulse train

Heat transfer in a copper film irradiated by a femtosecond (fs) laser pulse train and by an integrated dual laser beam of a nanosecond pulse with a fspulse train was studied using the semi-classical two-temperature model. The critical point model with three Lorentzian terms was employed to characterize transient optical properties for the laser energy deposition. The effects of pulse number and separation time on the thermal response were investigated. The results showed that with the same total energy in a fs-pulse train, more pulses for shorter separation time, e.g., 1 ps, and fewer pulses for longer separation time, e.g., 100 ps, can achieve higher lattice temperature. For a dual laser beam, the lattice temperature can be increased by setting the pulse separation time as short as possible, e.g., 1 ps.