"Front heating-rear detection type Thermoreflectance method" is numerically reproduced by developed hybrid molecular dynamics method which couples classical molecular dynamics method with two temperature model. Simulation is conducted in order to inverstigate transient thermal behavior in femtosecond thermoreflectance method that employs short pulse and high intensity laser compared to traditional thermoreflectance method. In the simulation, aluminum thin film whose thickness is 75nm is irradiated with picosecond and femtosecond pulsed lasers with the same fluence. As a result, increment of laser intensity due to shorted pulse width enhances intrinsic vibration all in the film and makes temperature disturbance on detection surface large. Consequently, the shortening of laser pulse with makes uncertainty of measurement large.
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