Time-resolved detection of structural change in polyethylene films using mid-infrared laser pulses

Abstract

Some of the vibrational modes of crystalline organic polymers are known to be sensitive to the structural change from the crystalline phase to the amorphous phase, and vice versa. Using a mid-infrared (mid-IR) pulse from a free-electron laser as a probe, we demonstrate the time-resolved detection of structural change in crystalline polymer (polyethylene) films upon laser heating by a Q-switched Nd:YAG laser. Transmittance of the resonant mid-IR pulse almost instantaneously changes before and after the Nd:YAG laser pulse if its fluence is sufficient to induce the structural change in the film. The developed technique would be useful to study the time-dependent dynamics of the structural change in various materials.