Time-resolved optical probing of nanosecond laser-induced breakdown plasma in polymethyl methacrylate (PMMA)

In this paper, laser-induced optical breakdown in a transparent dielectric was studied by pump–probe beam method. The breakdown was induced by Nd:YAG nanosecond laser beam in polymethyl methacrylate (PMMA). The main laser beam was separated by a splitter and used as probe beam. An appropriate optics used to direct the probe beam passing through the breakdown region perpendicularly to the pump laser beam. Using fast photodiodes and oscilloscope, the transmitted/ reflected signals (associated with the probe/ pump beam) were monitored. Analyzing these signals can be used to describe the breakdown process. The results show that the dynamics of transmissivity and reflectivity of the produced plasma depend on the pump laser intensity.