LAUSR

Characterizing the air plasma generated by the intense femtosecond laser pulses focused in air has gained attention in recent years to understand its role in many applications, such as terahertz generation and laser processing. Time-resolved complex-amplitude imaging is a powerful technique for characterizing such plasmas. Among various ways of obtaining the complex amplitude of the probe light, the Nomarski interferometer is one of the well-established configurations. However, despite its advantages in simplicity, conventional Nomarski interferometers are often limited in their spatial resolution to tens of micrometers, resulting in the obtained images being spatially averaged and losing accuracy. Here, we report on the development of a time-resolved Nomarski interferometer setup with sub-micrometer spatial resolution realized by incorporating a wide-separation-angle Wollaston prism used in the Nomarski interferometer. With this setup, we show that it is possible to image the time-resolved dynamics of laser-induced air plasmas, succeeding in observing even the internal structure of the plasma electron density distribution, such as spatial splitting, on the micrometer scale. Furthermore, our results were compared with numerical simulations and were found to demonstrate good qualitative agreement. Our results pave the path to the accurate characterization of air plasma, furthering our understanding of its basic physics and enabling more advanced applications.