Key trends in laser induced plasma structure revealed by longitudinally resolved optical diffractometry

We investigate the longitudinal evolution of laser-induced atmospheric plasma using transverse optical diffractometry and characterize the local plasma distribution using a supergaussian plasma density model. The supergaussian distribution, previously suggested by Bodrov et al., is used here to describe the plasma electron density, its transverse width, and critically for this work - to monitor the evolution of the transverse shape of the plasma throughout its longitudinal propagation. We identify distinct dynamical features recurring across a range of pulse intensities—termed the escape position , turning point , and refocusing behavior —and explore their underlying driving forces in the moderately tight-focusing regime in which the contributions of the Kerr nonlinearity are negligibly small. The supergaussian model provides a physically grounded framework that encompasses the conventionally used Gaussian and uniform density models and offers enhanced diagnostics and insights into the underlying physical mechanisms governing ultrafast air–plasma dynamics in the tight-focusing regime.