Abstract
A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations.
Highlights
IntroductionGas breakdowns generated by high-power optical pulses can be traced back to the groundbreaking era for lasers [1,2]
Academic Editors: BernhardGas breakdowns generated by high-power optical pulses can be traced back to the groundbreaking era for lasers [1,2]
Since laser-induced breakdowns (LIBs) belongs to a threshold-like process with respect to the peak intensity of the laser pulse [16,17,18], determining the breakdown threshold has long been a critical issue for reliable results of the developed applications
Summary
Gas breakdowns generated by high-power optical pulses can be traced back to the groundbreaking era for lasers [1,2]. The LIB is generally described as the formation of ionized gas or plasma during or by the end of the excitation of the laser pulse. The breakdown and ionization of the gas molecules are triggered when the electric field of the laser pulse is greater than that of the binding electrons to their nuclei [11]. Since LIB belongs to a threshold-like process with respect to the peak intensity of the laser pulse [16,17,18], determining the breakdown threshold has long been a critical issue for reliable results of the developed applications
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