Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO<sub>2</sub> laser
نویسندگان
چکیده
Understanding the formation and long-timescale evolution of atmospheric plasmas produced by ultrashort, long wavelength IR (LWIR) pulses is an important but partially understood problem. Of particular interest are in air with a peak laser intensity $\sim$10$^{12}$ W/cm$^2$, so-called clamping observed LWIR guiding experiments where tunneling multi-photon ionization operative at near-IR or shorter wavelengths inoperative. We find that avalanche breakdown on surface aerosol (dust) particles can act to seed above 200 GW/cm$^2$ threshold when train 3 ps 10.6 $\mu$m separated 18 used. The first appears best focus propagates backwards towards focusing optic as plasma density approaches critical makes forward propagation impossible. velocity backward propagating be high 10$^9$ cm/s, order magnitude greater than measured ns pulse-produced explained rather well wave mechanism. Transverse expansion similar assisted UV photoionization secondary longitudinal mechanism roughly 10 percent shots. When cm size, TW power beam propagated, interception guaranteed several (40 cm$^{-3}$) sites appear, each initially producing near plasma. On ns-1 $\mu$s timescale, shockwaves from site expand radially coalesce produce large hot gas channel. radial agrees prediction blast theory developed for ultrafast detonations.
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ژورنال
عنوان ژورنال: Physics of Plasmas
سال: 2022
ISSN: ['1070-664X', '1527-2419', '1089-7674']
DOI: https://doi.org/10.1063/5.0086771