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We present a theoretical model of electromagnetic pulse emission and nozzle damage from high-power laser interactions with gas jets. As hot electrons are accelerated beyond the laser channel, they produce a positively-charged plasma that expands into the ambient gas until it reaches the gas jet nozzle. A strong plasma potential leads to electrical breakdown that ionises the gas even faster than the expanding plasma ions. When contact is made between the plasma and the conducting nozzle surface, a discharge current propagates to ground and an electromagnetic pulse is radiated via an antenna emission mechanism. Damage to gas jet nozzles is caused by heating from plasma ions rather than Ohmic heating via a discharge current. Our model agrees with experimental data from experiments on proton acceleration in near-critical plasmas at the Vulcan and VEGA-3 lasers., Comment: 32 pages (total), 8 figures, 1 table

This work shows for the first time experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser plasma interaction for laser driven secondary sources. Such currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons. Therefore, return currents can be used as a metrological online tool in the optimization of many laser-driven secondary sources and for diagnosing their stability. We demonstrate the destruction free measurement of return currents at the example of a tape target system irradiated by the 1 PW VEGA3 laser at CLPU at its maximum capabilities for laser-driven ion acceleration. Such endeavour paves the ground for feedback systems that operate at the high-repetition-rate of PW-class laser systems.