Threshold Conditions for Terahertz Laser Discharge in Atmospheric Gases

In this study, we accurately measured the breakdown thresholds in four atmospheric gases using the high-power terahertz radiation of the Novosibirsk free electron laser (NovoFEL). The breakdown intensities of the 130-μm radiation in a form of 74-ps pulses were equal to 1.1–1.4 GW/cm². These data have been compared with calculations based on a phenomenological criterion for a breakdown and the classical theory of stochastic microwave heating of electrons. Presented are threshold conditions for a quasi-continuous plasma discharge that is maintained by means of a sequence of pulses of the NovoFEL. At a pulse repetition rate of 5.6 MHz, the discharge quenching thresholds are 15–60% lower than the breakdown thresholds depending on the amount of plasma emerging.