Submillimeter-laser-induced air breakdown

Abstract

We report the first demonstration of laser‐induced air breakdown at submillimeter wavelengths. An optically pumped D₂O oscillator‐amplifier laser system which produced 75‐ns pulses at the megawatt level on the 385‐ and 359‐μm transitions was used. Focusing the 10‐cm‐diam laser beam with a 20‐ or 38‐cm‐focal‐length mirror onto an arbitrary surface to produce initial ionization caused multiple air breakdown plasmas with a threshold on the order of 1 MW cm⁻². Theoretical (ω²+ν²)/ν scaling from the ruby and the neodymium laser air breakdown thresholds, where ω is the laser angular frequency and ν is the electron‐molecule collision frequency, is in agreement with this initial experimental result.