Submillimeter-laser-induced air breakdown

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.