Avalanche initiating electron produced by laser-induced tunneling

We have been able to eliminate all extrinsic sources of avalanche initiating electrons in ultrapure N2and He gas. Plasma formation is therefore inhibited until the laser intensity glows high enough to produce tunnel ionization of a molecule in the focal volume. This permits a record CO2laser intensity, as high as 10¹³W/cm²in a high-pressure gaseous target. For the first time the electron tunneling limit has been approached in a dense medium.