Avalanche initiating electron produced by laser-induced tunneling

We have been able to eliminate all extrinsic sources of avalanche initiating electrons in ultrapure N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and 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 CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser intensity, as high as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a high-pressure gaseous target. For the first time the electron tunneling limit has been approached in a dense medium.