Electron- and ion-beam transportation channel formation by laser ionization based on resonance saturation—LIBORS

Abstract

We have been able to show that ’’laser ionization based on resonance saturation’’, LIBORS, represents a powerful new form of laser interaction that can be used to efficiently couple laser energy into either a cold gas or a plasma. In essence, the dense population of resonance-state atoms resulting from laser resonance saturation represents both a reservoir of energy that rapidly provides translation energy to the free electrons through superelastic collisions and a large pool of atoms having an ionization energy reduced by the laser photon energy. We show that over a wide range of conditions LIBORS can be superior to both multiphoton ionization and inverse bremsstrahlung by many orders of magnitude. Indeed, LIBORS appears to be particularly well suited to create long plasma channels needed for electron- or ion-beam transportation in future inertial fusion schemes. We have estimated that a suitably tuned laser pulse of about 0.7 J and 400-nsec duration should be capable of creating a plasma channel with an electron density of close to 1015 cm−3 over an area of 0.2 cm2 for a length of 5 m in sodium vapor of about 0.1 Torr. A similar result should be possible in lithium vapor.