GAUGE INDEPENDENT THEORY APPLIED TO A MODEL OF ATOMIC IONIZATION BY AN INTENSE LASER PULSE

V. D. RODRÍGUEZ; R. O. BARRACHINA

Foz do Iguaçu, Brazil

Workshop; 19th INTERNATIONAL LASER PHYSICS WORKSHOP; 2010

University of Sao Paulo, Brazil

In recent works the subject of the gauge dependence (or independence) of the theoretical descriptions of atom and molecule ionization by laser pulses has captured a great deal of attention. It is widely known that generally, not only the first Born approximation but also the so called Strong Field Approximations SFA are strongly gauge dependent. Therefore the question arises on which gauge should be used for a given problem. Until recently there was a kind of agreement on the superiority of the length form of the SFA [1]. However, the SFA in velocity gauge has been gaining consensus as the proper theory for quantitatively accounting for recent experimental results of Fluorine negative ions detachment [2]. Furthermore, even when a numerical treatment can be carried out in any of both gauges, it is well know that the velocity gauge is actually preferred due to the faster convergence of the angular momentum expansion of the electronic wave function. Among the efforts to clarify this controversy, explicitly gauge-independent theories have been proposed [3,4], as –for instance- the gauge-independent SFA, developed by Antunes Neto and Davidovich [4]. In order to test their theory at work, they apply it to a onedimensional system with an electron bounded by a delta-function potential. They presented a rather good agreement with full Time Dependent Schrödinger Equation (TDSE) simulations, but only calculated the first order term in the series expansion. No electron spectra, but only survival probabilities were reported. In particular, they use the unitary condition to deduce the total ionization probability. Based on this gauge independent SFA theory, in this communication we calculate both the first and second terms in the series expansion for the same atomic model. As expected, the series seems to be convergent. Furthermore, our results show that the ionization spectrum is by far more sensitive to the theoretical approximation. We also present calculations of the standard SFA and of an improved SFA that accounts for the population decay of the initial states owing to ionization. We show that this new theory is almost gauge invariant for the particular model considered. Other issues about gauge dependence in laser-atom ionization are also discussed. References 1. D Bauer, DB Miloševiæ, W Becker, Phys. Rev. A 72, 023415 (2005). 2. H. R. Reiss, Phys. Rev. A 76, 033404 (2007). 3. W Becker and D B Milosevic, Laser Physics 19, 1621–1625 (2009).D Bauer, DB Miloševiæ, W Becker, Phys. Rev. A 72, 023415 (2005). 2. H. R. Reiss, Phys. Rev. A 76, 033404 (2007). 3. W Becker and D B Milosevic, Laser Physics 19, 1621–1625 (2009).Phys. Rev. A 76, 033404 (2007). 3. W Becker and D B Milosevic, Laser Physics 19, 1621–1625 (2009)., Laser Physics 19, 1621–1625 (2009). 4. H. S. Antunes Neto and L. Davidovich, Phys. Rev. Lett. 53, 2238-2241 (1984).Phys. Rev. Lett. 53, 2238-2241 (1984).