case where only NS double ionization is included. It is clear that when the ionization
becomes deeper, the multi-electron effect becomes important. This suggests that one
electron TDSE in (2.1.6) is not enough, and multi-electron TDSE should be solved
for realistic calculation.
2.2 Laser as Electromagnetic Waves
Lasers are a bunch of mono-energetic photons in quantum physics and
electromagnetic field in classical physics. Depending on a problem, it is better to
choose one of two views convenient for analysis and understanding. Most of the
analysis of the coupling of lasers and matters in the present text is carried out by
assuming electrons are classical point charge, and the laser electric and magnetic
fields are given by Maxwell equations.
Under the force by oscillating electromagnetic field, electrons make
predominantly the local electric current compared to the ions, because the electron
mass is more than 1000 times smaller than the ion mass, although they have almost
the same charge. It is in general enough to consider the coupling between the laser
fields and electron motion. Therefore, we are asked to solve the coupled system of
Maxwell equations and the electron motions. It is, however, not so easy to solve the
10
3
10
2
10
1
10
14
Intensity (W/cm
2 )
Ion signal (arb.units)
10
15
10 0
10
-1
10
-2
10
-3
Fig. 2.6 Same as Fig. 2.5
for three ionization stages of
argon as a function of peak
laser intensity. The previous
data has been well refined to
clearly identify multielectron effect near the
threshold of ionization start.
Three different theoretical
curves are plotted as
explained in the text
2.2 Laser as Electromagnetic Waves
39