# Cause and description of 'secondary' probability peaks in Above Threshold Ionization

While reading about above-threshold ionization, I found this graph on the wikipedia page about ATI:

The $x$ axis represents the kinetic energy of the electron and the $y$ axis shows the differential probability.

I could understand why the average probability drops for higher electron kinetic energies. I also understand the cause of the peaks, 3 of which are visible in the picture. However, in the region between the peaks, there are several local maximums. Why are these maximums visible?

They do not seem to follow a constant count: there are 5 of them between the first ATI peak and the second; there are 4 of them between the second ATI peak and the third. After the third, they seem to become indistinct.

## 1 Answer

They're an experimental artifact:

The theoretical angle integrated photoelectron spectrum (PES) of Hydrogen from a fully ab-initio TDSE calculation. The three larger peaks are the Above threshold ionization peaks. The smaller oscillations are caused by interference between cycles. Laser parameters: 10 cycle Sine pulse, 95eV photons, 1x10^15 Wcm^-2.

• @Chair Unfortunately, the original article seems to be behind a paywall. Perhaps you can find a copy of it somewhere on the web: "Above-threshold ionization spectrum of hydrogen using B-spline functions". Journal of Physics B: Atomic, Molecular and Optical Physics. 30 (1): 77–91. – Bob Jacobsen Jul 30 '18 at 15:37