Ionization of Rydberg atoms in THz-laser fields at the transition from low to high scaled frequencies

We have studied the ionization of Rydberg–excited xenon atoms in THz-laser fields and by quantum dynamical calculations. The experimental threshold laser field strength for 10% ionization probability follows an n (ω/2π =1.04 THz) dependence (n effective principal quantum number) with additional weak resonance structures and shows that ionization does not occur by a Landau–Zener mechanism. At scaled frequencies of Ω = 0.71 to 5.6 the simulated threshold fields for ionization in oscillatory fields show a dependence on the principal quantum number n of n to n. PACS. 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) – 42.50.H Strong-field excitation of optical transitions in quantum system; multiphoton processes; dynamic