Resonance-enhanced multiphoton-ionization photoelectron spectroscopy by a rectangular amplitude modulation

In this Brief Report, we present a scheme to control the (2+1) resonance-enhanced multiphoton-ionization (REMPI) photoelectron spectrum in cesium (Cs) atom by shaping the femtosecond laser pulse with a rectangular amplitude modulation. We show that the amplitude-shaped laser pulse can induce a hole in the (2+1) REMPI photoelectron spectrum, and the position and width of the hole depend on the amplitude step position and amplitude modulation width. We also show that a high-resolution REMPI photoelectron spectrum and the fine energy-level structure of the excited states can be obtained by observing the holes in the (2+1) REMPI photoelectron spectrum. We believe that these theoretical results can provide a feasible method to study the excited-state or Rydberg-state structure and the laser-induced photoionization dynamics.