Multiphoton Ionization Reduction of Atoms in Two-Color Femtosecond Laser Fields

Area of Science:

• Atomic Physics
• Quantum Mechanics
• Laser Spectroscopy

Background:

• Multiphoton ionization is a fundamental process in atomic physics.
• Controlling ionization is crucial for applications in attosecond science and materials modification.

Purpose of the Study:

• To investigate the effect of two-color femtosecond laser fields on atomic ionization.
• To understand the underlying mechanism of ionization reduction in multi-color laser fields.

Main Methods:

• Theoretical study using the time-dependent Schrödinger equation.
• Experimental investigation of atomic ionization using femtosecond laser pulses.

Main Results:

• A significant reduction in ionization probability was observed when a weak 800 nm laser pulse was applied concurrently with a 400 nm pulse.
• Ionization reduction occurred irrespective of the relative phase between the two laser pulses.
• Simulations showed that 800 nm photons assist in launching electrons into high angular momentum Rydberg states, which are less likely to ionize.

Conclusions:

• Two-color laser fields offer a novel method to control and reduce atomic ionization.
• The mechanism involves stabilizing electrons in high-lying Rydberg states, preventing their escape.
• This phenomenon is demonstrated for hydrogen and helium and is expected to be applicable to other atoms with appropriate laser tuning.