Strong-field two-photon absorption in atomic cesium: an analytical control approach

Area of Science:

• Atomic physics
• Quantum optics
• Strong-field laser physics

Background:

• Two-photon absorption is a nonlinear optical process where an atom absorbs two photons simultaneously.
• Strong-field laser-atom interactions exhibit complex phenomena due to intense electromagnetic fields.
• Laser pulse shaping allows precise control over the temporal and spectral properties of light.

Purpose of the Study:

• To analytically control and experimentally investigate two-photon absorption in cesium atoms under strong-field conditions.
• To understand the influence of laser pulse chirp on atomic excitation.
• To explain the underlying physical mechanisms enhancing the two-photon absorption process.

Main Methods:

• Experimental setup using gaseous cesium atoms, a femtosecond laser amplifier, and a programmable pulse-shaper.
• Application of shaped laser pulses with positive and negative chirp, and Gaussian pulses.
• Analytical calculations employing strong-field phase matching.

Main Results:

• Both positively- and negatively-chirped laser pulses enhance two-photon excitation from the 6s to the 8s state in cesium atoms compared to Gaussian pulses.
• The enhancement is attributed to the temporal shape of the laser intensity compensating for dynamic Stark shifts.
• Analytic calculations using strong-field phase matching show good agreement with experimental findings.

Conclusions:

• Laser pulse shaping provides effective control over two-photon absorption in the strong-field regime.
• The dynamic Stark shift plays a crucial role in maintaining two-photon resonance conditions.
• This study offers insights into controlling nonlinear atomic processes with tailored light fields.