Atoms in high intensity mid-infrared pulses

Abstract

The recent development of intense, ultrashort, table top lasers in the mid-infrared opens new avenues for research in strong field atomic physics. Electrons submitted to such radiation acquire huge quiver energies, even at moderate intensity and interesting properties arise: first, the wavelength offers a convenient experimental knob to tune the ionisation regime by controlling the Keldysh parameter. Second, many processes like above-threshold ionisation or high harmonic generation, whose characteristics depend directly on this energy, can be pushed to unprecedented limits. Third, the wavelength controls the spectral phase of the harmonics and hence the possibility to improve the generation of pulses in the attosecond regime. Recent studies of rare gas and alkali atoms' photoelectron spectra and harmonic generation at 2 and 3.6 μm have begun to confirm the theoretical predictions. However, unexpected features have also been found showing that strong field interaction still keeps some secrets after more than 40 years of investigation.

Keywords:

• multiphoton ionisation
• above-threshold ionisation
• high harmonic generation
• attosecond pulses

Acknowledgement

The authors are grateful for the dedication of The Ohio State University group for the investigations presented in this review. In particular, we thank Cosmin Blaga, Fabrice Catoire, Phil Colosimo, Gilles Doumy, Anne Marie March, Jennifer Tate and Jonathan Wheeler. We also acknowledge the fruitful collaboration with Professor Gerhard Paulus at the University of Jena. LFD acknowledges support from the Edward and Sylvia Hagenlocker chair endowment. The authors acknowledge support from the US Department of Energy, Basic Energy Sciences and the National Science Foundation.