When an atom or molecule is exposed to a strong laser field, an electron wave packet can be ionized through tunneling. The ionized electron wave packet may be driven back to parent ion, result in an interesting phenomenon called strong field photoelectron holography. By analogy to the conventional optical holography, the strong field holography is recognized as the interference of tunneling electron wave packets drifting directly to the detector (reference wave) and those undergoing rescattering by the parent ion (signal wave). Generally, it is the near-forward rescattering electrons that record the structure information of the target. For this near-forward rescattering process, the electrons do not catch much information about the core because of the very soft recollision with the core. In order to gain more information of the target, one can use the hologram from the direct and backscattering electrons, i.e., the backscattering photoelectron hologram (BPH). However, the BPH is usually very difficult to be identified in the experiment.

The ultrafast optics group led by Prof. Peixiang Lu presents a novel approach to reveal backscattering photoelectron hologram using orthogonal two-color fields. By carefully adjusting the relative phase of the two-color field, the BPH is effectively separated from other interferences in the photoelectron momentum spectra and thus the BPH is unambiguously identified. This takes a significant step to time-resolved imaging of the attosecond dynamics with strong-field photoelectron holography.

This work is published on Opt. Express Opt. Express Vol. 24, No. 21, 23697 (2016). This work was supported by the National Natural Science Foundation of China under Grants No. 11234004, No. 11404123 and No. 61275126, the 973 Program of China under Grant No. 2011CB808103, and the Natural Science Foundation of Hubei Province under Grant No. 2014CFB174.

Figure The photoelectron momentum distribution and the backscattering photoelectron hologram in orthogonal two-color fields.