Quantum coherent control of free electron wavefunction using ponderomotive potential of optical fields

Electron microscopy and diffraction allow to study structure of materials with unprecedented spatial resolution. When combined with ultrashort laser pulses, the time-resolved imaging with electron beams enable dynamical visualization of phase transitions or chemical reactions. The electron pulses are typically generated by photoemission of electrons from a cathode. The pulse duration is fundamentally limited by the duration of the photoemission laser pulse. However, the temporal coherence of the generated electron wavepacket is typically much shorter than the pulse duration. This fact limits the use of such wavepackets in measurements relying on quantum phase coherence of the electrons over extended time scales. Spatio-temporal control of the phase of electron wavepacket on time scales comparable to the coherence time thus can bring novel possibilities for applications in quantum electron microscopy or ultrafast electron holography.

In this thesis, novel scheme for quantum coherent control of the wavefunction of freely propagating electron wavepackets will be theoretically and experimentally studied. The scheme is based on the interaction of electron wavepacket with ponderomotive potential of an optical travelling wave generated by two laser fields at different frequencies [1,2]. When the temporal period of the optical travelling wave is shorter than the temporal coherence length of the electron wavepacket, population of energy sidebands of electrons can be coherently manipulated by controlling the strength of the interaction [3]. Theoretical description of the interaction will be based on the path integral representation of the wavefuction. We will consider the interaction with spatially- and temporally-shaped pulses and propose experiments, which will be performed in collaboration with the group of prof. Hommelhoff from FAU Erlangen-Nürnberg.

References:

[1] M. Kozák, et al., Inelastic ponderomotive scattering of electrons at a high-intensity optical travelling wave in vacuum, Nat. Phys. 14, 121-125 (2018).
[2] M. Kozák, et al., Ponderomotive generation and detection of attosecond free-electron pulse trains, Phys. Rev. Lett. 120, 103203 (2018).
[3] A. Feist, et al., Quantum coherent optical phase modulation in an ultrafast transmission electron microscope, Nature 521, 200-203 (2015).