Optical coherence transfer by free electrons and its effects on CL emission
Ofer Kfir Valerio Di Giulio a b c, Valerio Di Giulio c, F. Javier García de Abajo c d, Claus Ropers b e
a Tel Aviv University, School of Electrical engineering, Tel Aviv 69978, Israel
b Max Planck Institute for Biophysical Chemistry (MPIBPC), Göttingen 37077, Germany
c ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
d ICREA - Institució Catalana de Recerca i Estudis Avançats, Passeig de Lluís Companys 23, 08010 Barcelona, Spain
e University of Göttingen, IV. Physical Institute, Göttingen, Germany
Proceedings of Electron Beam Spectroscopy for Nanooptics 2021 (EBSN2021)
Online, Spain, 2021 June 14th - 15th
Organizers: Mathieu Kociak and Nahid Talebi
Oral, Ofer Kfir Valerio Di Giulio, presentation 036
Publication date: 8th June 2021

Cathodoluminescence (CL) offers intriguing coherence properties. Originating from a spontaneous process in a deep subwavelength region, it is generally temporally incoherent, albeit with an exquisite spatial coherence. Thus, CL can be interfered with itself spatially and spectrally1,2, but not with an external laser field. Coherent mixing with a reference laser at a controllable phase delay would offer novel opportunities in CL physics.

 

This talk discusses the concept of coherent CL emission based on free electron beams modulated by PINEM (photon-induced nearfield electron microscopy)3. In particular, we present CL-emission effects linked to the transfer of optical phase information by an electron, rather than by light waves4,5. On one hand, the emitted CL power is independent of the PINEM modulation, hence, observing coherences require far-field interference with a reference laser. The fundamentally different nature of the electron facilitates nontrivial emission properties. For example, even a single electron exhibits inherent nonlinearity, as it can transfer coherences at discrete harmonics of the laser frequency. Additionally, the coupling of the coherent emission to radiation varies with the electron propagation as a result from the electron’s relativistic dispersion. The suppression or enhancement of the emitted power requires a different concept. We show that illuminating the reference laser directly at the sample allows the optical scattering and the coherent CL emission to interfere controllably. In the case of CL from a PINEM-modulated electron, that can lead to the suppression of the emission at the harmonic frequencies of the PINEM-driving laser.

 

We believe that the presented work sets the path for coherent control of optical excitations and opens new routes toward the realization of quantum-state tomography of light states with nanoscale precision.    

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