Speaker
Description
Inelastic electron-light interaction in the TEM enables the imaging of optical near fields through techniques like photon induced near field electron microscopy (PINEM). The interaction of free electrons with localized, time-dependent electric fields modulates the longitudinal wave function and gives rise to a spectral comb consisting of characteristic sidebands separated by multiples of the photon energy [1-4]. Amplitude information of the field can be extracted from the width of the spectral comb. However, obtaining phase information requires more sophisticated measurement techniques, e.g. with two sequential interactions [5,6].
Here, we demonstrate holographic measurements on optical near fields achieved through a superposition of parallel, inelastic electron-light interactions in scanning transmission electron microscopy (STEM) with single-electron probes spatially separated in two different paths [7,8]. Using an electron spectrometer in an energy dispersive mode, we observe the electron interference pattern as a function of energy, enabling us to simultaneously recover amplitude and phase of the near field.
In a second step, we record holograms without using a spectrometer. We demonstrate how the interference visibility in this scenario provides information on the amplitude of the two inelastic interactions. This method offers the unique advantage that it does not depend on the energy resolution of the spectrometer and is therefore not limited to excitations with energies larger than or equal to the initial energy spread of the electron beam.
In conclusion, we demonstrate a STEM-based holography approach tailored to the characterization of coherent inelastic scattering. This versatile method allows for time-resolved imaging of optical near fields when combined with a spectrometer and spectrometer-free measurements of field distributions on the nanoscale.
[1] B. Barwick et al., Nature 462, 902–906 (2009).
[2] F.J. García de Abajo et al., Nano Letters 10, 1859–1863 (2010).
[3] S.T. Park et al., New Journal of Physics 12, 123028 (2010).
[4] A. Feist et al., Nature 521, 200–203 (2015).
[5] D. Nabben et al., Nature 619, 63–67 (2023).
[6] J.H. Gaida et al., Nature photonics 18, 509–515 (2024).
[7] F.S. Yasin et al., Journal of Physics D: Applied Physics 51, 205104 (2018).
[8] F.S. Yasin et al., Nano Letters 18, 7118–7123 (2018).