Photon-induced near-field electron microscopy: Mathematical formulation of the relation between the experimental observables and the optically driven charge density of nanoparticles
Photon-induced near-field electron microscopy (PINEM) enables the visualization of the plasmon fields of nanoparticles via measurement of photon-electron interaction [S. T. Park et al., New J. Phys. 12, 123028 (2010)]. In this paper, the field integral, which is a mechanical work performed on a fast electron by the total electric field, plays a key role in understanding the interaction. Here, we reexamine the field integral and give the physical meaning by decomposing the contribution of the field from the charge-density distribution. It is found that the "near-field integral" (the near-field approximation of the field integral) can be expressed as a convolution of the two-dimensional projection of the optically driven charge-density distribution in the nanoparticle with a broad radial response function. This approach, which we call the "convolution method," is validated by applying it to Rayleigh scattering cases, where previous analytical expressions for the field integrals in near-field approximations are reproduced by the convolution method. The convolution method is applied to discrete dipole approximation calculations of a silver nanorod, and the nature of the induced charge-density distributions of its plasmons is discussed.
Additional Information© 2014 American Physical Society. Received 17 September 2013; revised manuscript received 16 October 2013; published 31 January 2014. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Center for Physical Biology funded by the Gordon and Betty Moore Foundation. The authors wish to thank the referees for the thorough review and helpful comments. S.T.P. would like to thank Dr. Giovanni M. Vanacore, Dr. Timothy D. Scarborough, and Dr. J. Spencer Baskin for fruitful discussions.
Published - PhysRevA.89.013851.pdf