Photoemission Electron Microscopy for Analysis of Dielectric Structures and the Goos-Hänchen Shift

Abstract

Photoemission Electron Microscopy (PEEM) is a versatile tool that relies on the photoelectric effect to produce high-resolution electron images. Ultrafast pulse lasers allow for multi-photon PEEM where multiple visible or IR photons excite a single electron in a nonlinear process. The photoelectron yield in both cases is related to the near-field region of electromagnetic fields at the surface of the sample. We use this ability here to analyze wave propagation in a linear dielectric waveguide with wavelengths of 410 nm and 780 nm. The propagation constant of the waveguide can be extracted from interference patterns created by light propagating in the waveguide and incident light. Various properties like the polarization dependence of the propagation can be analyzed. The electromagnetic field interaction at the boundaries can then be deduced, which is essential to understand power flow in wave guiding structures. These results match well with simulations using finite element techniques as well as electromagnetic theory.

Localized Photoemission in Triangular Gold Antennas

“…Reprinted with permission from Photoemission Electron Microscopy for Analysis of Dielectric Structures and the Goos-Hänchen Shift, by Theodore Axel Stenmark, PortlandState University, 2016[30].Multiphoton PEEM (nP-PEEM)-a non-linear imaging process utilizing multiphoton electron emission-can be used in place of traditional single-photon PEEM imaging. The energy of the incident light can be varied within the fundamental frequency range of the laser and to higher-order harmonics, enabling the observation of a widerange of materials and optical effects.…”

“…Due to the non-linearity of the multi-photon emission process, a modest increase in the source intensity could produce a significant increase in photoemission from the sample. The work function of most interesting materials prohibits the use of 1P-PEEM for the visible and IR ranges, but the high intensities of ultrafast pulsed lasers can be enough to overcome these energy barriers and enable multi-photon PEEM imaging[30].In addition to the necessity for nP-PEEM for certain materials and wavelength ranges, the non-linear response of multi-photon excitation provides strong image contrastthrough the imaging technique's sensitivity to variations in the local photon density at the surface of the sample. Image contrast in general in PEEM arises from the spatial distribution of photoemitted electrons from the sample.…”