2012/08/22 by S Winnerl, S. Winnerl, R Hubrich +7 · 56 citations
Engineering · Materials Science · Physics and Astronomy · #Beam (structure) #Electromagnetic field #Field (mathematics) #Longitudinal field #Metamaterials and Metasurfaces Applications #Phase (matter) #Plasmonic and Surface Plasmon Research #Terahertz radiation #Terahertz technology and applications #Transverse field #Transverse plane #physics.optics
paper · pdf · doi:10.1088/1367-2630/14/10/103049
published in New Journal of Physics 14(10), 103049 (IOP Publishing)
arxiv created 2012/08/22 · openalex publication_date 2012/10/30 · arxiv updated 2015/06/11 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz (THz) beams of radial and linear polarization. Employing electro-optic detection, which is phase sensitive, allows one to selectively detect longitudinal and transverse field components. A phase shift of π /2 between the transverse and longitudinal field components is revealed. This phase shift is of universal nature, as it does not depend on the mode, frequency and focusing conditions. We show that the universal phase relation is a direct consequence of the divergence-free nature of electromagnetic waves in vacuum. In the experiments, we observe the phase shift of π /2 for all frequency components of single-cycle THz radiation pulses of both radial and linear polarization. Additionally, we show that the longitudinal field of a radially polarized THz beam has a smaller spot size as compared with the transverse field of a linearly polarized beam that is focused under the same conditions. For field-sensitive measurements this property can be exploited even for moderate focusing conditions. Furthermore, the phase-sensitive detection of longitudinal electromagnetic fields opens up new possibilities to study their interaction with electronic excitations in semiconductor nanostructures.