Measuring light is often a rather simple and straight-forward task. Actually, this is only true if the parameters of light to be measured are intensity or color. By design, cameras are built for exactly this purpose of measuring the spatial distribution of light’s intensity or brightness, with color information retrieved by adding spectral filters. In a similar manner, the oscillation direction of light waves, the so-called polarization, can also be accessed following the same strategy, i.e., by adding (polarization) filters to a standard camera. But measuring how synchronous or asynchronous light waves oscillate, or, in other words, experimentally retrieving phase information of a light field, is usually a more sophisticated task because a phase measurement normally requires a comparison of the waves with a reference or with each other. Speaking of difficult tasks, the aforementioned measurements are usually restricted to the electric field of light, its intensity, oscillation direction and phase, while the magnetic field of light waves is naturally and inevitably harder to access. To add even more levels of complication, the situation becomes increasingly more sophisticated if the light field to be analyzed or utilized is strongly spatially confined, for instance by tight focusing with a lens, a configuration routinely used in optical microscopy, nanometrology or nanofabrication. The field turns three-dimensional while exhibiting features varying on deep sub-wavelength length-scales. Naturally, all standard measurement techniques of intensity, polarization and phase will fail in this regime. However, the spatial distributions of such parameters of light, both for the electric and magnetic field distributions, encode important information about the environment the electromagnetic fields interacted with. Hence, their experimental characterization at the nanoscale plays a pivotal role in many applications, from microscopy to sensing and beyond.
In a recent publication, Jörg Eismann and Peter Banzer now present, both experimentally and theoretically, a novel and powerful technique, allowing for the highly precise measurement of the intricate structure of light’s properties at the nanoscale. In particular, their technique enables the direct retrieval of full-field information for both the electric and the elusive magnetic field components, revealing their differences in terms of field distributions. The backbone of this method is a nanoparticle used as a probe locally interacting with the field, combined with a clever analysis of the scattered light. The results were published in ACS Photonics.
This study opens new avenues for investigating the electric and magnetic fields independently but simultaneously with outstanding spatial resolution, providing access to hidden nanoscale wave phenomena in general while also enabling quantitative utilization of nanoscale fields in a variety of different applications, ranging from ultra-precise nanometrology to imaging.
Reference:
Jörg S. Eismann and Peter Banzer, Nanoscale Vectorial Electric and Magnetic Field Measurement, ACS Photonics Article ASAP; DOI: 10.1021/acsphotonics.4c01831
Contact:
Peter Banzer; Optics of Nano and Quantum Materials (website)