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We demonstrate experimentally the detection of magnetic force at optical frequencies, defined as the dipolar Lorentz force exerted on a photoinduced magnetic dipole excited by the magnetic component of light. Historically, this magnetic force has been considered elusive since, at optical frequencies, magnetic effects are usually overshadowed by the interaction of the electric component of light, making it difficult to recognize the direct magnetic force from the dominant electric forces. To overcome this challenge, we develop a photoinduced magnetic force characterization method that exploits a magnetic nanoprobe under structured light illumination. This approach enables the direct detection of the magnetic force, revealing the magnetic nearfield distribution at the nanoscale, while maximally suppressing its electric counterpart. The proposed method opens up new avenues for nanoscopy based on optical magnetic contrast, offering a research tool for all-optical spin control and optomagnetic manipulation of matter at the nanoscale.

Surface-enhanced coherent anti-Stokes Raman scattering (SE-CARS) takes advantage of surface plasmon resonances supported on metallic nanostructures to amplify the coherent Raman response of target molecules. While these metallic antennas have found significant success in SE-CARS studies, photoinduced morphological changes to the nanoantenna under ultrafast excitation introduce significant hurdles in terms of stability and reproducilibty. These hurdles need to be overcome in order to establish SE-CARS as a reliable tool for rapid biomolecular sensing. Here, we address this challenge by performing molecular CARS measurements enhanced by nanoantennas made from high-index dielectric particles with more favorable thermal properties. We present the first experimental demonstration of enhanced molecular CARS signals observed at Si nanoantennas, which offer much improved thermal stability compared to their metallic counterparts.

Photo-induced force microscopy (PiFM) is a scan probe technique that offers images with spectroscopic contrast at a spatial resolution in the nanometer range. PiFM utilizes the non-propagating, enhanced near field at the apex of a sharp tip to locally induce a polarization in the sample, which in turn produces an additional force acting on the cantilevered tip. This photo-induced force, though in the pN range or less, can be extracted from the oscillation properties of the cantilever, thus enabling the generation of photo-induced force maps. Since its inception in 2010, the PiFM technique has grown into a useful nano-spectrocopic tool that has expanded its reach in terms of imaging capabilities and applications. In this review, we present various technical implementations of the PiFM approach. In addition, we discuss the physical origin of the PiFM signal, highlighting the contributions from dipole-dipole forces as well as forces that derive from photo-thermal processes.