We study magnetic and electric hotspots in the gaps of nanoparticle dimers and trimers composed of hollow silicon nanoparticles. We find that the hollow size markedly influences the overall shape of the field enhancement, in particular, the peak magnitude and the peak position. The peak shifts about 100−200 nm as the hollow size varies. Tuned magnetic hotspots allow one to better enhance the Raman optical activity and circular dichroism of molecules, the interaction of light and nanomagnets, and so on.

We study electric and magnetic hotspots in the gap between hollow InSb microspheres forming dimers and trimers. The outer radius, core volume fraction, distance, and temperature of the microspheres can be chosen to achieve field enhancement at a certain frequency corresponding to the transition between energy levels of a molecule placed in the gap. For example, utilizing 80 μ m radius spheres at a gap of 2 μ m held at a temperature of 295 K, allow electric field intensity enhancements of 10–2880 and magnetic field intensity enhancements of 3–61 in the frequency window 0.35–1.50 THz. The core volume fraction and the ambient temperature affect the enhancements, particularly in the frequency window 1.5–2 THz. Electric and magnetic hotspots are promising for THz absorption and circular dichroism spectroscopy.

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Overshadowed by the electric dipole ones, the magnetic dipole transitions of a quantum emitter are hard to probe. This can be remedied by using pure magnetic hotspots, which host strong magnetic but quite weak electric fields in a subwavelength region. Utilizing the multiparticle Mie theory, we demonstrate pure magnetic hotspots via hollow silicon nanoparticles arranged in a ring configuration and illuminated by Bessel cylindrical vector beams. Normalized local field admittances of about [Formula: see text]–[Formula: see text] and magnetic field enhancements of about 10–30 are achievable. Moreover, the peak of the magnetic field enhancement can be shifted about [Formula: see text] nm via the hollow size. In other words, the pure magnetic hotspot can be optimized for a particular magnetic dipole transition.