In
this work, we introduce a radically new approach for achieving
doubly resonant light-to-sound conversion with radiofrequency waves,
namely, electromagnetic waves in the range of 1–100 MHz. By
taking the profit from recently published metamaterials exhibiting
plasma-like responses in the radio range, we introduce the concept
of “radioplasmonics” that deals with localized surface
plasmons in the radio regime. In analogy with conventional plasmonics,
radioplasmonics can be exploited to design microtransducers that effectively
convert radio-waves into heat through resonant electromagnetic absorption.
Then, by tuning the Young’s modulus of the transducers, we
can achieve resonant acoustic vibrations in the same range of frequencies
as the plasmonic resonances. In this way, plasmonic heating is converted
into resonant thermo-acoustic expansion and its consequent generation
of pressure waves. The latter can then be used for ultrasound imaging.
We show that, in this double resonance framework, the intensity of
the generated acoustic waves is above the current detection level
under realistic conditions. The importance of using the radio range
is related to its ability to deeply penetrate water and biological
tissues. Hence, the proposed approach paves the way to the first total-body
thermo-acoustic imaging able to reach a single-cell resolution.
In this paper we calculate the optical forces and torques caused by the presence of a sizable magneto-optical effect. We find a conservative force proportional to the gradient of the spin density of the light field and an extinction force proportional to the helicity of the light field. The conservative interaction allows for a spin-selective, magnetic field based Stern-Gerlach experiment, capable of differentiating between right and left circular polarizations. We also prove that by using a spinless linearly polarized plane wave, the magneto-optical effect allows for the existence of a permanent nonreciprocal torque, proportional to the intensity of the light field.
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