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. Author manuscript; available in PMC: 2015 Aug 2.
Published in final edited form as: Nat Commun. 2015 Feb 2;6:6150. doi: 10.1038/ncomms7150

Figure 1. LPR phase-sensitivity in the transmitted light polarization.

Figure 1

a. When an incident light beam hits a ferromagnetic nanoantenna, the conduction electrons inside the nanostructure oscillate driven by the electric field Ei. These Ei-driven oscillations can be modeled as a damped spring-mass harmonic oscillator. A LPR is induced at a specific photon wavelength λ*, yielding a peak in the extinction spectrum (I0−It)/I0 = 1-(Et/Ei)2, displayed in the top panel. b. If the nanoantenna is magnetized perpendicularly to the surface plane, a MO-activity is turned on inducing a second MO-coupled LPR (MO-LPR) orthogonal to that directly driven by Ei. In a circular nanoantenna the MO-LPR resonates at the same λ*. The simultaneous excitation of LPR and MO-LPR induces an elliptical polarization ε of the transmitted field Et20,21. The null condition ε = 0 is generated at a desired λε (in general λε ≠ λ*) simply through engineering of the size of the circular nanoantenna21,34,35. Measurement of λε provides a precise phase sensitive detection of the LPR position. The top panel displays typical Δε spectrum (red-line), as well as the 1/|Δε| spectrum (blue-line) and its resonance at λε. The close-up view of the 1/|Δε| spectrum around λε shown in the inset features a very narrow FWHM (1.7 nm). c. Similarly to the case described in (b), the concerted action of the simultaneously excitated LPR and MO-LPR can be exploited to actively manipulate the reflected light’s polarization inducing the condition ε = 0 at a desired λ′ε. In general λ′ε ≠ λε since in this case also the additional phase introduced by the substrate reflectivity contributes to the polarization of the reflected field Er. As in transmission geometry, the detection of λ′ε provides precise phase sensitive detection of the LPR position. The top panel displays typical Δε spectrum (red-line), as well as the 1/|Δε| spectrum (blue-line) and its resonance at λ′ε. The close-up view of the 1/|Δε| spectrum around λ′ε shown in the inset features a very narrow FWHM (< 1.7 nm). Both in transmission and reflection, the sensitivity increases further by measuring the magnetic field- induced variation Δε as ε reverses its sign upon inverting H (see Supplementary Fig. 2).