FT-3: Magneto-optics and Magneto-plasmonics Part 2 P. Vavassori -IKERBASQUE, Basque Fundation for Science and CIC nanoGUNE Consolider, San Sebastian, Spain. MO-LPR phase Incident electric field E i LPR phase y H MO l ’ E i x Substrate P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Outline NANOANTENNAs COMBINING MAGNETIC AND PLASMONIC FUNCTIONALITITES ➢ Localized surface plasmons & Magneto-optical Kerr effects (MOKE): Introduction ➢ Physical picture and modeling ➢ LSPR-based sensing: Towards molecular sensing ➢ Photonics technology: control of the non-reciprocal light propagation MAGNETOPLASMONIC METAMATERIALS ➢ Surface lattice resonances in arrays of nanoantennae ➢ Arrays of elliptical nanoantennae ➢ Magnetoplasmonic gratings: arrays of antidots CONCLUSIONS P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Localized surface plasmon resonances (LSPRs) Localized surface plasmon resonances (LSPRs or LSPs) collective oscillations of conduction electrons in metallic nano structures. p d < l /2 1 G G F(t) 0.8 phase 0.6 0.4 a xx ( ) 0.2 ~ ( ) ~ x t x t a = 0 0 0.5 1 1.5 2 xx ( ) wavelength F t frequency d Small for excitation of a LSPR in the optical visible p range (air, glass … .) Ellipsoid a a a xx xy xz ~ a = a a a yx yy yz a a a zx zy zz |E| 2 [V 2 ·m 2 ] λ =717nm λ =663nm 12 (a) (b) Air -50 d=150nm 10 Au 8 h=32nm Subwavelength localization 0 6 Glass of electromagnetic energy 4 +50 2 [nm] 0 [nm] -100 0 +100 -100 0 +100 P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
EM field irradiated by an oscillating dipole q p Scattering and absorption remove energy from the incoming EM Absorption spectrometer = + ext sca abs a 2 sample sca Extinction Scattering ext a Im Wavelength Electric field lines due to an electric dipole oscillating vertically at the origin. Near the dipole, the field lines are essentially those of a static dipole. At a distance of the order of half wavelength or greater, the field lines are completely detached from the dipole P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Localized surface plasmon resonances (LSPRs) Scattering and absorption remove energy from the incoming EM Absorption = + ext sca abs spectrometer Extinction a 2 sca Scattering LSPR sample abs a Im Wavelength ext a Im Size Embedding medium λ λ =663nm Red-shift (b) Red-shift P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
LSPR as a damped harmonic oscillator ( ) ~ x t displacement 1.0 LSPR Phase ( p x) amplitude Phase ( p x) Im( a ) (a.u.) G a [ ] 0.5 G F Polarizability phase m 0.0 k Frequency wavelength ( ) ~ frequency x t Phase a [ ] Displacement 90 ° Displacement Displacement in anti-phase with E in phase with E out of phase with E P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Magnetoplasmonics Control of MO activity Control of plasmon properties (SPPs M K SPP → K’ SPP = K SPP K SPP ) G.Armelles , A. Cebollada , A. García-Martín , and M. Ujué González, Adv. Optical Mater. 2013 , 1 , 10 – 35 P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Hole-Mask Colloidal Lithography Adv. Mater. 19, 4297 (2007) ➢ Large areas ➢ Disordered distribution ➢ Insulating substrates Chalmers ➢ Low concentration to avoid interactions P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
E-beam lithography on glass Au nanoGUNE – Aalto – Stockholm – Singapore P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Negative e-beam lithography on glass nanoGUNE – Aalto – Stockholm – Singapore P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Ni nanoantennas Hole-Mask Colloidal Lithography (Ni disks on glass) Adv. Mater. 19, 4297 (2007) Disks 60x30 nm Disks 100x30 nm Disks 160x30 nm 350 nm 490 nm 650 nm Extinction Extinction Extinction LSPR LSPR LSPR P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Is the effect due to a LSPR? Scanning Near-Field Optical (SNOM) microscopy: amplitude and phase! In the NF, electric field is like the one produced by a static electric dipole + p /2 Exticntion - p /2 - p /2 + p /2 Intense E fields of opposite sign ( p out of phase) In press on Small Small 7 , 2341 (2011) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
A real LSPR? Scanning Near-Field Optical (SNOM) microscopy: amplitude and phase! spectrometer sample 60 nm 100 nm 160 nm In press on Small Small 7 , 2341 (2011) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Magneto-Optical Kerr effect configurations Magnetic characterization q K,F K,F P. Vavassori, APL 77 , 1605 (2000) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Spectroscopic Polar MOKE Modulation polarization E r technique for recording q K K x,y,z the longitudinal and polar H Kerr effects, both q and . photodiode H pol ref ( w,2w ) PEM ( w ) y sample lens E i E i SO Lock-in M x,y,z x 5mW (H) q (H) H 1nm lens E t sample pol lens (H) q (H) I 0 q F F AO w 2w lens Monochrom DC 5mW (400-800 nm) 1nm ref ( w , 2 w ) pol Lock-in q, H -H AO filter I PEM ( w ) (420-2000 nm) l < l l Supercontinuum pol Supercontinuum q Source l > l (420-2000 nm) photodiode Source (400-2000 nm) t P. Vavassori, APL 77 1605 (2000) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Polar MOKE spectra: polarization of reflected light linked to the LSPR position P-MOKE Extinction q K Experimental -3 3,0x10 350 nm Disks 60 nm Pol S -3 q 2,0x10 Extinction -3 1,0x10 Angle (rad) K 0,0 -3 -1,0x10 Pol P LSPR -3 -2,0x10 q -3 -3,0x10 450 500 550 600 650 700 750 800 Experimental Wavelength (nm) P. Vavassori, Appl. Phys. Lett. 77 , 1605 (2000) -3 4,0x10 Disks 100 nm 490 nm Pol S q -3 2,0x10 Angle (rad) Extinction Refence Ni film 0,0 Pol P -3 -2,0x10 q LSPR Ni film q k 2.0 4.0 -3 -4,0x10 k 450 500 550 600 650 700 750 800 Angle (mrad) Experimental 1.0 Wavelength (nm) 2.0 -3 5,0x10 650 nm Disks 160 nm 650 nm Pol S 0.0 q 0.0 -3 2,5x10 Extinction Ni film Angle (rad) -1.0 -2.0 450 600 750 900 0,0 LSPR Wavelenght (nm) Film – no crossings in the visible range -3 Pol P -2,5x10 q ➢ Maximum of q K and crossing -3 -5,0x10 450 500 550 600 650 700 750 800 Wavelength (nm) of K follow the LSPR position Phys. Rev. Lett. 111 , 167401 (2013) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Simple physical picture: two coupled damped harmonic oscillators!!! 1 Phase ( p ) 0.8 Amplitude 0.6 0.4 0.2 0 0 0.5 1 1.5 2 Damped harmonic oscillator Phase contribution ➢ Damped H.O.: confinement ➢ S.O. coupling: material property Fundamental hypothesis here: linear and perturbative regime P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Induced electric dipoles 1. Oscillator along x M p x = a xx E 0 p x = c xx E x i = ( – m ) E x i P MO E i = E 0 – E x d E x 2. S.O. Coupling S.O. = c yx E x i = yx E x i p y a S.O. / c yy = p y S.O. /( – m ) p E y S.O. = p y y = yx yy ( ) 2 − p 3. Oscillator along y x m Gives the polarization of the far-field radiated p y = a yy E y i ( a yy yx ) / ( – m ) in the z-direction by these two mutually S.O. = E x orthogonal oscillating electric dipoles ➢ MO enhancement depends only on a yy (shape can improve enhancement) ➢ Relative phase on both a yy and yx P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
Simple physical picture: two S.O. coupled damped harmonic oscillators: relative phase ➢ Damped H.O.: confinement E(z, t) Polarization of the radiated field ~ ➢ S.O. coupling: material property p y ~ ~ = = − = p p y x ~ z p x yx = + a ( ) yy − 2 m = 0 K 0< < p/2 Kerr = p/2 q K = 0 K Wavelength p/2 < < p S.O. a yy p y = yx = p ( ) 2 − Faraday p x m Phys. Rev. Lett. 111 , 167401 (2013) P. VAVASSORI European School on Magnetism (ESM-2018), Krakow 17-28 September 2018
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