Aushell cavity mode Mie calculations cavity mode 700

Au-shell cavity mode - Mie calculations cavity mode 700 nm cavity mode 880 nm Rcore = 228 nm Rtotal = 266 nm t. Au = 38 nm medium = silica 880 nm = 340 THz 1

Finite Difference Time Domain method Step 1: Excitation Plane wave excitation on and off resonance stores some energy in particle Step 2: Relaxation Particle oscillates, reemitting at its resonance frequency Step 3: Fourier Transform Fast Fourier transform of the relaxation E(t) to generate frequency spectrum ky Ex 2

Snapshots - Au shell (R=266 nm, t. Au = 38 nm) in silica box (1. 5 x 1. 5 μm 2) +2 excitation off-resonance at 150 THz (2 μm) +1 E-field monitor in center 0 Ex 335 THz (895 nm) -1 Fast Fourier Transform -2 p=1. 3 x 1016 rad/s =1. 25 x 1014 rad/s d=9. 54 3

Snapshots - Au shell (R=266 nm, t. Au = 38 nm) in silica box (1. 5 x 1. 5 μm 2) +2 excitation off-resonance at 150 THz (2 μm) Electric field intensity max= 6. 5 at center 5 +1 0 -1 -2 Ex cavity mode! excitation on-resonance at 335 THz (895 nm) 0 4

Cavity parameters • Quality factor Q=35 • The maximum field enhancement within the core amounts to a factor of 6. 5 • The mode volume V=0. 2 ( /n)3 … 102 -103 smaller than that in micordisc/microtoroid WGM cavities • A characteristic Purcell factor – assuming homogeneous field distribution in the cavity core and =895 nm

Cavity optimization A characteristic Purcell factor assuming homogeneous field distribution in the cavity core, =895 nm and Q=150:

Cavity mode is tunable - T-matrix vs FDTD calculations Penninkhof et al, JAP 103, 123105 (2008) 7

Cavity mode is tunable by shape - oblate Au shell spheroid aspect ratio =2. 5 T / 240 THz L / 410 THz 8