1
Au-shell cavity mode - Mie calculations
Rcore = 228 nm
Rtotal = 266 nm
tAu = 38 nmmedium = silica
cavity mode
700 nm
cavity mode
880 nm
880 nm = 340 THz
2
Finite Difference Time Domain method
Step 1: Excitation
ky
Ex
Step 2: Relaxation Step 3: Fourier Transform
0 200 400 600 800 10000.000
0.005
0.010
0.015
0.020
0.025
0.030
Frequency (THz)
Am
plitu
de
Plane wave excitation on and off resonance stores some energy in particle
Particle oscillates, reemitting at its resonance frequency
Fast Fourier transform of the relaxation E(t) to generate frequency spectrum
3
Snapshots - Au shell (R=266 nm, tAu = 38 nm) in silica box (1.5x1.5 μm2)
excitation off-resonanceat 150 THz (2 μm)
-2
-1
0
+1
+2
0 200 400 600 800 1000
FF
T o
f Ex
Frequency (THz)
0 20 40 60 80 100
x-co
mpo
nent
of E
-fie
ld (
a.u.
)
time (fs)
335 THz(895 nm)
Ex
Fast Fourier Transform
E-field monitor in center
p=1.3x1016 rad/s
=1.25 x1014 rad/s
d=9.54
4
Snapshots - Au shell (R=266 nm, tAu = 38 nm) in silica box (1.5x1.5 μm2)
excitation off-resonanceat 150 THz (2 μm)
excitation on-resonanceat 335 THz (895 nm)
cavitymode!
Electric field intensity max= 6.5 at center
0
5
-2
-1
0
+1
+2
Ex
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 than that in micordisc/microtoroid WGM cavities
• A characteristic Purcell factor – assuming homogeneous field distribution in the cavity core and =895 nm
134
33
2
V
Q
nP
Cavity optimization
544
33
2
V
Q
nP
A characteristic Purcell factor assuming homogeneous field distribution in the cavity core, =895 nm and Q=150:
7
Cavity mode is tunable - T-matrix vs FDTD calculations
Penninkhof et al, JAP 103, 123105 (2008)
8
Cavity mode is tunable by shape - oblate Au shell spheroid
aspect ratio =2.5
L / 410 THz
T / 240 THz