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