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174 5 Near Field

(a) Initial condition (b)

Initial excitation
T+DT
1500 nm
Magnetic field
y
500 nm
Electric field
z x 100 nm
25 nm
Boundary
conditions
Incident wave
Results

Fig. 5.5. Calculation process for FDTD (a), and computational domain for calcu-
lation (b)

TM field
75 nm
E x
Boundary

0 nm
-250 nm 250 nm
Aperture
75 nm
E y

Boundary
0 nm
-250 nm 250 nm
Aperture
Fig. 5.6. Numerical result indicating that the electric evanescent field is enhanced
at the edge and decays rapidly

Example 5.2. (1) Show the time-step dependence on the electric field intensity
E x for Example 5.1.
(2) Show the round-trip number dependence on the electric field E x at 20 nm
above the aperture for Example 5.1.