Dear Steven and Meep users,
I want to monitor the time evolution of electric field at a fixed point in
vacuum. But I can not understand the results from the simulation.
Firstly, I set two monitors in the simulation. One is close to the source, and
the other is far from the source. However, the amplitude of two electric
fields is different each other. The amplitude of the electric field closed to
the source is larger than that of far from the source. In my opinion, the
amplitude of two electric fields should be equal as propagating in vacuum.
Meanwhile, the amplitude of two electric fields is far less than 1.
Secondly, when I zoom in the two sides of the electric field (at the beginning
and the end of time), I find that there is some noise. If I change the
Gaussian source into continuous source, the result is worse. I think that the
two sides should be smooth to get a perfect simulated result. What is the
reason? How can I improve it? Figure 2 and figure 3 give the results.
I attached the results in the previous email, but the figures are too big to
post them. Attachment is my ctl file. Thanks a lot.
Best,
Shuqi
(reset-meep)
(define-param unit 100e-9) ; base unit in meters (1e-9 = 1 nm)
(define-param c 299792458) ; the speed of light in vacuum (m/s)
(define-param lam 785e-9) ; free space wavelength (meters)
(define lamu (/ lam unit)) ; wavelength in base units
; Some parameters to describe the geometry:
(define-param len 1.16) ; length of square
(define-param dpml 2) ; PML thickness
(define-param pad 0.5) ; the distance from pml
; The lattice dimensions
(define sx (+ len gap)) ; size of cell in x direction
(define sy (+ len gap)) ; size of cell in y direction
(define sz 6) ; size of cell in z direction
(set! geometry-lattice (make lattice (size sx sy sz)))
(set-param! resolution 20)
; Set Geometry
(set! geometry '())
(set-param! k-point (vector3 0 0 0)) ; set periodic boundary condition
(set! pml-layers (list (make pml (thickness dpml) (direction
Z))))
; Set Source
(define fcen (/ unit lam)) ; source center frequency
(define-param pw 2e+14) ; free space pulse width (in frequency)
(define df (/ (* pw unit) c)) ; pulse width in Meep Unit
(set! sources (list
(make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Ex)
(center 0 0 (+ (/ sz -2) dpml pad))
)))
(run-until 300
(to-appended "air-point1" (in-volume (volume (center 0.1 0.2 (- (/ sz 2)
dpml pad)) (size 0 0 0))
output-efield-x))
(to-appended "air-point2" (in-volume (volume (center 0.1 0.2 (+ (/ sz -2)
dpml pad 0.5)) (size 0 0 0))
output-efield-x))
)
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