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## linear-chirped pulse planewave with higher frequencies at the front (down-chirp)
import meep as mp
import numpy as np
resolution = 40
dpml = 2
pml_layers = [mp.PML(thickness=dpml,direction=mp.X)]
sx = 40
sy = 6
cell_size = mp.Vector3(sx+2*dpml,sy)
v0 = 1.0 # pulse center frequency
a = 0.2 # Gaussian envelope half-width
b = -0.5 # linear chirp rate (positive: up-chirp, negative: down-chirp)
t0 = 15 # peak time
chirp = lambda t: np.exp(1j*2*np.pi*v0*(t-t0)) * np.exp(-a*(t-t0)**2+1j*b*(t-t0)**2)
sources = [mp.Source(src=mp.CustomSource(src_func=chirp),
center=mp.Vector3(-0.5*sx),
size=mp.Vector3(y=sy),
component=mp.Ez)]
sim = mp.Simulation(cell_size=cell_size,
boundary_layers=pml_layers,
resolution=resolution,
k_point=mp.Vector3(),
sources=sources,
symmetries=[mp.Mirror(mp.Y)])
sim.run(mp.in_volume(mp.Volume(center=mp.Vector3(), size=mp.Vector3(sx,sy)),
mp.at_every(2.7, mp.output_efield_z)),
until=t0+50)
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