The reflection of a gaussian pulse
Closed this issue · 4 comments
I tried to get a left-handed circularly polarized Gaussian light to hit the plasma target at an oblique Angle of 30 degrees, but many reflected stray light that confused me very much(stray light has been marked in a red box).I really appreciate your help.
Here is the input deck.
begin:constant
# laser
input_las_a_0 = 1.0e-3
I_focus = 1.37e18 * (input_las_a_0)^2 #W/cm^2
las_lambda = 1.0 * micron
las_k = 2.0 * pi / las_lambda
las_omega = 2.0 * pi * c / las_lambda
las_period = 2.0 * pi / las_omega
w0 = 5 * micron
t0 = 10 * las_period
t0_x = 25 *las_period
theta = pi/3
theta_pla = pi/2 - theta # angle of inclination of plasma
x_spot = 15/tan(theta_pla) * micron
x_R = pi * w0^2 / las_lambda
w_bnd = w0 * sqrt(1.0 + (x_spot/x_R)^2)
gouy = atan(x_spot/x_R)
phasey = 0
phasez = pi/2
# plasma
n_crit = critical(las_omega)
n_plate = 0.9 * n_crit
#plasma density profile of plasma plate
x_left = 0
x_right = 30.0/tan(theta_pla) * micron
y_up = tan(theta_pla) * x
y_down = tan(theta_pla) * (x - 2/sin(theta_pla) * micron)
z_front = 15.0 * micron
z_back = -z_front
end:constant
begin:control
# final time of simulation
t_end = 100 * las_period
# nsteps = 0
# size of domain
nx = 60*10
ny = 60*10
nz = 30*10
x_min = 0
x_max = 60 * micron
y_min = 0 * micron
y_max = 60 * micron
z_min = -15 * micron
z_max = -z_min
stdout_frequency = 50
end:control
begin:boundaries
bc_x_min = simple_laser
bc_x_max = open
bc_y_min = open
bc_y_max = open
bc_z_min = open
bc_z_max = open
end:boundaries
# y polarization
begin:laser
boundary = x_min
intensity_w_cm2 = I_focus
omega = las_omega
phase =-phasey + las_k * ((y-15 * micron)^2+z^2) / (2 * x_spot * (1 + (x_R / x_spot)^2 ) ) - gouy #sin(wt+phase)
profile = gauss(sqrt((y-20 * micron)^2+z^2), 0, w_bnd)
t_profile = gauss(time, t0_x, t0)
end:laser
# z polarization
begin:laser
boundary = x_min
intensity_w_cm2 = I_focus
omega = las_omega
pol_angle = pi/2
phase = -phasez+ las_k * ((y-15 * micron)^2+z^2) / (2 * x_spot * (1 + (x_R / x_spot)^2 ) ) - gouy #sin(wt+phase)
profile = gauss(sqrt((y-20 * micron)^2+z^2), 0, w_bnd)
t_profile = gauss(time, t0_x, t0)
end:laser
begin:species
name = electron
charge = -1.0
mass = 1.0
npart_per_cell = 16
number_density = if((x gt x_left) and (x lt x_right) and (y gt y_down) and (y lt y_up) and (z gt z_back) and (z lt z_front), n_plate, 0.0)
temp_ev =1
end:species
begin:species
name = ion
charge = 1.0
mass = 1836.0
npart_per_cell = 16
number_density = number_density(electron)
temp_ev =1
immobile = T
end:species
####output series####
#=============instantaneous fields =============
begin:output
#disabled = T
name = reflectedfield
file_prefix = reflect
dt_snapshot = 10* las_period
ex = always + single
ey = always + single
ez = always + single
end:output
Hi @kwang12008,
I don't run many reflection simulations myself, so I don't know if this is expected behaviour from EPOCH.
I do know that EPOCH's boundaries work best when lasers are injected perpendicular to the simulation edges. You could try rotating the system so that EPOCH's laser fires along the
Cheers,
Stuart
Hi @Status-Mirror, thanks for replying.
When I tilt the plasma plate 45 degrees, the laser is incident from the left boundary x=0 plane, and after reflection it propagates along y direction. In this case , the laser light is perpendicular to the boundary, but strange stray light still appear
Hi @kwang12008,
I don't think this is a bug in the code. While you may be starting with a target at temperature 1 eV, a PIC code will struggle to resolve this. You're likely seeing self heating, so the target will be much hotter by the time the laser reaches it.
The code will actually be simulating laser energy reflecting off a hot, dense plasma. Since the target particles have different energies, they respond differently in the laser field. You'll get a range of resulting currents, which all affect the laser propagation. I would expect what you see here - the laser is mostly reflected in the expected direction, with beams excited in other directions.
Hope this helps,
Stuart
Hi @Status-Mirror,
I tried to increase the grid to improve the resolution, and the light in other directions caused by self heating did decrease significantly.
Thanks a lot.
wang