def get_current(self,
t=None,
iteration=None,
species=None,
select=None,
bins=100,
plot=False,
**kw):
"""
Calculate the electric current along the z-axis for selected particles.
Parameters
----------
t : float (in seconds), optional
Time at which to obtain the data (if this does not correspond to
an available file, the last file before `t` will be used)
Either `t` or `iteration` should be given by the user
iteration : int
The iteration at which to obtain the data
Either `t` or `iteration` should be given by the user
species : string
Particle species to use for calculations
select : dict, optional
Either None or a dictionary of rules
to select the particles, of the form
'x' : [-4., 10.] (Particles having x between -4 and 10 meters)
'z' : [0, 100] (Particles having z between 0 and 100 meters)
bins : int, optional
Number of bins along the z-axis in which to calculate the current
plot : bool, optional
Whether to plot the requested quantity
**kw : dict, otional
Additional options to be passed to matplotlib's `plot` method
Returns
-------
A tuple of arrays containig
- The current in each bin in Ampere
- A FieldMetaInformation object
(see object's docstring for more details)
"""
# Get particle data
z, uz, uy, ux, w, q = self.get_particle(
var_list=['z', 'uz', 'uy', 'ux', 'w', 'charge'],
t=t,
iteration=iteration,
species=species,
select=select)
# Length to be seperated in bins
if w.size > 0:
min_z = np.min(z)
len_z = np.max(z) - min_z
# Calculate Lorentz factor for all particles
gamma = np.sqrt(1 + ux**2 + uy**2 + uz**2)
# Calculate particle velocities
vz = uz / gamma * const.c
# Length to be seperated in bins
len_z = np.max(z) - np.min(z)
vzq_sum, _ = np.histogram(z, bins=bins, weights=(vz * w * q))
# Calculate the current in each bin
current = np.abs(vzq_sum * bins / (len_z))
else:
current = np.zeros(bins)
len_z = 0
min_z = 0
# Info object with central position of the bins
info = FieldMetaInformation({0: 'z'},
current.shape,
grid_spacing=(len_z / bins, ),
grid_unitSI=1,
global_offset=(min_z + len_z / bins / 2, ),
position=(0, ))
# Plot the result if needed
if plot:
check_matplotlib()
iteration = self.iterations[self._current_i]
time_s = self.t[self._current_i]
plt.plot(info.z, current, **kw)
plt.title("Current at %.2e s (iteration %d)" %
(time_s, iteration),
fontsize=self.plotter.fontsize)
plt.xlabel('$z \;(m)$', fontsize=self.plotter.fontsize)
plt.ylabel('$I \;(A)$', fontsize=self.plotter.fontsize)
# Return the current and bin centers
return (current, info)
def get_spectrum(self,
t=None,
iteration=None,
pol=None,
m='all',
plot=False,
**kw):
"""
Return the spectrum of the laser
(Absolute value of the Fourier transform of the fields.)
Parameters
----------
t : float (in seconds), optional
Time at which to obtain the data (if this does not correspond to
an available file, the last file before `t` will be used)
Either `t` or `iteration` should be given by the user.
iteration : int
The iteration at which to obtain the data
Either `t` or `iteration` should be given by the user.
pol : string
Polarization of the field. Options are 'x', 'y'
m : int or str, optional
Only used for thetaMode geometry
Either 'all' (for the sum of all the modes)
or an integer (for the selection of a particular mode)
plot: bool, optional
Whether to plot the data
**kw : dict, otional
Additional options to be passed to matplotlib's `plot` method
Returns
-------
A tuple with:
- The 1D spectrum on axis
- A FieldMetaInformation object
"""
# Check if polarization has been entered
if pol not in ['x', 'y']:
raise ValueError('The `pol` argument is missing or erroneous.')
# Get a lineout along the 'z' axis,
slice_across = self._get_slicing_for_longitudinal_lineout()
# Get field data
field1d, info = self.get_field(t=t,
iteration=iteration,
field='E',
coord=pol,
m=m,
slice_across=slice_across)
# FFT of 1d data
dt = (info.z[1] - info.z[0]) / const.c # Integration step for the FFT
fft_field = np.fft.fft(field1d) * dt
# Take half of the data (positive frequencies only)
spectrum = abs(fft_field[:int(len(fft_field) / 2)])
# Create a FieldMetaInformation object
T = (info.zmax - info.zmin) / const.c
spect_info = FieldMetaInformation({0: 'omega'},
spectrum.shape,
grid_spacing=(2 * np.pi / T, ),
grid_unitSI=1,
global_offset=(0, ),
position=(0, ))
# Plot the field if required
if plot:
check_matplotlib()
iteration = self.iterations[self._current_i]
time_s = self.t[self._current_i]
plt.plot(spect_info.omega, spectrum, **kw)
plt.xlabel('$\omega \; (rad.s^{-1})$',
fontsize=self.plotter.fontsize)
plt.ylabel('Spectrum', fontsize=self.plotter.fontsize)
plt.title("Spectrum at %.2e s (iteration %d)" %
(time_s, iteration),
fontsize=self.plotter.fontsize)
return (spectrum, spect_info)
def get_spectrogram(self,
t=None,
iteration=None,
pol=None,
plot=False,
**kw):
"""
Calculates the spectrogram of a laserpulse, by the FROG method.
Mathematically:
$$ s(\omega, \tau) = | \int_{-\infty}^{\infty} E(t) |E(t-\tau)|^2
\exp( -i\omega t) dt |^2 $$
See Trebino, R: Frequency Resolved Optical Gating: The measurements of
Ultrashort Laser Pulses: year 2000: formula 5.2
The time is centered around the laser pulse.
Parameters
----------
t : float (in seconds), optional
Time at which to obtain the data (if this does not correspond to
an available file, the last file before `t` will be used)
Either `t` or `iteration` should be given by the user.
iteration : int
The iteration at which to obtain the data
Either `t` or `iteration` should be given by the user.
pol : string
Polarization of the laser field. Options are 'x', 'y'
plot: bool, optional
Whether to plot the spectrogram
**kw : dict, otional
Additional options to be passed to matplotlib's `imshow` method
Returns
-------
- A 2d array with spectrogram
- info : a FieldMetaInformation object
(see the corresponding docstring)
"""
# Get a lineout along the 'z' axis
slice_across = self._get_slicing_for_longitudinal_lineout()
# Get the field envelope
env, _ = self.get_laser_envelope(t=t,
iteration=iteration,
pol=pol,
slice_across=slice_across)
# Get the field
E, info = self.get_field(t=t,
iteration=iteration,
field='E',
coord=pol,
slice_across=slice_across)
Nz = len(E)
# Get time domain of the data
tmin = info.zmin / const.c
tmax = info.zmax / const.c
T = tmax - tmin
dt = T / Nz
# Normalize the Envelope
env /= np.sqrt(np.trapz(env**2, dx=dt))
# Allocate array for the gating function and the spectrogran
E_shift = np.zeros_like(E)
spectrogram = np.zeros((2 * Nz, Nz))
# Loop over the time variable of the spectrogram
for i in range(Nz * 2):
itau = i % Nz
# Shift the E field and fill the rest with zeros
if i < Nz:
E_shift[:itau] = env[Nz - itau:Nz]
E_shift[itau:] = 0
else:
E_shift[itau:] = env[:Nz - itau]
E_shift[:itau] = 0
EE = E * E_shift**2
fft_EE = np.fft.fft(EE)
spectrogram[i, :] = np.abs(fft_EE)**2
# Rotate and flip array to have input form of imshow
spectrogram = np.flipud(np.rot90(spectrogram[:, int(Nz / 2):]))
# Find the time at which the wigner transform is the highest
maxi, maxj = np.unravel_index(spectrogram.argmax(), spectrogram.shape)
tmin = -(T - T / spectrogram.shape[1] * maxj)
info = FieldMetaInformation({
0: 'omega',
1: 't'
},
spectrogram.shape,
grid_spacing=(2 * np.pi / T, dt / 2.),
grid_unitSI=1,
global_offset=(0, tmin),
position=(0, 0))
# Plot the result if needed
if plot:
check_matplotlib()
iteration = self.iterations[self._current_i]
time_s = self.t[self._current_i]
plt.imshow(spectrogram,
extent=info.imshow_extent,
aspect='auto',
**kw)
plt.title("Spectrogram at %.2e s (iteration %d)" %
(time_s, iteration),
fontsize=self.plotter.fontsize)
plt.xlabel('$t \;(s)$', fontsize=self.plotter.fontsize)
plt.ylabel('$\omega \;(rad.s^{-1})$',
fontsize=self.plotter.fontsize)
return (spectrogram, info)