Profile from a file produced by lasy

class fbpic.lpa_utils.laser.FromLasyFileLaser(filename, t_start=0.0)[source]

Define a laser whose profile is determined by a lasy file.

When the laser is initialized by this function, FBPIC forces the beginning of the time axis in the lasy file to be zero (irrespective of the metadata for tmin that is actually present in the lasy file). This convention was chosen for convenience, because tmin in lasy could otherwise result in large delays before emitting the laser, especially when using lasy’s propagate feature.

Warning

This laser profile can only be emitted with the antenna method (not with the direct method).

Parameters:

  • filename (string) – The path to the lasy file.

  • t_start (float (in seconds), optional, default: 0) – Physical time (in the simulation), at which the laser will start being emitted. This can be used in order to introduce a time delay that was not originally present in the lasy file. (As explained above, FBPIC ignores any initial time offset in the lasy. This offset is replaced by t_start (or zero if unspecified).

Example

# Creating the lasy file
laser_profile = GaussianProfile(wavelength,polarization,
                        energy,spot_size,pulse_duration,t_peak=0)
dimensions     = 'rt'                              # Use cylindrical geometry
lo             = (0,-2.5*pulse_duration)           # Lower bounds of the simulation box
hi             = (5*spot_size,2.5*pulse_duration)  # Upper bounds of the simulation box
num_points     = (300,500)                         # Number of points in each dimension
laser = Laser(dimensions,lo,hi,num_points,laser_profile)
laser.propagate(-1e-3)  # Propagate backwards by 1 mm
laser.write_to_file('lasy_laser', 'h5')
# Note that, in the lasy file, tmin is now a large, negative number.
# (The peak of laser intensity still occurs 2.5*pulse_duration after tmin.)
# FBPIC ignores tmin when reading the file, and sets the start of
# the lasy time axis to zero instead. So, by default, the peak of
# the laser intensity would occur at `t= 2.5*pulse_duration` in FBPIC.
laser_profile = FromLasyFileLaser( 'lasy_laser_00000.h5', t_start=0.5*pulse_duration )
add_laser_pulse(sim, laser_profile, method='antenna', z0_antenna=0)
# Here, modify the `t_start`, which will result in the peak of intensity being
# emitted at `(2.5+0.5)*pulse_duration` instead of `2.5*pulse_duration`.
# Since the `z0_antenna` was set to `0` here, this is as if the centroid
# of the laser would have been initialized at `z = -3*c*pulse_duration` at `t=0`
# (with then ``direct`` method).