Using Laser pulses

Introduction

Users may optionally define an arbitrary number of laser pulses to be added to the simulation. Each laser pulse is added through a call to the sim_add_laser() routine:

void sim_add_laser( t_simulation* sim, t_emf_laser* laser)

This routine should be called inside sim_init(), somewhere after the call to sim_new(), e.g.:

void sim_init( t_simulation* sim ){

  //...
  // Initialize Simulation data
  sim_new( sim, nx, box, dt, tmax, ndump, species, n_species );

  // Add laser pulse (this must come after sim_new)
  t_emf_laser laser = {
    .start = 17.0,
    .fwhm  = 2.0,
    .a0 = 2.0,
    .omega0 = 10.0,
    .polarization = M_PI_2
    };
  sim_add_laser( sim, &laser );

  // ...
}

Laser pulse parameters - 1D

Laser pulse parameters are specified by a t_emf_laser variable supplied to the sim_add_laser() function. In 1D the t_emf_laser structure has the following fields:

Laser parameters	Description
type	PLANE for a plane wave or GAUSSIAN for a gaussian beam
start	Front edge of the laser pulse
fwhm	FWHM of the laser pulse duration
rise, flat, fall	Rise / flat / fall time of the laser pulse
a0	Normalized peak vector potential of the pulse
omega0	Laser frequency
polarization	Laser polarization angle, 0 aligns $E$ field along $x_2$
W0	Gaussian beam waist
focus	Focal plane position
axis	Position of the optical axis

All parameters are in normalized simulation units except for the normalized peak vector potential, $a_0$, which is adimensional.

Using the fwhm parameter will override the rise, flat and fall parameters. Specifically, it sets rise = fwhm/2, flat = 0, and fall = fwhm/2.

The following example launches a laser starting at position 17.0, with a (temporal) full width at half max of 2.0. The peak normalized vector potential is 2.0, and the laser frequency is 10.0. The polarization degree is $\pi/2$, which aligns the $E$ field along the $x_3$ direction. All values are in normalized simulation units.

t_emf_laser laser = {
  .start = 17.0,
  .fwhm  = 2.0,
  .a0 = 2.0,
  .omega0 = 10.0,
  .polarization = M_PI_2
};
sim_add_laser( sim, &laser );

Laser pulse parameters - 2D

In 2D ZPIC also supports Gaussian beam laser pulses (besides plane wave pulses). The t_emf_laser structure has the additional fields:

Laser parameters	Description
type	PLANE (default) for a plane wave or GAUSSIAN for a gaussian beam
W0	Gaussian beam waist
focus	Focal plane position
axis	Position of the optical axis

All parameters are in normalized simulation units. The following is a 2D example of a gaussian laser pulse. It uses the same parameters as the previous example, set the beam focus waist to $W_0=4.0$, the focal plane position to $x=20.0$, and the propagation axis to $y=12.8$.

t_emf_laser laser = {
  .type = GAUSSIAN,
  .start = 17.0,
  .fwhm  = 2.0,
  .a0 = 2.0,
  .omega0 = 10.0,
  .W0 = 4.0,
  .focus = 20.0,
  .axis = 12.8,
  .polarization = M_PI_2
};
sim_add_laser( sim, &laser );