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LaserModulator Class

The LaserModulator class is a subclass of PhysProc that simulates the energy modulation of a particle beam in an undulator. It provides methods to calculate laser wavelength, undulator transport matrix element begin:math:textbegin:math:text R_56 end:math:textend:math:text, and apply laser modulation to the beam.

Class Definition​

class LaserModulator(PhysProc):
    def __init__(self, step=1):
        """
        Initialize the LaserModulator with default parameters or user-defined values.

        Parameters
        ----------
        step : int, optional
            Step size used by the PhysProc base class, default is 1.
        """

Parameters​

  • step (int): The step size used by the PhysProc base class (default is 1).

Attributes​

  • dE (float): Amplitude of the energy modulation on-axis in [GeV] (default is 12500e-9).
  • Ku (float): The undulator parameter (default is 1.294).
  • Lu (float): The undulator length in meters (default is 0.8).
  • lperiod (float): The undulator period length in meters (default is 0.074).
  • sigma_l (float): The laser pulse length (longitudinal Gaussian sigma) in meters (default is 300e-6).
  • sigma_x (float): The transverse beam size in the x-direction in meters (default is equal to sigma_l).
  • sigma_y (float): The transverse beam size in the y-direction in meters (default is equal to sigma_l).
  • x_mean (float): The transverse beam offset in the x-direction in meters (default is 0).
  • y_mean (float): The transverse beam offset in the y-direction in meters (default is 0).
  • z_waist (float or None): The shift of the laser waist position in meters. If None, a simple Gaussian beam model is used.
  • include_r56 (bool): Flag to include the R56 effect in the modulation. Default is False.
  • laser_peak_pos (float): The offset of the laser peak position relative to the mean of the particle array's tau values. Default is 0.

Methods​

lambda_ph(self, energy)​

Calculate the wavelength of the laser pulse.

Parameters​

  • energy (float): The beam energy in [GeV].

Returns​

  • float: The laser wavelength in [m].

Notes​

This method computes the laser wavelength based on the undulator period (lperiod), the undulator parameter (Ku), and the beam's gamma factor (calculated from the given energy).

r56(self, energy)​

Calculate the R56R_{56} for the undulator.

Parameters​

  • energy (float): The beam energy in [GeV].

Returns​

  • float: The value of R56R_{56} in [m].

Notes​

This method computes the dispersion-like term introduced by the undulator, dependent on the beam's Lorentz factor (gamma) and undulator parameter (Ku).

apply(self, p_array, dz)​

Apply the laser modulation to the particle array over a distance dz.

Parameters​

  • p_array (ParticleArray): The particle array object containing phase space variables.
  • dz (float): The integration step length for applying the modulation.

Returns​

  • None

Notes​

  • Verifies the effective undulator length L and checks if it matches the undulator length Lu. If the lengths do not match, a warning is issued.
  • Calculates the laser wavelength lambda_ph and wave number k_ph.
  • Computes the energy modulation amplitude A and applies the modulation based on transverse offsets (x, y), longitudinal offset (tau), and a Gaussian profile.
  • If include_r56 is True, the R56R_{56} effect is included.
  • If a laser waist shift (z_waist) is provided, a more complex model with curvature is used for the modulation.