BornAgain ≻ 24 ≻ Documentation ≻ Reference ≻ Simulation model ≻ Common settings ≻ Background

Poisson background

To add a Poisson background to a Simulation instance, use

bg = ba.PoissonBackground(seed=0)
simulation.setBackground(bg)

In this case, the output intensity is randomly distributed around the exact value with discrete Poisson statistics. The seed is a required argument: use a fixed value (e.g. seed=0) to reproduce the same noise realization, or a fresh one such as random.randrange(2**32) for an independent realization on each run.

The lower the intensity of the probing beam, the lower the signal-to-noise ratio.

Constant background

To add a constant background to a Simulation instance, use

bg = ba.ConstantBackground(1e3)
simulation.setBackground(bg)

Special cases

Specular simulation:

Background is applied before the reflectivity is normalized, so the background value will also be divided by the probe beam intensity.

Depth probe simulation:

Background is not supported.

Examples

Examples/specular/Background.py

Examples/scatter2d/Background.py

Scattering intensity

The script below shows how to add different types of background in the context of a GISAXS simulation of cylindrical particles on substrate.

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#!/usr/bin/env python3
"""
Cylinder form factor in DWBA with background/noise
"""
import random
import bornagain as ba
from bornagain import ba_plot as bp, deg, nm


def get_sample():
    """
    A dilute random assembly of cylinders on a substrate.
    """
    substrate_color = (0.28, 0.57, 0.82)
    substrate_mat = ba.RefractiveMaterial(
        "Substrate", substrate_color, 6e-6, 2e-8)
    particle_color = (0.86, 0.24, 0.18)
    particle_mat = ba.RefractiveMaterial(
        "Particle", particle_color, 6e-4, 2e-8)
    particle = ba.Particle(particle_mat, ba.Cylinder(5*nm, 5*nm))

    particle_layer = ba.Layer(ba.Vacuum())
    particle_layer.deposit2D(ba.Dilute2D(0.001, particle))
    substrate_layer = ba.Layer(substrate_mat)

    sample = ba.Sample()
    sample.addLayer(particle_layer)
    sample.addLayer(substrate_layer)
    return sample


def get_simulation(sample, background):
    beam = ba.Beam(1e8, 0.1*nm, 0.2*deg)
    n = 100
    detector = ba.SphericalDetector(n, 0., 2*deg, n, 0., 2*deg)
    simulation = ba.ScatteringSimulation(beam, sample, detector)
    simulation.setBackground(background)
    return simulation


def simulate(background, title):
    sample = get_sample()
    simulation = get_simulation(sample, background)
    result = simulation.simulate()
    result.setTitle(title)
    return result


if __name__ == '__main__':    
    # New seed each run; constant seed reproduces the same noise realization.
    poisson_seed = random.randrange(2**32)
    results = [
        simulate(ba.ConstantBackground(1e0), "Constant background"),
        simulate(ba.PoissonBackground(seed=poisson_seed), "Poisson noise"),
    ]    
    ba.showSample3D(get_sample(), sample_size=120*nm, seed=0)
    bp.plot2d_to_row(results, log_range=5, unit_aspect=1)
    bp.plt.show()
auto/Examples/scatter2d/Background.py