Simulate Line-VISAR data

Building simulated data from a velocity profile.

Simple Example

target = Target(velocity_equation="step")
    
ray = Ray(pulse_length=10)
ray = target.reflect_off_target(ray)
    
etalon = Etalon(1, 1.5195)
etalon.set_VPF(2., lambda0=.532)
interferometer = Interferometer(etalon=etalon)
    
sweep = interferometer.output(ray, target)

plt.figure()
plt.imshow(sweep, aspect='auto', cmap="gray", extent=(0, 10, -2, 2))
plt.xlabel("Time [ns]")

Target class

The target class defines the velocity profile that will be recorded by the visar system (i.e. the shock front moving / interface velocity of a target of interest).

This velocity profile is loaded during the initialization of the target instance. Two built-in profiles are available for testing.

step : a discontinuous velocity jump
sigmoid : a sigmoid-shaped velocity jump
stationary : 0 velocity change, used in generating reference images

To help visualize the velocity profile, a helper plotting function is available, and can be called via the following command:

target.plot_velocity()

This generates two plots: a 3D plot of the velocity profile, and a 2D color plot. The 2D should be identical to what the "Visar analysis" script would return for the velocity map, if this simulated data were to be analyzed.

Loading a generic velocity profile

User-defined velocity profiles can be loaded. An example of how this is done is demonstrated in the functions

sin_step
spatial_var_step

In this case, a callable function is defined, which must except a time value, and a spatial location. If the user defined function requires more arguments, this can be simplified with use of a lambda function. e.g.

velocity_equation = lambda t, y : sin_step(20, .5, t, y, max_velocity=1)

the function is then loaded into the target during the initialization of the target instance.

target = Target(velocity_equation=velocity_equation)

Ray class

The ray instance defines the duration, as well as the spatial location over which the velocity profile will be recorded.

The values must be less than target._t and target._y, currently these are hard-coded into the Target.__init__, feel free to change them.

Etalon class

The etalon instance sets the VPF of the generated visar data, determined by twice the thickness (two passes through the etalon for a Mach-Zehnder interferometer) and the index of refraction:

etalon = Etalon(thickness=1, n=1.5195)

If you would like to explicitly set the VPF instead, this can be done with the helper function set_VPF, this then chanced the etalon thickness:

etalon.set_VPF(2, labda0=.532)

Similarly, this can be done with the etalon tau (temporal delay, in ns), set_tau

Interferometer class

The interferometer instance will carry out the mechanics of generating the fringe-comb pattern.

Initilization of the interferometer instance requires 2 arguments.

Interferometer(
    etalon,
    tau,
)

etalon An Etalon instance, used in determining the VPF of the generated data
tau the slit opening on the streak camera, this sets the temporal resolution.

Generation of the desired data is then accomplished by calling the output class method.

sweep = interferometer.output(ray, target, noise=False)

output excepts a Ray argument and a Target argument, and optional boolean argument to add noise to the generated data is also available; however, this method is still in development.

Reference Shot

A helper function is included to quickly generate a reference shot. This just generates the output from a stationary target.

reference_shot(
    save=False,
    noise=False
)

bdhammel / simulated-visar