Issue with representing INSIGHT measurement using azimuthal modes

[msavagestfc]

I've been investigating how many azimuthal modes are needed to represent a realistic pulse for our laser system (using LASY 0.6.2) and have run into some strange behaviour. Using 'rt' geometry is working ok for describing simple (close to Gaussian) pulses but when I feed in a real INSIGHT measurement, even 100 modes isn't enough to get an accurate description of the pulse (compared to the laser object created using 'xyt' geometry - see below). There's also some odd oscillatory behaviour.

1 azimuthal mode:

2 azimuthal modes:

100 azimuthal modes:

'xyt' geometry

I also run into issues accurately representing a pulse defined entirely parametrically (Gaussian with zernike aberrations added) but I think this is mainly due to large zernike aberrations making a highly asymmetric pulse which is difficult to describe with FB modes (there is also no strange oscillatory behaviour in this case).

The relevant parts of my Python script are as follows:

laser_profile = FromInsightFile(insight_file, polarisation, omega0=wavelength)

lo = (0, -time_limit)
hi = (radial_limit, time_limit)

(radial limit and time limit are defined manually)

laser = Laser('rt', lo, hi, (500, 500), laser_profile, n_azimuthal_modes=100)

laser.show(show_intensity=True)
plt.show()

dimensions = 'xyt'
num_points = (300,300, 300)
lo = (-5beam_waist, -5beam_waist, -100e-15)
hi = (5beam_waist, 5beam_waist, 100e-15)

laser_xyt = Laser(dimensions, lo, hi, num_points, laser_profile)
laser_xyt.show(show_intensity=True)
plt.title('Laser pulse intensity')
plt.show()

[rob-shalloo]

Hi @msavagestfc , thanks for reporting this issue!

I guess the best people to investigate would be @hightower8083 or @MaxThevenet as they were involved in #229. Could one of you take a look?

Looking through the code, It could also be that the issue actually lies within FromArrayProfile, rather than the FromInsightFile profile itself, but I think one of the guys above will be better placed to judge.