PSF Analyzer

Description

Analyzing the PSF is done in a straight forward way: The residual phase of stored in each screen is transformed into a PSF by means of the well known

np.abs(fftForward(aperture*np.exp(1j*phase)))**2

aperture is represented by the telescope mirror defined in the setup file. A number of additional analyses is carried out in the resulting PSF, and the input phase.

  • the Strehl ratio is measured on the phase \(\phi\) as \(S = e^{-\sigma_\phi^2}\).
  • the Strehl ratio is measured on the PSF as \(S = I_{peak}/I_{ref, peak}\), where \(I\) is the PSF’s intensity distribution, and \(I_{ref}\) is the intensity distribution of a reference PSF resulting from a perfectly flat wavefront.
  • The tip and tilt excursion of the PSF is measured on the phase \(\phi\) by means of a least squares fit of a flat wavefront to the phase
  • The tip and tilt excursion of the PSF is measured on the PSF by means of fitting a 2D Gaussian to it.

Plot caption

When called on its own, or on a figure with sufficient available subplot space, frg_anaylzer.makeplot() will produce a figure like so:

../_images/psf.png

The caption for the figure could be:

Resulting time-averaged PSF in units of peak intensity. Additionally shown is the Strehl ratio derived from the peak intensity, denoted as “SR(PSF)”, and derived from the wavefront quality, denoted as “SR(WF)”. The tip-tilt statistics are shown in the lower part, also derived from the PSF directly as well as from the wavefronts. \(Q_{90}\) means that 90% of TT excursions are smaller than the quoted value.

Resulting properties

psf_analyzer exposes the following properties after psf_analyzer.finalize() has been called:

psf_analyzer properties
Property type Explanation
psf 2D ndarray (float) Time-averaged PSF.
strehl float Strehl ratio of PSF derived from peak intensity.
sr_wf float Strehl ratio of PSF derived from residual wave fronts.
ttx 1D ndarray (float) of length n_frames Global tip for each frame from Gauss-fitted PSF location (mas).
tty 1D ndarray (float) of length n_frames Global tilt for each frame from Gauss-fitted PSF location (mas).
ttilt 1D ndarray (float) of length n_frames Global excursion from centre, determined from wavefront (mas)
ttjit float rms of ttilt
ttq90 float 90% quantile of ttilt
ttjit_psf float rms of sqrt(`ttx`**2+`tty`**2)
ttq90_psf float 90% quantile of sqrt(`ttx`**2+`tty`**2)