How to Correct Low Order Aberrations?

[AmitJha074]

Hi, I am pretty new to HCIPy so I would greatly appreciate any help. I'm sorry if this is not the right forum to ask for help.

• was generating an aberrated PSF and trying to correct some low-order aberrations like tip/tilt/ astigmatism etc.
• The results come out to be extremely weird, I'm not sure what is wrong. Any feedback is appreciated -
• The following is the code:

  
  from hcipy import *
  import numpy as np
  import matplotlib.pyplot as plt

Initialization

D_tel = 8 # Telescope diameter in meters wavelength = 1e-6 # Wavelength in meters

pupil_grid = make_pupil_grid(512, D_tel) aperture = circular_aperture(D_tel)(pupil_grid)

outer_scale = 20 # Outer scale of turbulence in meters velocity = 10 # Turbulence velocity in meters/sec Cn_squared = 1e-15 # Refractive index structure constant layer = InfiniteAtmosphericLayer(pupil_grid, Cn_squared, outer_scale, velocity)

Generate the turbulent wavefront

wf = Wavefront(aperture np.exp(2j np.pi pupil_grid.x 1), wavelength) turbulent_wf = layer(wf)

Convert wrapped phase to OPD

opd_aberrated = turbulent_wf.phase / (2 np.pi) wavelength

Display initial turbulent PSF

focal_grid = make_focal_grid(8, 16, reference_wavelength=wavelength, f_number=0.1) prop = FraunhoferPropagator(pupil_grid, focal_grid) img = prop(turbulent_wf) plt.figure() imshow_field(np.log10(img.intensity / img.intensity.max()), vmin=-3) plt.colorbar() plt.title("Original Aberrated PSF") plt.show()

Decompose the OPD into Zernike modes

zernike_basis = make_zernike_basis(4, D_tel, pupil_grid, starting_mode=1) # First four Zernike modes aperture_masked_opd = opd_aberrated * aperture # Apply mask to restrict within the aperture

Project onto the defocus mode (Zernike mode index 4 in Noll's ordering)

defocus_mode = zernike_basis[3] * aperture # Mode index 4 corresponds to defocus in this basis

Calculate projection of OPD onto the defocus mode

defocus_projection = np.dot(aperture_masked_opd, defocus_mode) / np.dot(defocus_mode, defocus_mode)

Remove the defocus term by subtracting it from the aberrated OPD

opd_corrected = aperture_masked_opd - defocus_projection * defocus_mode

Create the corrected wavefront with adjusted phase

phase_corrected = 2 np.pi opd_corrected / wavelength wf_corrected = Wavefront(aperture np.exp(1j phase_corrected), wavelength)

Display corrected PSF

corrected_img = prop(wf_corrected) plt.figure() imshow_field(np.log10(corrected_img.intensity / corrected_img.intensity.max()), vmin=-3) plt.colorbar() plt.title("Corrected PSF (Defocus Removed)") plt.show()

[ehpor]

I see that you closed this issue by yourself.

For reference, your problem was with the big tilt that you added. This makes the OPD itself wrap, which makes your projection of defocus on the wrapped OPD fail.

With tilt:

Without tilt:

# Display uncorrected and corrected OPD
corrected_img = prop(wf_corrected)
plt.figure()
plt.subplot(1,3,1)
plt.title('Original OPD')
imshow_field(aperture_masked_opd, cmap='RdBu')
plt.colorbar()
plt.subplot(1,3,2)
plt.title('Corrected OPD')
imshow_field(opd_corrected, cmap='RdBu')
plt.colorbar()
plt.subplot(1,3,3)
plt.title('Difference')
imshow_field(aperture_masked_opd - opd_corrected, cmap='RdBu')
plt.colorbar()
plt.show()