P2.7 SHARK-NIR system-level characterization at different telescope elevations

• Phase : 2
• Status : COMPLETE (only for Zenith)
• Category : Daytime testing (functionality and operability) (C3) + Daytime calibration (C4)
• Recurrence : once after instrument installation at telescope platform
• Duration : 4 days

Description

• SHARK-NIR system-level characterization and optimization as a function of the telescope elevation. Checking the pointing offset between SHARK-NIR and SOUL-AO. SOUL-AO tests. Measure the Non-Common Path Aberrations (NCPA). Note that for the Phase Diversity (PD) algorithm, we will apply the defocus with the ASM.

Prerequisites

• Use the Argos swing arm / RR mounted on the SX side. SHARK-NIR aligned to telescope.
• Phase-diversity algorithm is tested and working in simulation and using real images from the SCICAM (at Padova).

Procedure for pointing offset measurements and characterization

• Check the procedure for the NCPA. These measurements come as free with the NCPA measurements.

Procedure for SOUL-AO tests

• Check the procedure for the NCPA. These measurements come as free with the NCPA measurements.

Procedure for NCPA

• Start the tests with the telescope pointed to Zenith
  • Go to a specific derotation angle out of the five (every 45 degrees over 180 degrees full travel) we wanted to calibrate/estimate the NCPA.
    1. Using the Argos light source / RR light source, acquire the star at the SOUL WFS.
    2. Introduce one of the seeing conditions (0" or 0.5" or 0.8"). Close the AO loop.
    3. Check the PSF position at the SCICAM. Move the SOUL WFS stages to position the star of the SCICAM center. The stage positions should be the same (or very close) as the values after the alignment of SHARK-NIR to the telescope.
    4. For the AO loop closed that produces the best PSF at the pin of the pyramid of the SOUL WFS, save the ASM shape. Keep that shape steady on ASM.
    5. Perform the phase diversity algorithm by applying to the ALPAO DM the best shape for the SHARK-NIR PSF. The ASM introduces the defocus by moving the LGS WFS in the focal direction.
    6. Ideally, contrast is the metric to be used to find the best NCPA shape for the ALPAO DM. However, since the contrast is directly related to the PSF optical quality at the coronagraphic focal plane, which is the same (or very close to the same) at the scientific focal plane, we will use the SCICAM PSF images to determine the aberrations and, therefore to find the best shape to apply on the ALPAO DM.
    7. Only for Zenith angle, the following tests are also performed:
       • SOUL AO performances are estimated for various brightness of the on-axis source. If it is possible to tune the brightness only for SOUL WFS, that is done. If not, the source's brightness is reduced by introducing ND filters in front of the Ocean Optics (for example). SOUL WFS parameters (binning, number of modes corrected, etc.) are accordingly selected. SCICAM images are taken in every configuration to estimate the correction quality.
       • Instead of going for the best PSF at the pin of the pyramid of the SOUL WFS, we optimize the ASM shape to have the best optical quality at the SCICAM. This can be done by using the Trial & Error algorithm at the ASM and using images from SCICAM. Or, it can be done by converting the NCPA estimated using the PD algorithm and applying this at the ASM.
       • Checking the other two NCPA estimation techniques within SHARK-NIR (keeping the ASM shape having the same best flat as in point 4 above): Trial & Error algorithm and the use of Wollaston + DBI lens. Ideally, all three estimations should give the same results within error limits. Note that the Wollaston + DBI lens method has not produced good results using the SHARK-NIT internal sources. So, checking with the RR/Barillotto is important. Also, we anticipate half a day more for this activity.
  • Repeat all the steps above for the other seeing conditions.
  • Repeat the same steps (except point 7) for the other four derotation angles.
• Repeat the above steps for the other eight elevations of the telescope (zenith to 40deg zenithal distance in every 5deg step).
  • Note that point 3 above will provide the differential pointing offset measurements between SOUL and SHARK-NIR for the elevation derotation angle combination. This data will include the flexures of the RR as well, unfortunately.
  • All the SOUL AO close loops, especially the one for Zenith, will provide the SOUL AO performance estimates.

Templates

• SHARKNIR_cal_tec_NCPA_PD (Phase Diversity approach)
• SHARKNIR_cal_tec_NCPA_trial (Trial & Error approach)

Success criteria

• Measure the pointing offsets between SOUL and SHARK-NIR
• The SOUL-AO system is working in tandem with the SHARK-NIR system.
• Acceptable improvement of the on-axis PSF (Argos Swing arm calibration light source) while SOUL AO is closed with known disturbances.
• NCPA estimated and applied on the ALPAO-DM.
• Satisfactory PSF quality with closed-loop.
• The total residual after NCPA correction should be <30nm.

Notes

• See activity 8.1 in AD4 for more details.

LBTO support

• Authorize SHARK-NIR on the SX side.
• Permission to use the Argos Swing Arm.
• RR will be required on the SX side when not using the Argos swing arm and for different elevation angle tests.
• AO support.

Date performed and by whom

• November 11th, 12th, 13th, 14th by Luca, Daniele, Elena, Davide R./Fulvio

Results

• Due to technical issues, the NCPA verification was only performed at Zenith for different SHARK-NIR derotation angles. The results are good and consistent. More details can be found in the log. Here is the ​link.