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

• Phase : 2
• Status : Draft
• 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).

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. This measurements comes as free with the NCPA measurements.

Procedure for SOUL-AO tests

• Check the procedure for the NCPA. This measurements comes as free with the NCPA measurements.

Procedure for NCPA

• Start the tests with telescope pointed to Zenith
  • Go to a specific derotation angle out of the five we wanted to calibrate/estimate the NCPA.
    1. Using the Argos light source / RR light source, acquire the star at the SOUL WFS.
    2. Close the AO loop.
    3. Check the PSF position at the SCICAM. Move the SOUL WFS stages to position the star the SCICAM center. The stage positions should be same (or very close) to that the values after the alignemnt of SHARK-NIR to the telescope.
    4. For the AO loop closed that produce 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 diveristy algorithm with flat ALPAO DM. The focus is introduced by the ASM bymoving the LGS WFS in 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 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.
  • Repeat the same steps (except point 7) for the other four derotation angles.
• Repeat the above steps for the other 4 elevations of the telescope.

• Now, optimize the PSF shape on the SCICAM using the trial & error algorithm. The ALPAO-DM on the SHARK-NIR Bench is used to apply different modes. [Currently, this is the baseline approach].
• For the same elevation, keeping the same ASM shape as before and the same source, perform the phase-diversity test (with flat ALPAO-DM), using the Wollaston prism and dual-band imager lens configuration. Apply the obtained NCPA on the ALPAO DM within SHARK. Take SCICAM images to see the improvement. [In case the NCPA produced by the baseline approach is not stable enough for a longer period, and if more correction seems necessary for high contrast, we will be implementing this approach (for which we will be using the star itself as the source during nighttime)].
• Note that in the above two cases, the optical path contains the same optics (except for the Wollaston and DBI lens), including the dichroic and IN_TT of the deployable arm.
• Repeat these measurements for the decided discreet zenith angles (or elevation of the telescope) and SHARK-NIR DROT angle (fixed).

after ncpa_ zenith soul close loop on an aberrated PSF

Templates

• SHARKNIR_di_cal_NCPA (not released)

Success criteria

• Estimate the pointing offset and conclude if it is acceptable or not. If not acceptable, take proper actions to overcome this issue.
• 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