P2.6 Measurement of NCPA

• Phase : 2
• Status : Draft
• Category : Daytime testing (functionality and operability) (C3) + Daytime calibration (C4)
• Recurrence : after instrument installation at telescope platform
• Duration : 8 days

Description

• Measure the Non-Common Path Aberrations (NCPA).

Prerequisites

• Use of 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

• Go to a specific elevation of the telescope.
• Close the AO loop for the on-axis light source to produce the best PSF at the pin of the pyramid of the SOUL WFS. Keep that shape steady on ASM.
• 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) making use of 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/or 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).

Success criteria

• 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.
• When not using the Argos swing arm and for different elevation angle tests, RR will be required on the SX side.
• AO support.

Associated SHARK-NIR personnel

Date performed and by whom

Comments

• add dynamic disturbance at ASM for 0.7", 1", 1.5" - looks t open loop and closed loop strehl. then closed loop + TT strehl, then closed loop + TT + NCPA corrected strehl.