Lyot Stop Focal Plane Mask OAP3 Out of plane spherical mirror

Moving the Focal Plane (coronagraphic) Mask to correct pupil motion, misaligns the cal-interferometer Focal plane mask If the focal plane mask pivots about the focus of OAP 3, the interferometer is not misaligned. But if the tip/tilt mount is not exactly at the focus, there will both be an OPD change and also a tip/tilt change when the focal mask is rotated. OAP 3 Amount of misalignment if pivot is 1mm off OAP 3 focus and pupil motion is 1mm. 1mm (500mm fl?) => ~0.002 radian motion. That potentially causes an opd change of 0.002*1mm~2um and a tilt change of 2um/0.5m ~4 urad.

What is the size of dispersion (that the ADC is supposed to remove) Atmos dispersion 1 st order is due to the wedge of air on top of the telescope. The wedge causes atmos Refraction (n-1)*wedge angle (where n is index of air ~1+3x10-4 Dispersion between 2 different is (n( 1 )-n( 2 ))*wedge angle Dispersion is ~46 mas (30deg zenith) between 1.2um and 1.7um But the IFU splits this into ~23? spectral bands. Within 1 spectral bin ~20nm wide the dispersion is ~ 2mas. (vs l/D of 68 mas) Since the LOCI folks always recenter the image at every spectral band, the gross dispersion between 1.2um and 1.7um doesn’t really matter. If the ADC is turned off, there will be almost zero impact on science if LOCI is used remove static speckles. During engineering run, we’ll turn the ADCs off. We request this also happen during scienc run, if the problem is not fixed by realignment of ADC.

Fixing the ADC Aligning the ADC so there is no pupil motion. – Even though the ADC is not at a pupil, it is possible to design an ADC that has zero pupil motion when the prisms are rotated. – Two effects cause pupil motion, one intrinsic to the ADC prism design, the other due to alignment. It is possible to cancel the ADC prism motion with proper alignment. (C. Shelton wrote up an alignment procedure for his ADC design) Normally use two prisms If each prism alone, has a small angular deviation, rotation of the prism causes pupil motion (in a circle). Tilt of the rotation axis of the prism does the same thing. The 2 nd can be used to nullout the 1 st.

Tip/Tilt Sensor Long term – InGaAs quad cell, NEP = 2x w/rthz (2mm quad cell) SNR~ 1 in 1 sec when input flux is 2x w 2x w ~ 1.4x10 5 photons/s – The Hawaii chip in the cal-system has ~20e read noise (no dark compared to the 300K) 64*64 pixels are used in a mode that has a SNR hit of ~7X over use as a quad cell. SNR = 1 at 4x10 3 photons/s. – Tip/tilt sensitivity ~ 4 mag more sensitive than the quad cell, to 10~11 mag. Mid term - Dichroic beam splitter – ~80% of total photons to Quad cell +0.25mag. ~80% of 1.65um photons to Cal- system. Immediate future (March run) – If we can buy it in time 30/70 or 20/80 beam splitter (70% to quad cell) 0.4 mag less sensitivity. – We know we can buy a 50/50 BS (0.75 mag sensitivity loss)

Lyot Stop Location Long term. The cal system needs the lyot stop in the arm that goes to the IFU, but not in the arm that goes to the HOWFS camera – Should JPL start a redesign effort, should AMNH start such an effort, (in april) March run – Will remove lyot stop for engineering night. Replace for science nights. – Engineering tests In lab, measure wavefront immediately in front of coronagraphic mask. 150~200nm rms causing 1% speckles in the square pattern. Perhaps another 200nm of low order (astig, coma etc.) – Zernike tuning of AO wavefront affects low order zernikes, light that goes down the 5.2 /D hole. But very little change in 5~15 /D speckles – Attempt to feed back to AO system to reduce the mid-freq wavefront errors. (replacement for MGS) – 5~10X reduction if we are slightly lucky. (hope for 100x reduction in the lab) On telescope measurement of mid-spatial freq errors (is it diff from the lab), – measure WFE vs hour angle and dec. (flexure dependent WF bias) – Measure WFE vs time (at fixed telescope pointing, temp dependence?) On star measurements (quantitative measurement of wavefront vs time) Analyze data for july run. (If we measure WFE vs HA, DEC is it possible to generate a series of tables for the AO system? (every 15 deg in HA or Dec, upload a different WFE table for the AO WFS?) – Limit to speckle reduction, non-deterministic behavior of P241 WFS and time/flexure variability.

Support from Coronagraph/IFU Team (testing support) We’d like to articulate the Tip/tilt mirror in a known way. – Ideally to lambda/(20D). In 4mm beam, this means 20urad, or about 4 arcsec. Can we command the tip/tilt mirror with 4 arcsec repeatability? – We also need to know “how” to command the tip/tilt mirror. M. Troy has already told us that the TT mirror for the AO system is not sufficiently accurate to calibrate the S curve on the AO WFS. The Cal-system integration and much of its testing should be done when the IFU is brought back up. We’d like to see the quality of the images at the IFU (brightness of square speckle pattern). After we’ve given the AO system a new set of (static) offsets after using the cal-system to measure the wavefront error.