P3K WFS development meeting #2 V Velur Caltech Optical Observatories Pasadena, CA

Agenda TTFA vs. TT+ slow WFS approach. Sky coverage calculations for the new approach. Details of the new scheme Pyramid WFS articles Progress on Ventura retreat action items

Comparison of different sensors for P3K Assuming that we have a 0.25” field stop and m v = 20 TT guide star

Detector specifications and digital field stop Hawaii 2RG -18 m pixels, 32 read out amps w/ rapid guiding mode for TT sensing. If we choose a plate scale of 0.25”/pixel we could use 100x100 pixels for acquisition and 2x2 (QC) for guiding. QC sensing will be done in RG mode using one dedicated amplifier. Lots of real estate to facilitate both the TT sensor and a 6x6 IR WFS on the same chip The 6x6 IR WFS (henceforth called IRMOWFS) will be able to work as a regular (NGS) WFS or act as a slow WFS using 25% (or 10%) of the light from the TT path.

Schematic layout

Noise vs. (Fowler) sample example plot

IRMOWFS part of detector

IRMOWFS read out rate estimate For this configuration with 4 amplifiers:  Pixel read out rate = 10  sec,  line skip = 2  sec,  pixel skip = 2  sec,  frame read time = 20  sec.  1 frame takes = 10*10-6 * 36 (active pixels) (pixel skips) *2*10-6 = 760  sec.  with the frame overhead we hit a ceiling at 1282 Hz.  We also have to reset, read a backgnd image and read out again. So there is an additional over head of about 2-3! Which brings the frame rate to 640 Hz.  If we want to Fowler sample to beat down the noise by 8 frames we run at 64 fps!  The TT sensor will be read out over a separate 5 MHz/pixel amplifier (noise characterization still to be done).

Another way of using the chip

Read out rate estimate. For this configuration with 2 amplifiers:  Pixel read out rate = 10  sec,  line skip = 2  sec,  pixel skip = 2  sec,  frame read time = 20msec.  1 frame takes = 10*10-6 * 72 (active pixels) + 16 (pixel skips) *2*10-6 = 750  sec.  with the frame overhead we hit a ceiling at 1298 Hz.  We also have to reset, read a backgnd image and read out again. So there is an additional over head of about 2-3! Which brings the frame rate to 649 Hz.  If we want to Fowler sample to beat down the noise by 8-10 frames we run at fps (4 electrons to 10 electrons of noise)  The TT sensor will be read out over a separate 5 MHz/pixel amplifier (noise characterization still to be done).  There may be a possibility of making the pixel read time 5  sec without much overhead.

Pyramid sensor references: 1.R.Ragazzoni, "Pupil plane wavefront sensing with an oscillating prism," J. Mod. Opt. 43, (1996). 2.C. Verinaud, "On the nature of the measurements provided by a pyramid wave-front sensor," Opt. Commun.233, (2004). 3.J. B.Costa et. al., "Is there need of any modulation in the pyramid wavefront sensor," in Adaptive Optical System Technologies II, P. L.Wizinowich and D. Bonaccini, eds., Proc. SPIE 4839, (2003). 4.Brian Bauman, "Optical design for extremely large telescope adaptive optics systems" PhD thesis, U. Arizona. (available from LAO’s website).