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P3K WFS development meeting #2. V Velur Caltech Optical Observatories Pasadena, CA 91125. 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.
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P3K WFS development meeting #2 V Velur Caltech Optical Observatories Pasadena, CA 91125.
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 mv = 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.
IRMOWFS read out rate estimate For this configuration with 4 amplifiers: • Pixel read out rate = 10sec, • line skip = 2sec, • pixel skip = 2sec, • frame read time = 20sec. • 1 frame takes = 10*10-6 * 36 (active pixels) + 134 (pixel skips) *2*10-6 = 760sec. • 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).
Read out rate estimate. For this configuration with 2 amplifiers: • Pixel read out rate = 10sec, • line skip = 2sec, • pixel skip = 2sec, • frame read time = 20msec. • 1 frame takes = 10*10-6 * 72 (active pixels) + 16 (pixel skips) *2*10-6 = 750sec. • 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 60-80 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 5sec without much overhead.
Pyramid sensor references: • R.Ragazzoni, "Pupil plane wavefront sensing with an oscillating prism," J. Mod. Opt. 43, 289-293 (1996). • C. Verinaud, "On the nature of the measurements provided by a pyramid wave-front sensor," Opt. Commun.233, (2004). • 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, 288-298 (2003). • Brian Bauman, "Optical design for extremely large telescope adaptive optics systems" PhD thesis, U. Arizona. (available from LAO’s website).