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HOWFS Design Update 2/27/08

HOWFS Design Update 2/27/08. C. Baranec Pasadena, CA February 27 th 2008. Conceptual design Diffraction effects Other issues Conclusions / Future work. Conceptual Design 1. Decided on system of exchanging lenslet arrays. Reimaging lens. OAP2 f ocus. Collimation lens. Lenslet

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HOWFS Design Update 2/27/08

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  1. HOWFS Design Update 2/27/08 C. Baranec Pasadena, CA February 27th 2008

  2. Conceptual design • Diffraction effects • Other issues • Conclusions / Future work

  3. Conceptual Design 1 • Decided on system of exchanging lenslet arrays Reimaging lens OAP2 focus Collimation lens Lenslet array CCD Swap out lenslet arrays. Each has the same pupil diameter, but different focal lengths.

  4. Conceptual Design 2 • Identified plate scales at different sampling modes (x64, x32, x16, x8)

  5. Diffraction effects • Required lenslet arrays for x64 and x32 sampling, low Fresnel number (FN<1), lower than any other operating or planned AO system • Issue with ‘focal length’ in low FN resolved • Currently simulating impact of crosstalk (finishing in next two weeks) • Have setup lab experiment to verify simulations of intensity distribution behind lenslet arrays

  6. Simulation and Reality P3K 616nm FN=0.66 Lab exp 808nm FN~0.69

  7. Crosstalk effects • Insert movie here

  8. Center of Mass (COM) response P3K x64 • Transfer curve for the tilted central subaperture • Plate scale: 1 pix = 2.1” • Subaperture size: 2x2 pixels

  9. Crosstalk on adjacent slopes Crosstalk: a ~10-14% effect on adjacent slopes for P3K x64 Estimating up to an additional 10% in RMS WFE

  10. Other issues • CCD characterization – namely dark current and its affect on binning chip to get desired plate scales, especially in x8 mode where we will be using faint NGS • Refined optical design – currently paraxial • Design relay • Collimation lens • Lenslet arrays – quotes from MEMSoptical, Wavefront sciences, Vitrum

  11. Conclusions / Future work • Continuing characterization of crosstalk in simulation • Exactamount of additional reconstruction error? • Mitigation strategies (short-pass filter, less subapertures) • Finalization of optical system design • Schedule – preliminary optical design by mid-April • Obtaining SURF student to help assemble/align/characterize system during the summer. • Poster on P3K WFS for SPIE

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