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WCS Testing for BigBoss Optics

This document explains the principle and solution of WCS testing for BigBoss Optics, using wavefront sensors, defocused images, and compensation techniques. It also provides parameters and calculations for minimum defocus and pixel size.

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WCS Testing for BigBoss Optics

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  1. BigBoss Wavefront Sensor Ming Liang 8/25/2011

  2. P w P1 P2 F l l I2 I1 I0 f ΔZ ΔZ Principle of WCS Test the illuminations of defocused images on P1 and P2, and get the I1 and I2 in conjugate object space. Then apply equation (4) to get unknow wavefront of w If constrain W: the wavefront, the errors are in units of length. δc: a ring delta function around the edge.

  3. Solution of WCS • Calculate signal • Apply FFT and inverse FFT to solve the Poison equation as shown in the flow chart • Compensating the effect of the estimated aberrations get from the above solution, remapping the images either using Jacobian transformation or ray tracing. The residual aberrations are again estimated and compensated until the noise level is reached.

  4. BigBoss Optics

  5. BigBossWCS Parameters • The minimum defocus l should be: Where: r0: Fried parameter, which limites the resolution on entrance pupil. f : System focal length, for BigBoss f =16504 mm , λ : wavelength. l : Defocus r0 = 0.98 λ/ β

  6. BigBoss WCS Parameters Minimum defocus (mm) for BigBoss • Defocus: suppose the testing wavelength is at 0.6 μm, if the seeing β is chosen between 0.7” to 1” , the defocus l should be between about 5.6 to 1.8 mm. Currently, we chose 4mm . • Pixel size: the maximum pixel size should be • With the above given numbers and considering of sampling , chose the pixel size of 10 μm.

  7. Defocus And Sensitivity The drawing show sinuidal phase free space propagation from a 4 m aperture. The results show that the defocus will influence the space resolutions. Short defocus favorite for low frequency sensitivity, vice verse. • In the drawing: • Pupil aperture: 4 m • The space period of the sinusoid phases are 0.5 m and 1m respectively • In the 0.5m period testing, line 1 shows the optimal z, and line 2 shows the fringe half way shift. Using this will produce opposite signals. 2 1 Pupil position Space Period T = 1m Space Period T = 0.5m

  8. Separated Detectors • Wavefront sensor number and position: two or three wavefront sensors on the edge of the science focus. • Detector : two 2k x 2k ccds for intra and extra focal sensors respectively. Pixel size = 10 μm • Defocus: one detector is 4 mm in front of normal focus, the other is 4 mm behind. Intra focus wcs Wavefront sensors Extra focus wcs BigBoss Focus (3º FOV)

  9. Get Intra And Extra Images On BigBoss Normal focus Intra focus Extra focus Extra focus image I2 Intra focus image I1

  10. Piston Single Detector One 2k x 2k ccd move back and forth to get the intra and extra images. Wavefront sensors Intra focus wcs Extra focus wcs BigBoss Focus (3º FOV)

  11. Other Solutions • Shack Hartman • Phase diversity • Simplex algorithms • Donut

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