a Programmable Spatial Light Modulator Presented at Mirror - PowerPoint PPT Presentation

Enhanced Interferometry with a Programmable Spatial Light Modulator Presented at Mirror Technology SBIR/STTR Workshop June 7 th to 9 th , 2010 Millennium Hotel, Boulder CO by James D. Trolinger and Joshua S. Jo MetroLaser, Inc. jtrolinger@metrolaserinc.com This work was supported by NASA Goddard Space Flight Center under SBIR Phase II contract #NNX08CA25C (POC’s: Geraldine Wright and David Content) This presentation is approved for General Public release 1

MetroLaser Irvine, California Presentation Summary  Summarize the problem & innovation  Describe the hardware and software ◦ Digital Interferometry with preconditioned wavefronts ◦ Hybrid Hartmann/Digital Interferometry  Typical measurements  Potential Applications  Future Work 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Irvine, California The Problem Being Addressed Modern optical components such as aspheres are difficult to inspect. Interferometry, the usual solution, lacks the required dynamic range. Too many fringes are produced. Adapting interferometry for null measurements currently necessitates special optical components for each inspected component. 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Irvine, California Innovation/Solution  Incorporate a programmable SLM into an optical inspection instrument enabling: ◦ Combined interferometry and Hartmann Sensing ◦ Virtually unlimited dynamic range ◦ Extended dynamic range of interferometry by preconditioning waves ◦ Null testing on almost any component using off the shelf optics.  Incorporate Instantaneous Digital Interferometry Technology 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Irvine, California Challenges Faced and Solved  Incorporating the SLM into a PhaseCam  Integrating Hartmann and Digital Interferometry  Calibrating the SLM - Phase-only mode by controlling polarization - Corrected gamma curve, i.e. linear phase shift versus grayscale value  Impressing the required phase function on the SLM  Identifying and minimizing errors and noise 6-7-2010-Monday Jtrolinger@metrolaserinc.com

Conventional Shack-Hartmann Characteristics CCD array Wavefront being  Lenslet diameters, d, define measured spatial resolution over the wavefront being measured. (sensitivity) proportional  to ƒ, which should be less than d to prevent confusion Lenslet Without aberration With aberration d f f tan ‘ Measuring aberration of the eye with wavefront technology ’ Simulated by Zemax Giuseppe Colicchi, et al Zur Veröffentlichung eingereicht bei “Physics Education”, 2006 6 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Key Components: SLM, Pixelcam* Irvine, California Pixelated Phasecam for a detector SLM for a compensator • Spatial phase shifting interferometer  Programmable holographic • Single shot, insensitive to vibration optical element Reference  Produce wavefronts of any RCP shape and can simulate Polarization Polarization freeform optical surfaces LCP Interferometer Interferometer object beam  Holoeye SLM Detector ◦ SLM can produce a phase Mask (micropolarizer) up to 2 π at 632.8nm ◦ Assign 0 to 255 grayscale values to 0 to 2 π (or 1 λ ) Phase information of the object, ∆Ф (x,y) can be obtained from the ◦ Can generate higher 4 intensities on each unit cell. 90 0 phases by wrapping phase 270 180 ◦ Can provide more than *Produced and Trademark by 4D Technologies, 150 wave tilt Inc, Tucson, AZ http://www.4dtechnology.com ◦ Pixel size ~ 19 microns. ◦ 19.5 x 14.6mm size 7 (1024 x768 pixels) 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Hybrid Hartmann & Digital Interferometer Irvine, California Optics Under Inspection λ /2 λ /4 SLM polarizer λ /2 BS PBS λ /4 SLM preconditions the test λ /2 LCP RCP wavefront Cam Pixelated Laser 6-7-2010-Monday Jtrolinger@metrolaserinc.com 8

MetroLaser Using a SLM as a Scanning Shack-Hartmann Component Irvine, California Optics Under Inspection λ /4 SLM PBS BS s V ≠ 0 λ /2 on SLM • SLM preconditions the test wavefront • SLM selects a pencil of light from the Cam Pixelated wavefront and directs it to the test object and focuses it on the CCD Laser • Any deviations on CCD will characterize the quality of the test object. 6-7-2010-Monday Jtrolinger@metrolaserinc.com 9

Scanning Shack-Hartmann System Data Screen Control Screen Control screen is a map of a scanned aperture (or pencils light) of the SLM. No Overlap of Focused Spot Programmable Aperture Size Analyzer Polarizer Expanded Laser Beam CCD Lens Sensor Test SLM Object

Scanning Shack-Hartmann System Data Screen Control Screen ‘ Pencils’ of light are deflected by the test object’s slope of wavefront as they scan the object. SLM corrects Aberrations Analyzer Polarizer Expanded Laser Beam CCD Lens Sensor Test SLM Object

Scanning Shack-Hartmann System Data Screen Control Screen Data screen maps, in time, the sequence of angular deviations caused by the object. Dynamic range is limited only by the CCD size. Analyzer Polarizer Expanded Laser Beam CCD Lens Sensor Test SLM Object

Constraints in conventional Hartmann Testing MetroLaser that can be obviated with this concept Irvine, California  Sensitivity requires a longer focal length which can cause focused image overlap of adjacent light pencils. > SLM enables scanning in time, NO OVERLAP  If the wave is aberrated, the focused spot will not be round, so its centroid is more difficult to locate, further reducing accuracy > SLM enables preconditioning/aberration correction  Spatial resolution is limited to the diameter of the lenses in the array. > Limited to fractional pixel size of SLM 6-7-2010-Monday Jtrolinger@metrolaserinc.com 13

Mandrel Used for Demonstration Photo of the Mandrel Geometry of the Mandrel Top diameter: 8.4” Cylinder lens Mandrel 6” Cone angle Bottom diameter: 8.2” • Mandrel provided by NASA GSFC, 6-inches tall, top and bottom diameters are different, cone shape. 6-7-2010-Monday Jtrolinger@metrolaserinc.com 14

MetroLaser Irvine, California System Design (Top view) Cylinder lens SLM PBS λ /4 BS polarizer Mandrel 1.0 meter Object beam Electronic s for SLM Top/Bottom λ /2 radius: λ /2 s 4.2/4.1 inch Pixelated Phasecam LCP Spatial filter, λ /4 HeNe Laser, 10mW 1.5 meter 6-7-2010-Monday Jtrolinger@metrolaserinc.com 15

MetroLaser Irvine, California The Hardware SLM 6-7-2010-Monday Jtrolinger@metrolaserinc.com 16

MetroLaser Irvine, California Simulation Results Interferogram Side View Beam size at cylinder lens: ~1.8inch 150mm fl cylinder lens Top view Cylinder lens Mandrel Mandrel Cylinder lens Coaxial position 6-7-2010-Monday Jtrolinger@metrolaserinc.com 17

Reducing the number of Fringes from a mandrel BS PBS SLM Beam size at cylinder lens: ~1.5inch. Pixel-cam 250mm fl cylinder lens used Laser (Various waveplates and telescopes not shown) Applied Phase on the SLM Residual Interferogram Measured Interferogram 4-13-2010-Tuesday 18

MetroLaser Irvine, California Compensation of one of Mandrel’s wavefronts for a one inch beam Before Compensation After Compensation 6-7-2010-Monday Jtrolinger@metrolaserinc.com 19

MetroLaser Resolution & Signal to Noise Irvine, California -Tilt by the flat mirror, ~7 waves Interferogram ~ 14 fringes Tilted Flat PBS BS Mirror SLM 3D view Pixel-cam Laser PV. ± 3.4 λ (Various waveplates and telescopes not shown) Tilt introduced by flat mirror 6-7-2010-Monday Jtrolinger@metrolaserinc.com 20

MetroLaser Irvine, California Resolution and Signal to Noise (Cont.) - Residual wavefronts, less than 0.05 λ Interferogram (3D view) Tilted Flat Mirror PBS BS SLM PV. ± 0.05 λ Pixel-cam x- profile Laser PV. ± 0.05 λ y- (Various waveplates and telescopes not shown) profile SLM can compensate tilted wavefronts with an accuracy of 1/20th wave, or better 6-7-2010-Monday Jtrolinger@metrolaserinc.com 21

MetroLaser Irvine, California Determining System Aberrations with a Cat’s Eye Due to SLM, cylinder lens, optical alignments, etc Coaxial position 6-7-2010-Monday Jtrolinger@metrolaserinc.com 22

MetroLaser Irvine, California Cat’s eye wavefronts by ZEMAX based on Experimental results Experimental measurement Leftover < 0.1 λ Simulated Fringes Fitted Zernike Polynomials upto 36 terms, found and put into Zemax Simulated Cats’ eye wavefronts by ZEMAX 6-7-2010-Monday Jtrolinger@metrolaserinc.com 23

MetroLaser Irvine, California Simulated, No System Aberrations Measured Top portion Top portion Beam : ~27mm Wavefronts at Wavefronts at Wavefronts at cat’s coaxial position at coaxial position at eye position at each each height each height height 24 6-7-2010-Monday Jtrolinger@metrolaserinc.com

MetroLaser Irvine, California Net fringe due to a Mandrel Cat’s eye Simulated Experimental Coaxial position position Net Fringes Net Fringes 6-7-2010-Monday Jtrolinger@metrolaserinc.com 25

MetroLaser Irvine, California Wavefronts from the Mandrel, II Simulated Wavefronts Experimental Wavefronts of the Mandrel Top Middle Bottom 6-7-2010-Monday Jtrolinger@metrolaserinc.com 26