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CCD’s (Charge Coupled Devices)

CCD’s (Charge Coupled Devices). An Imaging Technology in “Visible” Light Marino Maiorino – - Dec. 1 st 2006 15:00 – Downstairs Meeting Room. Summary. Introduction The Birth of New Technologies CCD Features Technological Limitations Basic Data Manipulation IFAE and CCD’s

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CCD’s (Charge Coupled Devices)

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  1. CCD’s(Charge Coupled Devices) An Imaging Technology in “Visible” Light Marino Maiorino – - Dec. 1st 2006 15:00 – Downstairs Meeting Room

  2. Summary • Introduction • The Birth of New Technologies • CCD Features • Technological Limitations • Basic Data Manipulation • IFAE and CCD’s • Improper Applications • Alternative Technologies • Latest Developments CCD's

  3. Introduction • On Visible and Optical Wavelengths • Image Recording Techniques • Transition between film and Solid-State detectors • Digital revolution • Astronomical Imaging With Film • “Telescopes do NOT magnify; they get more light!” – Massimo Capaccioli CCD's

  4. On Visible and Optical Wavelengths(Introduction) • Visible (380 ÷ 750 nm) • What is visible to the human eye • Optical (300 ÷ 1000 nm) • Includes some UV and IR • Range of wavelengths where optics laws apply CCD's

  5. Naked Eye Observation(Image Recording Techniques) • 6 Mcones • 200 Mrods • Logarithmic sensor • Daylight (Photopic) vision • Nighttime (Scotopic) vision CCD's

  6. Naked Eye Observations(Image Recording Techniques) CCD's

  7. Incident photons Silver Emulsion Film Film(Image Recording Techniques) Allows • Objective Measurements • Light Integration Features • Higher Quantum Eff. • Broader Spectral Allowance CCD's

  8. Film(Image Recording Techniques) • Reciprocity failure • Exp. ∝ Aperture × ShutterTime × FilmSpeed • The law of reciprocity: golden rule of photography. Defines the relationship between shutter time, aperture, and film speed with respect to an exposure • Changes to any of the latter three elements are done in “stops”. A stop is equal to a factor of 2 CCD's

  9. Film(Image Recording Techniques) Unsharp Masking • A form of photographic alchemy • Subtract a blurred image to the original • Enhance the local contrast CCD's

  10. Solid-State Detectors(Image Recording Techniques) • An incoming photon kicks an electron in the conduction band • The read-out system gives you a digital signal, which can be numerically processed! CCD's

  11. Astronomical Imaging with Film(Introduction) • Special film or photographic plates • A method to combat reciprocity failure is gas-hypering: the film is soaked in a mixture of hydrogen and nitrogen gas at elevated temperatures for prolonged periods before exposure • Very long exposure times (hours) • Filtered Imaging • Chemical Development CCD's

  12. The Birth of New Technologies • CCD (Charge-Coupled Devices) • CMOS (Complementary Metal Oxide Semiconductors) • Comparing Technologies • Companies Rule CCD's

  13. CCD (Charge-Coupled Devices) (The Birth of New Technologies) • Willard Boyle and George Smith, 1969, Bell Labs • Working on the “bubble memories” • Silicon is sensitive to light • If exposed to light, one can grab images CCD's

  14. Charge Amplifier CCD (Charge-Coupled Devices) (The Birth of New Technologies) Bucket Brigade • Integration • Charge Shift and Read-out CCD's

  15. CMOS(The Birth of New Technologies) • Every pixel has its own charge-to-voltage converter • Sensor often also includes: • Amplifiers • Noise-correction circuitry • Digitization circuitry • The chip outputs digital bits • Increased design complexity • Reduced area for light capture • As each pixel does its own conversion, uniformity is lower • The chip can be built to require less off-chip circuitry for basic operation (camera on a chip) CCD's

  16. Film vs. CCD(Comparing Technologies) Film CCD • reciprocity failure beyond a few second exposure • no loss of sensitivity to light during exposure • minimal light intensity required to detect a target at all • no minimal light intensity needed to detect a target • low quantum efficiency (max. 4% at optimal wavelengths) • high efficiency of light detection (up to 90%, though device- and wavelength-dependent) • response to light is non-linear • signal is proportional to light intensity • small dynamic range (6-bit) • large dynamic range (typically 16-bit) • picture elements (grain) are randomly distributed • picture elements (pixels) are regularly spaced • ready for digital processing • needs to be processed in a chemical darkroom CCD's

  17. Film vs. CCD(Comparing Technologies) CCD's

  18. Film vs. CCD(Comparing Technologies) CCD's

  19. CCD vs. CMOS(Comparing Technologies) CCD's

  20. Companies Rule(The Birth of New Technologies) • Commercial Requirements (fast read-out time, high noise) • (HAD)  • (CMOS) • (Super CCD) CCD's

  21. Trichromy(Companies Rule) • Color Filter Array (CFA), by Dr. Bryce Bayer, Kodak, 1970 • Where not available, color values are interpolated CCD's

  22. Device Shape(Companies Rule) • Ideal shapes: • Square (easy to manufacture) • Hexagonal (use most of focal plane area) • Circular (use all of the focal plane area) • Typical Width to Height factor is 4:3 (TV, PC monitors, etc.) CCD's

  23. (Companies Rule) • Color Filter Array (CFA), 1970 • Transparent Gate Technology, 1998 (aka Blue Plus) to improve device sensitivity • They even sell you evaluation boards, or you can build them on your own! http://www.kodak.com/ezpres/business/ccd/global/plugins/acrobat/en/eval/KodakAreaArrayCCDTimingGenerator.pdf CCD's

  24. (Companies Rule) HAD (Hole Accumulated Diode) • Technique to reduce electronic noise by reducing the “dark” current. • The holes created by heat or imperfections in the creation of the imaging chip are accumulated in a separate semiconductor layer that acts as a diode and prevents them from returning or creating noise. Microlenses layers CCD's

  25. -(Companies Rule) • Three CCD’s Trichromy • Philips trichroic beam-splitter CCD's

  26. (Companies Rule) • Introducing CMOS devices with a 3:2 factor (compatible with old fashioned film) • EOS 1Ds Mark II, 16.7 Mpxl sports a 36×24mm sensor CCD's

  27. Fujifilm - SuperCCD(Companies Rule) CCD's

  28. CCD Features Kodak KAF-1001 CCD's

  29. Charge Transfer Efficiency(CCD Features) • Kodak KAF-1001 features a 1024×1024 image matrix • CTE > 0.99997 at –40 °C • If xs, ys is the horizontal/vertical position of a pixel in the CCD matrix, charge being read by the read-out amplifier is Qreadout = Qpixel·CTE(xs +ys) • The farthest pixel from the amplifier loses 6% of its charge • If CTE = 0.999  loss = 87%!!! CCD's

  30. Absorption Depth in Si (90%) Wavelength (nm) Depth (µm) 400 0.19 450 1.0 500 2.3 550 3.3 600 5.0 650 7.6 700 8.5 750 16 800 23 850 46 900 62 950 150 1000 470 1050 1500 1100 7600 Sensitivity Improvements(CCD Features) • Front-Illuminated CCD’s • Back Illuminated (Back-Thinned) – Higher QE, Wider illuminated area, Semi-transparent to NIR • Deep Depletion (deeper photoactive region) • Electron Multiplying CCD’s – A gain amplifier is put before the output amplifier (avalanche diode) CCD's

  31. Technological Limitations • Noise Sources: • CCD — output stage kT/C-noise • Semiconductor Noise — Shot, Flicker, White Noise • Resistor / Thermal Noise • ADC Quantization Noise • Line Frequency, 50/60 Hz • Blooming • Effective Energy Resolution • Spectral “Insensitivity” • Time “insensitivity” CCD's

  32. Noise Sources(Technological Limitations) • Blind Frame around the central sensor • Cool the sensor (-40 °C) • Take a dark frame image and subtract it from real images - = CCD's

  33. Blooming(Technological Limitations) • The charge generated into a pixel “spills” over to the neighbouring ones. • At readout time, this charge can be found in the pixels along one column/raw • Can be cured by introducing an anti-blooming drain gate CCD's

  34. Effective Energy Resolution(Technological Limitations) • The energy needed to kick an electron in the conduction band, in Si, is at least 1.12eV (≈1100 nm, far IR) • This is very good for far UV, X-rays and γ-rays (from 100 eV and beyond), but useless in visible (300 nm = 4.1eV) • Read-out noise (~ 10 e-) limits any serious discussion about the topic in visible light CCD's

  35. Spectral “Insensitivity”(Technological Limitations) • A time-integrated image contains electrons generated by photons of different energies • How to discriminate among them? CCD's

  36. Time “Insensitivity”(Technological Limitations) • Dark subjects require long exposure times • Time-integrated images contain electrons generated by photons arrived at different times • Gamma ray bursts and other phenomena may require much higher time resolution CCD's

  37. Basic Data Manipulation • Dark Frame Acquisition • Flat Field Acquisition • Image Acquisition • Noise Subtraction • Gain Adjustment CCD's

  38. Basic Data Manipulation For multi-band images, repeat the processing for any “monochrome” image, then stack them CCD's

  39. IFAE and CCD’s • DES (Dark Energy Survey) • 500 Megapixel camera, DAQ system fast enough to take images in 17 seconds • Galaxy Cluster counting - 20,000 clusters to z=1 with M > 2x1014 M • Weak lensing - 300 million galaxies with shape measurements over 5000 sq deg. • Spatial clustering of galaxies - 300 million galaxies to z = 1 and beyond • Standard Candles - 2000 SN Ia, z = 0.3÷0.8 • Multi-bandpass wide area survey, designed to produce photometric redshifts from 0.2 < z < 1.3 CCD's

  40. Band λ (µm) Δλ/λ U 0.36 0.15 B 0.44 0.22 V 0.55 0.16 R 0.64 0.23 I 0.79 0.19 J 1.26 0.16 H 1.60 0.23 K 2.22 0.23 g 0.52 0.14 r 0.67 0.14 i 0.79 0.16 z 0.91 0.13 g, r, i, z Photometry(IFAE and CCD’s) • Gunn griz System was originally defined in terms of photoelectric detectors (Thuan & Gunn 1976; Wade et al. 1979), but is now used primarily with CCD’s • It is defined by a few dozen standard stars • The star BD+17deg4708, an F6 subdwarf with B-V=0.43, is defined to have colors equal to zero CCD's

  41. DES CCD’s(IFAE and CCD’s) • 4096×2048 pixel • Square pixels, 15µm size • Resolution: 0.27”/pixel • Back-thinned • CTE < 0.99999 (Lose at most 6%) • Noise < 5 e- CCD's

  42. 3556 mm Camera 1575 mm Scroll Shutter Filters Optical Lenses 2.2 deg. FOV DES CCD’s(IFAE and CCD’s) CCD's

  43. Improper Applications X-ray Imagers (Astrophysics, Medicine) • Cover the sensor with some fluorescent material • High energy photons get absorbed and re-emit at lower energy Single-photon counting (far UV, X- and γ–rays) • Make sure that the number of photons per unit time is AT MOST 1 per pixel • Take one image per unit time • The charge measured per pixel is directly proportional to the incoming photon energy CCD's

  44. Latest Developments Multi-Layer Sensors • Originally, an April fish about CANON, in 2000 • It was actually under development at FOVEON and released in 2002 • CMOS technology • Principle: silicon absorbs different wavelengths at different depths • 100% of light, captured • No colour interpolation needed • Sigma, Polaroid and Hanvision products feature this technology CCD's

  45. Alternative Technologies Scientists want a device with: • “Reasonable” noise (i.e.:  Poisson limit) • “Reasonable” sensitivity (i.e:  100%) • “Reasonable” space resolution (i.e.:  diffraction limited) • “Reasonable” spectral resolution (i.e.:  ΔE/E < 0.1%) • “Reasonable” time resolution (i.e.:  0 ps) CCD's

  46. Bibliography & Web References • http://aberrator.astronomy.net/moon/index.html • http://ncmi.bcm.tmc.edu/ncmi/events/workshops/workshops_53/proceeding/2005July26_DetectingElectronsLecture.ppt • http://home.earthlink.net/~kitathome/LunarLight/moonlight_gallery/technique/reciprocity.htm • http://www.lumigen.com/documents/CL_measure.shtml • http://www.olympusfluoview.com/theory/detectorsintro.html • http://angryastronomer.blogspot.com/2006/06/astronomical-data-2b-light-detection.html • http://www.fvastro.org/presentations/ImagingFilm/Imaging%20with%20Film.pdf • http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/concepts.html • http://www.astrosurf.com/jwisn/deepsky.htm • http://en.wikipedia.org/wiki/Science_of_photography CCD's

  47. Bibliography & Web References • http://www.avaloninst.com/content/raman_information/glossary.htm • http://fy.chalmers.se/astro/master/vl/lp1/photfilters.pdf • http://www.cs.wisc.edu/graphics/Courses/559-s2002/lectures/cs559-2.ppt • http://www.kodak.com/US/en/dpq/site/SENSORS/name/ISSHome • http://www.canon.com/technology/canon_tech/explanation/cmos.html • http://www.fujifilm.com/about/technology/super_ccd/ • http://www.fujifilm.com/news/n030122.html • http://www.telescope-service.com/atik/start/atikstart.html • http://soho.estec.esa.nl • http://starizona.com/acb/ccd/advtheorycolor.aspx • http://www.astrosurf.com/re/index.html CCD's

  48. Bibliography & Web References • http://www.foveon.com/article.php?a=67 • https://www.darkenergysurvey.org/ • http://www.astro.utoronto.ca/~patton/astro/mags.html • http://ulisse.pd.astro.it/Astro/ADPS/Systems/index.html • Ron Wodaski, “The New CCD Astronomy” CCD's

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