SPIcam: an overview. Alan Diercks Institute for Systems Biology 23rd July 2002

Transcription

1 SPIcam: an overview Alan Diercks Institute for Systems Biology 23rd July 2002

2 1 Outline Overview of instrument CCDs mechanics instrument control performance construction anecdotes

3 Apache Point Observatory 2

4 3.5-meter telescope 3

5 4 Light Path secondary mirror rotator tertiary mirror SPIcam primary mirror

6 5 axis controllers dewar camera control electronics rotator CCD cooling head data transmission waste heat closed cycle cooler (CryoTiger) temperature control (Lakeshore) telescope control computer data interface control computer remote workstation

7 6 Charge-Coupled-Devices (CCDs) near-perfect detectors for optical radiation high quantum efficiency 100% fill-factor large linear dynamic range few electrons (photons) read-noise negligible dark-current

8 CCD structure 7

9 CCD layout 8

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11 10 Quantum Efficiency blue cut-off results from short penetration depth of photons through gate structure red cut-off results from band-gap of silicon (1.14 ev = 1085 nm, at 173 K)

12 CCD quantum efficiency 11

13 Front-side vs. back-side illumination 12

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21 20 Dynamic Range determined by the full well depth of the device scales approximately with pixel volume 200, 000 e for SPIcam CCD ( 60, 000ADU) newer CCDs with read noise 1e (> 16-bit dynamic range)

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23 22 Read Noise usually dominated by the properties of the on-chip amplifier scales as readout rate typically 3-8 e for scientific CCDs newer devices are approaching sub-electron read noise

24 CCD readout 23

25 Dark Current 24

26 25 Mechanical Design: Internal position detector rigidly with respect to optical path transfer mechanical registration from inside to outside of dewar thermally isolate detector from environment keep vacuum environment as clean as possible bring first-stage output amplifier as close to the detector as possible

27 26 window dewar lid reference surface CCD fiberglass spring cooling block cold strap cold head

28 27 positioning detector f/10 beam of 3.5-meter has 700µm depth-of-focus calibrated contact to cooling head allow for thermal contraction on cooling = fiberglass spring

29 28 Cryogenics cool to 100 C eliminate need for liquid nitrogen ion-pump is useful reduce workload on observatory staff

30 CryoTiger 29

31 CryoTiger 30

32 31 Mechanical Design: External shutter filter wheel electronics waste-heat control

33 32 Rotating-Wheel Shutter small slit CCD large slit

34 Shutter Timing 33

35 34 Filter Wheel must work read-back of wheel position holds 6 filters position filters to few microns minimize handling of filters

36 35

37 36 Electronics Packaging robust against electrical interference minimize cable lengths to dewar lightning protection

38 37 Simplified Grounding Scheme Dewar CCD analog electronics "earth ground" "earth ground" fiber optic link control computer

39 38 Waste-Heat Removal forced-air heat removal from electronics packages dump heat to mid-level makes a good vacuum-cleaner

40 39 Electronics based on architecture developed by Peter Doherty at Photometrics 6811 = DSP = level-shifter = clock wave-forms 6811 also controls shutter and filter-wheel 40 khz pixel rate parallel data is serialized for transmission to control computer

41 40 Software control unix workstation for ease of networking command-line interface scripting in mana (Gene Magnier) instrument sends commands directly to TCC scripts for taking focus images, sky-flats automatic focus adjustment when changing filters

42 41 Software architecture motor controllers SPIcam telescope control computer (TCC) electronics package data on fiber serial on fiber dryrot.apo.nmsu.edu (Sparc 5) Master Control Computer (MC) internet Remark Interface (Mac) remote workstation

43 42 Performance 25 sec. full-frame read-time (binned 2 2) 4.78 arcminute F.O.V. at 0.14 arcsec per pixel 3.37 e / ADU sensitivity 5.7 e read-noise, 2.7 e /hr dark current CTE in both serial and parallel directions

44 43 Sensitivity - Sloan Filter Star Sky (per pixel) u* g* r* i* z* m = 20, 1 sec. integration, binned 2 2, area is 4πσ 2 for Gaussian PSF

45 44 Sensitivity - Johnson-Cousins Filter Star (e /s) Sky (e /s/pixel) U B V R I m = 20, 1 sec. integration, binned 2 2, area is 4πσ 2 for Gaussian PSF

46 45 Anecdotes from SPIcam construction know when to wing it monitor everything efficiency of operation is critical always carry tools roads in New Mexico are rough