1 / 20

Observational Astrophysics I

Observational Astrophysics I. Astronomical detectors Kitchin pp. 2-51. Types of detectors. Quantum efficiency (QE) Spectral response Linearity Gain Dynamic range Saturation level Cosmic ray sensitivity. Modulation Transfer Function (MTF) Cosmetics Noise Shot noise Read-out noise

javier
Download Presentation

Observational Astrophysics I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Observational Astrophysics I Astronomical detectors Kitchin pp. 2-51

  2. Types of detectors

  3. Quantum efficiency (QE) Spectral response Linearity Gain Dynamic range Saturation level Cosmic ray sensitivity Modulation Transfer Function (MTF) Cosmetics Noise Shot noise Read-out noise Dark current Memory Flatness Common parameters of detectors

  4. Light Serial charge transport towards ADC Parallel charge transport Charge Coupled Device

  5. Readout sequence

  6. Continuous flow cryostat

  7. Electron trail

  8. Parallel CTE Digital signal ADUs Voltage on shift register Temperaturecontrol CCD Serial CTE Readoutnoise + bias ADC Logarithmicamplifier Analog signal Critical data flow properties 12 or 16 bits

  9. Quantum Efficiency

  10. Improving spectral range • QE drops in the blue because the top layer is too thick and non-transparent. One way to improve it is the remove extra silicon substrate from the back (thinning) and use this side to detect the light (back-illumination). • QE drops in the red because photons have too low energy. Warming up CCD improves response in the red but also increases the noise.

  11. Dark current At T=270 K DC 10 e-/pixel/s At T=230 K DC 0.1 e-/pixel/s At T=170 K DC 10 e-/pixel/hour At T=120 K DC 1 e-/pixel/hour

  12. Cooling Peltier cooler: -20°  -60° C Liquid N2: 125  150 K

  13. Cosmetics

  14. Fringing λ=650 nm λ=900 nm

  15. Linearity CCD full well is the number of electrons which can be stored in one pixel (height of energy barrier between pixels).Typical values are between 30000 and 1000000 which also where the CCD goes non-linear.

  16. Charge Transfer Efficiency • This is examined by measuring the amplitude of bright points left by a –ray source. Amplitude dependence in the directionof parallel read gives parallelCTE, while the other directionreflects serial CTE. Good CTEis >0.99999. • The same experimentestablishes the relation betweenADU and number of photoelectrons (gain). Same CCD may use more than one gain (e.g. 1.1 and 9).

  17. CCD noise • Shot noise (Poisson distribution σ≈√N) • Dark current is time, depends on temperature • Readout noise, depends on the temperature, read speed and amplifier(s) used • Cosmic rays destroycontent of a few pixels

  18. Flatness

  19. Binning Example: 44 binning Readout Exposure Step 1 Step 2 Step 3 Step 4

  20. Next time… • Hybrid detectors • IR detectors • Photon counting detectors • Calibrations

More Related