1. 10/26/20151 Observational Astrophysics I Astronomical detectors Kitchin pp. 2-51

2. 10/26/20152 Types of detectors Integrating detectorsPhoton counting detectors (PCD) Accumulate reaction to incoming radiation over time React to (almost) every incoming photon and produce digital count Example: photographic plate, CCD Example: photomultiplier

3. 10/26/20153 Common parameters 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 Dark current Memory Flatness

4. 10/26/20154 Charge Coupled Device Light Parallel charge transport Serial charge transport towards ADC

5. 10/26/20155 Readout sequence

6. 10/26/20156 Continuous flow cryostat

7. 10/26/20157 Electron trail

8. 10/26/20158 Critical data flow properties 12 or 16 bits CCD Parallel CTE Serial CTE Logarithmic amplifier Analog signal Digital signal ADUs ADC+ bias Readout noise Temperature control Voltage on shift register

9. 10/26/20159 Quantum Efficiency

10. 10/26/201510 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. 10/26/201511 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. 10/26/201512 Cooling Liquid N 2 : 125  150 K Peltier cooler: -20°  -60° C

13. 10/26/201513 Cosmetics

14. 10/26/201514 Fringing λ=650 nmλ=900 nm

15. 10/26/201515 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. 10/26/201516 Modulation Transfer Function MTF characterizes interplay between contrast and spatial sampling

17. 10/26/201517 Charge Transfer Efficiency This is examined by measuring the amplitude of bright points left by a  –ray source. Amplitude dependence in the direction of parallel read gives parallel CTE, while the other direction reflects serial CTE. Good CTE is >0.99999. The same experiment establishes the relation between ADU and number of photoelectrons (gain). Same CCD may use more than one gain (e.g. 1.1 and 9).

18. 10/26/201518 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 destroy content of a few pixels

19. 10/26/201519 Flatness

20. 10/26/201520 Binning Step 1Step 2Step 3Step 4 Readout Example: 4  4 binning Exposure

21. 10/26/201521 Next time… Hybrid detectors IR detectors Photon counting detectors Calibrations