ASTR633 Astrophysical Techniques Course slides Chapter 3: - - PowerPoint PPT Presentation

ASTR633 Astrophysical Techniques Course slides

Chapter 3: Detectors

Fundamental principle is for light-detecting material to absorb a photon and thereby release one (or more) electrons, which is then detected. Optical array detectors (CCDs) became widespread in 1980s (Nobel Prize in 2009 to its inventors), and near-IR array detectors in the 1990s. Optical:

• Light-detecting material is silicon, sensitive from 0.3-1.1 µm.
• Largest individual arrays are 6K x 6K, though “arrays of arrays” (a.k.a. mosaics) are

common, e.g. Keck/LRIS has two 2K x 4K with no gaps (buttable).

• Largest camera is Pan-STARRS1 GPC, 64 x 64 mosaic of 600 x 600 pixels = 1.4

Gigapixels Near-IR:

• Two common choices of material are HgCdTe (0.8-2.5 um) and InSb (0.8-5.5 um).
• Largest individual arrays are Hawaii-4RG = 4096 x 4096 pixels = 17 million pixels
• Largest mosaic is UK’s VISTA camera, with 16 2K x 2K arrays = 67 million pixels.

However, IR arrays are not buttable due to readout electronics so IR mosaics have gaps.

Figure 3.1 What are valence and conduction bands?

Figure 3.2

Crystal structure for semi-conductors

Figure 3.3

Bandgap diagrams

Figure 3.4

Absorption coefficients

Noise

• Johnson-Nyquist noise
• Dark current
• Read noise

Describe each one and how to mitigate their effects

Figure 3.5 What is the dynamic range?

Figure 3.7

Physical arrangement of Si:As detector

Figure 3.8

Band diagram

Figure 3.10

Photodiodes

Oppositely doped semiconductors adjacent to each other

Figure 3.16

Charge Coupled Devices

Figure 3.17

CCD Readout

Well depth ~ 105 electrons Each pixel consists of 3 electrodes

https://commons.wikimedia.org/wiki/File:CCD_charge_transfer_animation.gif

Figure 3.18

CCD Readout

Veiga et al. 1998, A&A Suppl., 136, 455

Tonry et al. 1997

Figure 3.23

Image Intensifier