Overview
●Photographic Plates
●The Photoelectric Effect
●Photomultiplier Tube Basics
●CCD Basics: Structure and Operation
●Quantum Efficiency
●Binning
●System Gain
●Noise Sources
●Optimal Data and Calibration Images
●Data Reduction Basics
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community
Ask the community for help and clear up your study doubts
University Rankings
Discover the best universities in your country according to Docsity users
Free resources
Our save-the-student-ebooks!
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
The Photoelectric Effect - Lecture Slides | SPS 2010, Study notes of Aerospace Engineering
Material Type: Notes; Professor: Perlman; Class: Observational Astronomy; Subject: Space Sciences; University: Florida Institute of Technology; Term: Spring 2010;
Typology: Study notes
2009/2010
1 / 23
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download The Photoelectric Effect - Lecture Slides | SPS 2010 and more Study notes Aerospace Engineering in PDF only on Docsity!
Overview
● Photographic Plates ● The Photoelectric Effect ● Photomultiplier Tube Basics ● CCD Basics: Structure and Operation ● Quantum Efficiency ● Binning ● System Gain ● Noise Sources ● Optimal Data and Calibration Images ● Data Reduction Basics
Photographic Plates
● Used historically ● Wide FOV, high resolution ● But terrible Quantum Efficiency (QE ~ 1%)
- QE = (#photons detected) / (#photons incident) x 100
- QE = 100% means you count every photon that hits detector. ● Non linear behavior, so difficult to get good magnitudes using plates ● Photographic plates no longer used at major observatories
Photomultiplier Tube Basics
● “Electron multiplier phototube” = “photomultiplier tube” ● Basic need: single electrons released via photoelectric effect can’t be measured, so stack a series of plates, and let electrons cascade
- Photon releases electron at cathode
- A dynode is placed close, and with a potential difference of ~100V. When electron strikes the dynode, 2-3 electrons are released.
- Stack several dynodes, and finally detect pulse of ~ 6 electrons at the Anode
PMT Applications
- Historically, preferred to photographic plates for measuring magnitudes
- High time-resolution astronomy (still beats CCDs in this area)
- Describe 3-star photometer …
Sources of Noise
● Dark Current / Thermal noise ● Random pulse sizes ● Cosmic Rays ● Magnetic Fields (use μ-metal) ● Also, aging from vacuum leakage, bright illumination ● Keep in light-tight enclosure
Photoelectric Effect in
Semiconductors
- Atomic Energy levels perturbed if nearby atoms
- Split to 2 levels if 2 atoms
- N levels if N atoms -> BAND structure
Photoelectric Effect in
Semiconductors
- In semiconductor, there is only a small gap between valence and conduction band
- Thermal motions, photon absorption can excite e- to conduction band.
- Once in conduction band, the e- can move through the semiconductor, for example towards an electrode with +charge
CCD Basics
● Physical Structure ● Transferring Charges ● Binning (Figures from Apogee ccd.com website)
Basic Structure: Array
- Array of pixels with insulators between (high p-type doping)
- Each develops charge proportional to illumination intensity
- Now just need to read it out
Multiple Electrodes &
Charge Transfer
- If charge is under B, and all A-D are at +10V, then charge will diffuse to be equal under all 4
- If A and C kept at +2V, though, then charge remains under B
- This allows us to transfer charge
- Charge transfer efficiency 99.999%
Quantum Efficiency
● QE = (#photons detected) / (# photons Incident) The closer to 100% the better! Detector absolutely needs to be linear for you to do photometry Note: Different sensitivities at different wavelengths, so must calibrate through each filter. Also, must integrate longer for same S/N in regions with lower QE.
Sources of Noise
- Readout Noise: Imperfect repeatability when charge read through A/D converter, and other unwanted counts from electronics
- Dark current: Thermal motions of atoms bump electrons into valence band – lower temp for lower dark current