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  • Detection of Light

    I. Introduction II. Solid State Physics

    4-2-2015 Detection of Light – Bernhard Brandl 1

  • 4-2-2015 Detection of Light – Bernhard Brandl 2

  • Blabla Recommended

    4-2-2015 Detection of Light – Bernhard Brandl 3

  • Information Carriers in Astronomy

    • In situ (planetary spacecraft)

    • Gravitational Waves

    • Neutrinos

    • Photons / electromagnetic waves

    4-2-2015 Detection of Light – Bernhard Brandl 4

  • The Electromagnetic Spectrum

    4-2-2015 Detection of Light – Bernhard Brandl 5

    Photons Waves

  • Light as a Wave

    4-2-2015 Detection of Light – Bernhard Brandl 6

    ( ) ( )00 rksinr 1,r φω +⋅−⋅= tEtE

    Angular frequency Wavenumber Intensity

    c k ω

    λ π ==

    2

    fπω 2=

    ( )20E∝

    Phase angle

    Space Time

  • Manifestation as Wave

    4-2-2015 Detection of Light – Bernhard Brandl 7

    1

    2

    2

    1

    2

    1

    v v

    sin sin

    :law sSnell'

    n n

    == θ θ

      

       +=

     

       +=

    c vv

    c v1or v1 00λλ

    Refraction

    Doppler effect (non-relativistic)

    Diffraction & interference

  • Light as a Particle

    Energy Momentum

    4-2-2015 Detection of Light – Bernhard Brandl 8

    λ ν hchE ==

    λ ν h c

    hp == ( )

    1exp

    12 5

    2

    −  

      

    =

    kT hc

    hcTI

    λ λλ

    Max Planck (1858 – 1947)

    Photoelectric effect –observed by Hertz (1887) and explained by Einstein (1905): light comes in “quanta”:

  • Information carried by Light …

    4-2-2015 Detection of Light – Bernhard Brandl 9

  • … and Measurements of that Information

    10

  • Detector Technology  Astronomy

  • 4-2-2015 Detection of Light – Bernhard Brandl 12

  • Two Fundamental Principles of Detection

    4-2-2015 Detection of Light – Bernhard Brandl 13

    Photons

    Waves

    Respond to electrical field strength and preserve phase

    Respond to individual photon energy

  • Two Types of Direct Detection

    Based on photoelectric effect (release of bound charges)

    4-2-2015 Detection of Light – Bernhard Brandl 14

    Thermalize photon energy

  • Wavelength  Technology

    4-2-2015 Detection of Light – Bernhard Brandl 15

    Quantum

    Thermal Coherent

  • 4-2-2015 Detection of Light – Bernhard Brandl 16

  • Lecture slides (“handouts”) will be posted on the site Homework and solutions will be posted on the site 4-2-2015 Detection of Light – Bernhard Brandl 17

    Course Topics & Lectures

  • Literature Main resource:

    Detection of Light - from the Ultraviolet to the Submillimeter, by George Rieke, 2nd Edition, 2003, Cambridge University Press, ISBN 0-521-01710-6.

    4-2-2015 Detection of Light – Bernhard Brandl 18

    Further reading: • Introduction to Solid State Physics (8th Edition)

    by Charles Kittel; • Electronic Imaging in Astronomy: Detectors and

    Instrumentation (2nd Edition) by Ian S. McLean; • Observational Astrophysics by P. Lena, Francoise Lebrun &

    Francois Mignard;

  • Course Organization

    • 3 ECTS, Level 500 – you need to register in uSis

    • Lecture room: Huygens #106/7 from 9:00 - 10:45 hr

    • Lecture period: 4 February – 1 April

    • Lecturer: Dr. Bernhard Brandl, office: #535

    • TA: Michael Wilby, office: #570

    • Grade = 80% written exam + 20% mandatory homeworks

    • Exam date: 13 April, 14:00 - 16:00 hr.

    4-2-2015 Detection of Light – Bernhard Brandl 19

  • Course Website http://home.strw.leidenuniv.nl/~brandl/DOL/Detection_of_Light.html

    4-2-2015 Detection of Light – Bernhard Brandl 20

  • 4-2-2015 Detection of Light – Bernhard Brandl 21

  • 4-2-2015 Detection of Light – Bernhard Brandl 23

  • Nucleons define the Period Table of the Elements

    4-2-2015 Detection of Light – Bernhard Brandl 24

  • Electrons lead to Atomic Lines and Bands

    4-2-2015 Detection of Light – Bernhard Brandl 25

    • Electrons are described by probability clouds (“orbitals”) with specific energies.

    • An electron around a positively charged nucleus has one unique set of four quantum numbers (QN).

    Principal QN (n) = electron shell

    Orbital QN (l) = angular momentum

    Magnetic QN (ml)

    Spin QN (ms)

  • Electronic Energy Levels

    4-2-2015 Detection of Light – Bernhard Brandl 26

    • An atom can absorb or emit photons of specific energies • In this process, electrons change their energy levels (“orbitals”)

    Example: hydrogen atom with one electron

  • 4-2-2015 Detection of Light – Bernhard Brandl 27

  • Electronic Bonding

    4-2-2015 Detection of Light – Bernhard Brandl 28

    This can lead to transfer of electrons ( salts) or sharing of electrons ( covalent bonds)

    Atoms with “incomplete” (= less than eight electrons) outer shells want to form a stable configuration

  • The Diamond Lattice Elements with 4 e– (e.g., C, Si, Ge) form crystals with a diamond lattice structure (each atom bonds to four neighbors).

    4-2-2015 Detection of Light – Bernhard Brandl 29

  • III – IV Semiconductors A diamond lattice can not only be formed by IV elements (C, Si, Ge) but also by elements from the 3rd and 5th group of elements.

    4-2-2015 Detection of Light – Bernhard Brandl 30

    Gallium has 3 electrons, Arsenic has 5 electrons:

    Si GaAs

  • Common Semiconductor Materials

    4-2-2015 Detection of Light – Bernhard Brandl 31

  • 4-2-2015 Detection of Light – Bernhard Brandl 32

  • Metals, Semiconductors and Insulators

    Metals have high electrical conductivity and consist of positive ions in a crystal lattice surrounded by delocalized electrons. Semiconductors have electrical resistivity between metals and insulators, which is temperature dependent. Insulators (also called dielectrics) resist the flow of electric current.

    4-2-2015 Detection of Light – Bernhard Brandl 33

    Metals

    Semimetals

    Semiconductors

  • Animation: Electronic States and Bands Link to file

    4-2-2015 Detection of Light – Bernhard Brandl 34

    http://en.wikipedia.org/wiki/Electronic_band_structure

  • Atomic Orbitals overlap  Electronic Bands

    4-2-2015 Detection of Light – Bernhard Brandl 35

    Isolated atoms Lattice spacing Decreasing atomic separation

    VALENCE BAND

    CONDUCTION BAND

    Energy Outermost orbitals begin to

    overlap.... ...bands form at crystal spacing

  • Bands in a periodic Crystal Lattice

    4-2-2015 Detection of Light – Bernhard Brandl 36

    *note that even in a crystal with T=0, the electrons have momentum

    The so-called k-vector of an electron or hole in a crystal is the wave- vector of its quantum-mechanical wavefunction

    The electron moves* with momentum in a periodic lattice with lattice constant a and potential U.

    kp =

    Atom Crystal

  • Real Band Structures

    "Bulkbandstructure" by Saumitra R Mehrotra & Gerhard Klimeck - Bandstructure Lab on nanoHUB.org Link: http://nanohub.org/resources/8814. Licensed under CC BY 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Bulkbandstructure.gif#mediaviewer/File:Bulkbandstructure.gif

    4-2-2015 Detection of Light – Bernhard Brandl 37

  • Band Gaps of Isolators, Metals and Semiconductors

    4-2-2015 Detection of Light – Bernhard Brandl 38

    Energy CONDUCTION BAND

    VALENCE BAND

    BAND GAP

    Insulator Metal Intrinsic Semiconductor

  • What makes a Detector work …:

    That photon of energy may be our astronomical signal.

    However, note that electrons can also get thermally excited  cooling 4-2-2015 Detection of Light – Bernhard Brandl 39

    Energy CONDUCTION BAND

    VALENCE BAND

    BAND GAP

  • 4-2-2015 Detection of Light – Bernhard Brandl 40

  • The Fermi Energy In a 1D, periodic potential, the electronic energy states are given

    by

    4-2-2015 Detection of Light – Bernhard Brandl 41

    At T = 0 K the Fermi energy is the same as the chemical potential µ.

    22

    2   

      =

    a n

    m En

    π

    The Pauli principle requires that no two electrons have exactly the same quantum numbers.

    The energy corresponding t

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