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    Basic Principles of Lasers

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    Basic Principles of Lasers

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    laser

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    laser

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    76 views21 pages

    Basic Principles of Lasers

    Uploaded by

    geerthanaraj
    laser

    Copyright:

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    Download as PDF, TXT or read online from Scribd
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    Presentation for an Honors Contract Spring 2007 Modern Physics

    Basic Principles of Lasers


    Presentation By: Zack Hansel

    Instructor: Dr. Cristian Bahrim

    Summary
    Classification of light-atom interaction. Necessary conditions for a lasing transition. Standard lasing systems: - three-level atom system, - four-level atom system. Properties of a laser. Types and uses of lasers.
    2

    Classification of Light-atom Interaction


    Stimulated absorption + h > Spontaneous emission > + h Stimulated emission + h > + 2h

    The Cascade of Photons

    Energy Distribution
    For No atoms in thermal equilibrium at temperature T the population of atoms Nj on the j-state is

    Nj=Noexp(-Ej/kT)

    (Boltzman distribution)

    where kT represents the mean energy of the atoms.


    8 7 6 Population 5 4 3 2 1 0 2 4 6 8 10 12 14 16 18 20

    (N2; E2) (N1; E1) (N2; E2)


    Energy

    (N1; E1)

    Ground state

    Understanding the Lasing Process


    LASER Light Amplification by Stimulated Emission of Radiation Necessary conditions for a lasing transition: - population inversion, - metastable states.
    6

    Population Inversion
    8 7 6 P o p u l a ti o n 5 4 3 2 1 0 2 4

    Metastable States

    (N2; E2)

    (N1; E1)
    6 8 10 12 14 16 18 20 Energy

    Long-lived state (~1 ms) (N2; E2) Laser beam (N1; E1) Short-lived state (~1 ns) Spontaneous Ground state
    7

    Three-level Atom
    E3 PUMPING E2

    E1

    Example: Ruby laser (uses Cr++ ions) Deficiency Photons may be re-absorbed during the lasing process > it makes the laser beam weaker.

    The build-up of a Laser 1) Pumping (excitation of atoms)

    2) Stimulated emission of atoms 3) The lasing process is enriched by multiple reflections between mirrors 4) A laser beam exits.
    9

    Ruby Laser
    Developed by Theodore H. Maiman in 1960 Creates a beam at = 694 nm (deep red). Metastable state of ~3ms Has efficiency of less than 1% but creates a diameter ranging from 1 mm to about 25 mm, so a large energy density is achieved in the laser beam.

    10

    Four-level Atom
    Example: HeNe laser

    PUMPING

    PUMPING

    11

    Properties of a Laser
    Monochromaticity same or frequency Directivity Highly correlated photons for long distances. High energy-density Polarization Modes

    12

    Resonant Cavity

    HeNe

    13

    Modes of Lasers
    Mono-mode laser Gaussian profile

    Multimode lasers

    14

    Types of Lasers
    Gaseous laser : - atomic gaseous lasers (e.g. HeNe) - molecular laser (e.g. CO2) Dye laser (e.g. N2 - rhodamine) Electronic laser (uses the acceleration of electrons) Solid laser semiconductor (YAG-Nd laser) Atomic laser Bose-Einstein condensate.

    15

    HeNe Laser

    16

    A Look at Laser Sizes

    Dye Laser Wavelengths

    17

    YAG-Nd Laser

    Electronic Laser

    18

    Comparisons of a Few Lasers


    Laser HeNe CO2 Dye Typical Range Pulse or CW CW CW Usually Pulse 1.15m-633nm IR-Visible 9.4-10.6m 360-720nm IR IR-UV

    Electronic 1mm-1nm YAG:Nd 940-1440nm

    Microwaves CW -X-rays IR Both


    19

    The use of Lasers


    Science precise measurements, spectroscopy Medicine laser scalpel, eye surgery Industry cutting and welding, guidance systems Arts etching Telecommunications (fiber optics) Radars Precise measurement of long distances (e.g. Moon) Consumer CDs, DVDs, laser lights
    20

    Resources
    Modern Physics, Kenneth Krane, 2nd ed., John Wiley & Sons, Inc. (1996). Introduction to Laser Physics, Koichi Shimoda, Springer-Verlag (1984). Optics, Eugene Hecht, 4th ed., Addison Wesley (2002). Sams Laser FAQ, Samuel Goldwasser, http://www.repairfaq.org/sam/lasersam.htm. Wikipedia, www.wikipedia.org
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