Lasers and Optics
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Questions and Answers

What is a characteristic of the output of gas lasers?

  • High monochromaticity and high stability of frequency (correct)
  • High output power
  • Pulsed duration of microseconds
  • Full-spectrum white light

    • What is the pumping method used in He-Ne lasers?

  • Chemical pumping
  • Electrical pumping (correct)
  • Mechanical pumping
  • Optical pumping

    • What is a common application of lasers?

  • Medical imaging
  • Water purification
  • Generating electricity
  • Welding and cutting of materials (correct)

    • What is a type of laser that uses a solid-state gain medium?

    <p>Ruby laser</p> Signup and view all the answers

    What is a characteristic of flashtubes?

    <p>Producing extremely intense, incoherent, full-spectrum white light</p> Signup and view all the answers

    What is an advantage of He-Ne lasers over ruby lasers?

    <p>Longer operation duration</p> Signup and view all the answers

    What is a unique feature of laser beams?

    <p>High intensity</p> Signup and view all the answers

    What is another application of lasers besides welding and cutting?

    <p>Eye surgery</p> Signup and view all the answers

    What is the necessary condition for light amplification in lasers?

    <p>Population inversion</p> Signup and view all the answers

    Which of the following methods is used to obtain population inversion in Ruby lasers?

    <p>Optical pumping using Xenon flash lamp</p> Signup and view all the answers

    What type of laser uses a PN junction diode as the active medium?

    <p>Semiconductor laser</p> Signup and view all the answers

    What is the characteristic of lasers that maintain a population inversion indefinitely?

    <p>Continuous output</p> Signup and view all the answers

    Which type of laser uses macromolecules to produce different laser light from a single medium?

    <p>Dye laser</p> Signup and view all the answers

    What is the term for the delivery of energy to produce a population inversion?

    <p>Pumping</p> Signup and view all the answers

    Which of the following lasers is an example of a three-level laser?

    <p>Ruby laser</p> Signup and view all the answers

    What is the characteristic of lasers that have a short-lived population inversion?

    <p>Pulsed output</p> Signup and view all the answers

    What is the main principle for amplifying light in a Laser system?

    <p>Stimulated emission</p> Signup and view all the answers

    What is the condition for laser operation?

    <p>N1 &lt; N2</p> Signup and view all the answers

    What is the term for the state of the medium in which there are a larger number of atoms in the higher energy state as compared to the lower energy state?

    <p>Population inversion</p> Signup and view all the answers

    What is the characteristic of laser light that refers to the constant phase relationship between emitted photons?

    <p>Coherent</p> Signup and view all the answers

    Who is credited with the concept of stimulated emission?

    <p>Albert Einstein</p> Signup and view all the answers

    What is the term for the number of upward transitions due to absorption?

    <p>N1 P12</p> Signup and view all the answers

    What is the relation between the Einstein coefficients B12 and B21?

    <p>B12 = B21</p> Signup and view all the answers

    What is the purpose of the metastable state in a laser system?

    <p>To enhance the probability of population inversion</p> Signup and view all the answers

    What is the characteristic of laser light that refers to its high intensity?

    <p>Intense</p> Signup and view all the answers

    Who built the first laser using the concept of stimulated emission?

    <p>Theodore H. Maiman</p> Signup and view all the answers

    Study Notes

    Flashtubes

    • A flashtube is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations.
    • Made of a length of glass tubing with electrodes at either end.

    Drawbacks of Ruby Laser

    • Requires high pumping power.
    • Efficiency of ruby laser is small.
    • Laser output is not continuous, occurs in form of pulses of microsecond duration.

    Gas Lasers

    • Used for continuous laser beam.
    • Vapor metal ions are employed as active media.
    • Main advantage: exceptionally high monochromaticity, most pure spectrum, and high stability of frequency.
    • Output of gas lasers is moderate but inferior to that of crystal lasers.

    He-Ne Laser

    • First gaseous laser to be developed.
    • Developed in 1961 by Ali Javan and associates.
    • A four-level laser.
    • Emits a wavelength of 6328A.

    Comparison of Ruby and He-Ne Lasers

    • Ruby laser: solid-state laser, three-level laser, pulsed laser, optical pumping, coolant required, output power of 10kW, operation duration of a few hours.
    • He-Ne laser: gaseous laser, four-level laser, CW laser, electrical pumping, no coolant required, output power of 0.5 to 5mW, operation duration of ~10,000 hours.

    Applications of Lasers

    • Welding, cutting of materials.
    • Eye surgery, treatment of dental decay, and skin diseases.
    • Barcode scanners in libraries and supermarkets.
    • Laser printers.
    • Nuclear Fusion.
    • CD/DVD players.
    • Holography.

    LASERS

    • Light Amplification by Stimulated Emission of Radiations.
    • Concept of Stimulated Emission given by Albert Einstein in 1917.
    • Charles H. Townes utilized the concept to build MASER in 1953.
    • Extension to optical region: Theodore H. Maiman built the first Laser in 1960.

    Properties of Laser Light

    • Monochromaticity: high degree of monochromaticity.
    • Coherent: all emitted photons bear a constant phase relationship with each other in both time and phase.
    • Directional: a very well-collimated beam that travels long distances with very little spread.
    • Intense: a very highly intense beam.

    Interaction of Radiation with Matter

    • Absorption: probability of absorption, B12 is the Einstein coefficient of absorption.
    • Spontaneous Emission: probability of spontaneous emission, A21 is the Einstein coefficient of spontaneous emission.
    • Stimulated Emission: probability of stimulated emission, B21 is the Einstein coefficient of stimulated emission.

    Relation Between Einstein Coefficients

    • In thermal equilibrium, total upward transition equals total downward transitions.
    • Substituting for probabilities, we get: A21 = B21 * B12 * N1 / N2.

    Principle of Laser Action

    • The main principle for amplifying light in a laser system is the stimulated emission.

    Concept of Population Inversion and Metastable States

    • State of the medium in which there are larger numbers of atoms in higher energy state as compared to the lower energy state.
    • The existence of metastable state enhances the probability of population inversion.

    Condition for Laser Operation

    • If N1 > N2, radiation is mostly absorbed, spontaneous radiation dominates.
    • If N2 >> N1, population inversion occurs, most electrons occupy level E2, weak absorption, stimulated emission prevails, and light is amplified.

    Population Inversion

    • Situation in which the number of electrons in the higher state exceeds that in the lower state (N2 > N1).
    • Methods to obtain population inversion: supply energy from outside, optical pumping, electrical pumping, chemical pumping, and laser pumping.

    Types of Lasers

    • Solid-state lasers: active medium is solid crystal (e.g., Ruby, Nd:YAG).
    • Gaseous lasers: active medium is gaseous (e.g., He-Ne, Co2).
    • Dye lasers: macromolecules used for different laser light from a single medium.
    • Semiconductor lasers: PN junction diode used for producing LASER.

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    Lecture Lasers PDF

    Description

    This quiz covers various types of lasers, including flashtubes, ruby lasers, and gas lasers, and their characteristics.

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