What is a Laser?
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Questions and Answers

What is the energy of the emitted photon equivalent to?

  • The energy of the ground state of the atom or molecule
  • The energy of the excited state of the atom or molecule
  • The energy of the stimuating photon
  • The energy difference between the excited and ground states of the atom or molecule (correct)

    • What happens when an excited atom or molecule encounters a photon with an energy matching the energy difference between its current excited state and a lower energy state?

  • It stays in the excited state for a longer period
  • It emits a photon with a higher frequency
  • It is stimulated to return to the ground state immediately
  • It is induced to return to the lower energy state earlier than it otherwise might (correct)

    • What is the result of stimulated emission?

  • Two incoherent photons moving in opposite directions
  • Two coherent photons moving in the same direction (correct)
  • One photon with a lower frequency
  • One photon with a higher frequency

    • What is the necessary condition for laser action to occur?

    <p>The number of particles in the higher energy state is greater than the number in the lower energy state</p> Signup and view all the answers

    What is the term for the non-equilibrium situation in which the number of atoms in the higher energy state exceeds that in the lower energy state?

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

    What is the characteristic of a metastable state?

    <p>A relatively long lifetime</p> Signup and view all the answers

    How long can atoms stay in metastable states?

    <p>From 10^-6 to 10^-3 seconds</p> Signup and view all the answers

    How much longer do atoms stay in metastable states compared to excited states?

    <p>10^3 to 10^6 times longer</p> Signup and view all the answers

    What does the acronym 'laser' stand for?

    <p>Light Amplification by Stimulated Emission of Radiation</p> Signup and view all the answers

    What is a characteristic of laser light?

    <p>It is monochromatic</p> Signup and view all the answers

    What is the result of absorption of photons by atoms or molecules?

    <p>They are elevated to a higher energy state</p> Signup and view all the answers

    What is spontaneous emission?

    <p>The process of releasing photons</p> Signup and view all the answers

    What is the primary advantage of laser light's directionality?

    <p>It can be focused onto a very small spot</p> Signup and view all the answers

    What is the benefit of laser light's coherence?

    <p>It increases the brightness of the light</p> Signup and view all the answers

    What is the significance of polarization in laser light?

    <p>It is useful for various applications</p> Signup and view all the answers

    What is the primary interaction between radiation and matter in lasers?

    <p>Absorption, spontaneous emission, and refraction</p> Signup and view all the answers

    Study Notes

    What is a Laser?

    • Laser is an acronym for "Light Amplification by Stimulated Emission of Radiation"
    • A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation

    Properties of Laser

    • Monochromaticity: Laser light consists of light of a single wavelength (or color)
    • Coherence: Laser light is coherent, with two types of coherence:
      • Directionality: Lasers produce a highly collimated beam of light
      • Brightness: Lasers can achieve extremely high intensities and brightness, especially when focused
    • Polarization: Many lasers produce polarized light, with the oscillations of the light's electromagnetic field following a particular orientation

    Interaction of Radiation with Matter in Lasers

    • Absorption: Atoms or molecules absorb photons, elevating them to a higher energy state
    • Spontaneous Emission: Atoms or molecules return to their lower energy state, releasing a photon
    • Stimulated Emission: An excited atom or molecule is induced to return to a lower energy state, emitting a photon in phase with the stimulating photon

    Population Inversion

    • Under normal thermodynamic equilibrium conditions, the number of particles in a lower energy state is greater than the number in a higher energy state
    • For laser action to occur, this distribution needs to be inverted, with more particles in an excited (higher energy) state than in the ground (lower energy) state
    • Population inversion: The situation in which the number of atoms in the higher energy state exceeds that in the lower energy state (N2 > N1)

    Metastable State

    • A metastable state refers to an excited energy state of an atom or molecule with a relatively long lifetime
    • Atoms or molecules in metastable states can remain excited for much longer periods, from microseconds to milliseconds or even longer
    • Atoms can stay in metastable states for about 10-6 to 10-3 seconds, which is 103 to 106 times longer than the time of stay of an atom at the excited state

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    Description

    This quiz explains the definition and properties of a laser, including its monochromaticity and stimulated emission of radiation.

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