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4124 results in Optics, Optoelectronics and Photonics

Page 24 of 207

A First Course in Laboratory Optics
  • Andri M. Gretarsson
  • Published online:
    20 May 2021
    Print publication:
    03 June 2021
  • An optics experiment is the product of intricate planning and imagination, best learned through practice. Bringing forth the creative side of experimental physics through optics, this book introduces its readers to the fundamentals of optical design through seven key experiments. The book includes several topics to support readers preparing to enter industrial or academic research laboratories. Optical sources, model testing and fitting, noise, geometric optics, optical processes such as diffraction, interference, polarization, and optical cavities, are just some of the key topics included. Coding tutorials are provided in the book and online to further develop readers' experience with design and experimental analysis. This guide is an invaluable introduction to the creative and explorative world of laboratory optics.

  • 1 - Absorption Spectroscopy of Gases

  • George Stewart, University of Strathclyde
  • Book:
    Laser and Fiber Optic Gas Absorption Spectroscopy
    Published online:
    07 April 2021
    Print publication:
    08 April 2021, pp 1-20

  • Summary

    The fundamental description of the absorption of light by a gas through the Beer-Lambert law is introduced with the definitions given of the important parameters, such as line-strength, absorption cross-section and absorption coefficient. Broadening of gas absorption lines from Doppler effects and molecular collisions is explained in detail and the consequent absorption line-shape functions are presented in the form of Gaussian, Lorentzian or Voigt profiles. The extraction of information on the gas concentration, pressure or temperature from a measured line-shape is discussed, along with the practical issues and limitations. The origin and nature of the absorption lines arising from the excitation of rotational and vibrational states of gas molecules is reviewed with a particular interest in the overtone lines in the near-IR region. Examples of near-IR absorption lines from the HITRAN database for carbon monoxide, carbon dioxide, acetylene, methane, water, ammonia and hydrogen sulfide are presented so that the optical attenuation may be calculated in the design of a practical gas sensor system.

  • 8 - Mid-IR Systems and the Future of Gas Absorption Spectroscopy

  • George Stewart, University of Strathclyde
  • Book:
    Laser and Fiber Optic Gas Absorption Spectroscopy
    Published online:
    07 April 2021
    Print publication:
    08 April 2021, pp 232-254

  • Summary

    The state-of-the-art of mid-IR laser absorption spectroscopy is reviewed to take advantage of the stronger absorption lines. The properties of mid-IR diode lasers are discussed, including quantum well, inter-band cascade and quantum cascade lasers for gas sensing at wavelengths beyond two microns. As an alternative to diode lasers, mid-IR laser sources based on down-conversion from the near-IR are reviewed using either difference frequency generation or optical parametric oscillation and examples are given of their design as tuneable mid-IR CW sources or as mid-IR frequency combs. Examples of compact mid-IR laser combs formed from micro-resonators in silicon are also discussed. The important spectroscopic techniques of wavelength modulation spectroscopy, cavity-enhanced, evanescent-wave and dual-comb spectroscopy are all discussed in the context of the mid-IR with examples of the performance that can be attained. The performance and limitations of the most common mid-IR transmitting fibres and mid-IR detectors are also reviewed. Finally a comparison is given of the relative merits of gas absorption spectroscopy in the near-IR and mid-IR and where each has an important role to play.

Page 24 of 207