Laser Physics | Its Principles | Important Types

LASER PHYSICS

What is laser physics?

Laser physics or laser science is a subdivision of optics that deals with the theory, working, construction, and practice of lasers. In exact terms, laser physics is associated with optical cavity design, the temporal development of the light field (in laser), quantum electronics, non-linear optics, construction of laser, and the physics behind generating a population inversion in laser media, laser beam propagation.

Who laid the foundation of laser physics?

  • In 1917, Sir Albert Einstein laid the foundation of a laser by re-deriving Max Planck’s radiation law. Albert Einstein formalized probability coefficients on absorption, stimulated emission, and spontaneous emission of electromagnetic radiation.
  • In the year 1928, Rudolf W. Ladenburg set the existence of stimulated emission and Valentin A. Fabrikant made the first proposal for laser (light amplification by stimulated emission of radiation) and stated the conditions needed for amplifying light with stimulated emission in 1939.
  • R. C. Retherford and Willis E. Lamb observed and demonstrated stimulated emission in hydrogen spectra in 1947.
  • In 1952, Alexander Prokhorov and Nikolay Basov described the theoretical principles behind the operation of a maser or microwave laser (Prokhorov and Basov were awarded a Nobel Prize for their research in the field of laser physics).
  • In 1960, Theodore Maiman built the first working ruby-pulse laser at the Hughes Research Laboratories.

What is the basic working principle of a laser?

Electrons residing in a lower energy level possess a tendency to absorb light energy externally in the form of photons or phonons for reaching the higher energy level and energy in the absorbed photon or phonon is equal to the difference of energy between the two levels. In the case of light energy, this means that certain atoms can absorb only a specific wavelength of light for a transition.

After reaching the excited higher state, an electron cannot stay there forever. Electrons tend to decay to a lower energy level by losing energy. This transition of electrons generally occurs at different time intervals and emits energy in the form of photons. This entire process of electron transition without any external interference is termed spontaneous emission. In this, the emitted electron has a random direction and phase.

At times the electrons are subjected to external influence for transiting from a high-energy to a low-energy state. In this case, the photon emitted during the transition process matches the actual photon’s direction, phase angle, and wavelength. This process of photon emission is termed stimulated emission that is used in lasers to know more about this topic click here.

Every laser is designed to have a gain medium, that amplifies the emitted photon beam, this gain medium is controlled in terms of size, concentration, purity, and shape and at a point after stimulated emission when the no. of electrons present in an excited energy level has become greater than the no. of electrons available in the lower energy level at that state and, a population inversion occurs and Here, the rate of stimulated photon emission exceeds the rate of energy absorption by the electrons. Therefore, the light or photons emitted get amplified. This process is called optical amplification.

What are the major types of lasers?

Gas Laser:

Gas lasers (like HeNe Laser or CO2 Laser) use gaseous compounds for coherent amplification of light. Gaseous discharges can be made to amplify different wavelengths of light. These lasers are widely used for research and commercial purposes. Carbon dioxide lasers produce high power continuous beam of infrared light having principal wavelength bands ranging from 9.6 to 10.6 micrometers. These lasers are highly power-efficient with output power to pump power ratio reaching as high as 20%.

laser physics
Wavelengths of commercially available lasers.
Image source: Danh (https://commons.wikimedia.org/wiki/File:Commercial laser lines.svg), „Commercial laser lines“, https://creativecommons.org/licenses/by-sa/3.0/legalcode (laser physics)

Excimer Laser:

Excimer lasers use ultraviolet light for producing microelectronic devices, semiconductor integrated circuits and micro-machines. Excimer lasers (also known as exciplex laser) are developed using noble gases like Argon, Krypton, or Xenon along with reactive halogen gas like fluorine or chlorine.

Chemical Laser:

Chemical lasers provide the energy for the excitation of electrons from chemical reactions. These lasers are capable of producing large amounts of energy in a short duration of time and are therefore used in high power lasers.

Solid-state Laser:

Solid-state lasers use a glass or crystalline rod that is doped with ions for enabling the electrons to reach the required energy levels. The dopant is responsible for maintaining population inversion. For example ruby laser.

Fiber Laser:

Optical fiber lasers use total internal reflection or TIR to transmit light rays with the help of optical fibers. These lasers find their application in transmitting light rays over long distances and in reducing the thermal distortion of the laser beam.

Photonic crystal Laser:

Photonic crystal Laser uses Nano-structures for providing mode confinement.

Semiconductor Laser:

Semiconductor Lasers use semiconductor diodes for electrically pumping. The recombination energy released is responsible for maintaining the optical gain.

Dye Laser:

Dye lasers have an organic dye functioning as the gain medium. These lasers can operate in different light wavelengths and can produce short-duration pulses.

Free-electron Laser:

Free-electron lasers provide the widest possible range for lasing action. These lasers generate high power coherent beams with radiations ranging from infrared to visible rays.

Laser sizes: Top (microscopic laser) Bottom (large glass laser) Image source: anonymous, Laser sizes, marked as public domain, more details on Wikimedia Commons(laser physics)

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About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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