Abstract
The birth of lasers in 1960 has led to an unprecedented proliferation of research activity across the globe aimed at amplifying light in a wide variety of materials. It is no wonder that we have now practically countless lasers emitting coherent radiation covering a significant part of the electromagnetic spectrum. Chapter 10 presents a survey of a few specific laser systems. For this purpose, the lasers have been grouped in terms of the state of the active medium, viz., gas, liquid, and solid-state lasers, and the operation of a popular laser from each category has been described with a special emphasis on the underlying physics. The active medium of a gas laser can be atoms, ions, and molecules. Consequently, we choose He-Ne, argon ion, and CO2 lasers from these respective categories for this survey. While dye lasers represent the liquid laser, Nd-YAG and Ti-sapphire lasers have been chosen, respectively, as the discrete wavelength and continuously tunable lasers from the solid-state laser category. Other kinds of lasers, the workings of which are distinctly different and do not truly qualify to be grouped with the majority of conventional lasers but nevertheless stand pretty tall in the laser world, have been addressed separately in this chapter. They include free electron lasers, excimer lasers, chemical lasers, gas dynamic lasers, and fiber lasers.
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Notes
- 1.
Although the lasing medium is a gas here, this class of lasers will be described under a different heading as the way they work distinctly differs from the other kind of gas lasers.
- 2.
This also explains as to why atomic gas lasers predominantly emit in the visible and near infrared regions of the e-m spectrum.
- 3.
The electron rotating in an orbit intrinsically possesses an angular momentum, and further as it also spins about itself (akin to Earth’s rotation about the Sun and itself), it is also endowed a spin angular momentum as well. Like the electron’s energy, its angular momentum is also quantized. These effects cause the energy levels of the electrons in the various excited states to split into sublevels denoted by the orbital quantum number n, angular quantum number l, and its spin s. The readers may please refer to any textbook on modern physics in this context.
- 4.
Coherence length of a laser is a measure of its spectral purity and mathematically can be expressed as the inverse of the spectral width of the laser emission. Coherence length and its bearing on the performance of a laser will be elaborated in detail in volume II of this book.
- 5.
The research work of William Bell, inventor of ion lasers, led to the development of the first atomic clock used in the Apollo missions to the Moon. The atomic clock he made is now on display along with his handwritten notes in the Smithsonian Museum of American History.
- 6.
The singlet and triplet states of a system are categorized depending on the orientation of the spins of the electrons that make up the system. When spins of all the electrons are paired, the resulting quantum state is a singlet state, while the case of electrons with unpaired spins is characterized as a triplet state. In the case of a molecule, the ground state is usually a singlet state, while the excited state involving an excited electron can be both singlet and triplet.
- 7.
- 8.
The working of a diffraction grating, both in the Littrow and non-Littrow modes, has been described in Chap. 11, Sect. 11.3.6.3.2, in the context of tuning the emission of a CO2 laser.
- 9.
Unlike the gas and liquid lasers, a solid-state laser needs a host that would hold the light emitting active atoms firmly in place and would, at the same time, allow unrestricted passage of both the pump and emitted photons. It is well known that the fraction of the pump energy that is not converted into laser light is realized as heat and the host must have adequate thermal property to allow rapid conduction of this heat to its surface.
- 10.
Thermal lensing effect occurs because the refractive index of the host material depends on the temperature. The hotter center of the rod has higher r.i. compared to that at the edges. A medium with such a spatial inhomogeneity in r.i will focus a beam of light just like a normal convex lens.
- 11.
Mechanical stress develops as expansion of the hotter center of the rod is higher than at the edges.
- 12.
An acoustic phonon is a quantum of atomic lattice vibration that essentially represents a quantum of sound.
- 13.
An optical phonon is nothing but a photon that represents a quantum of light.
- 14.
Lorenz force, also called electromagnetic force, is the force experienced by a moving charge particle due to the presence of electric and magnetic fields.
- 15.
In 1865, James Clerk Maxwell (1831–1879), a Scottish physicist, combined the Gauss’s laws of electricity and magnetism, Faraday’s law, and Ampere’s law into four equations, aptly termed as a unified theory of electromagnetic phenomena. The most remarkable inference of Maxwell’s equations, recognized as among the most important in science, is that light is an electromagnetic wave which manifests as time varying magnetic and electric field propagating in space.
- 16.
Relativistic speed is the speed at which the relativistic effects become significant. Normally relativistic effects are accounted for when the speed of an object exceeds one-tenth of the speed of light.
- 17.
Lorentz factor is the measure of the change of the physical properties, such as length, and mass, of a moving body compared to the values at its stationary state.
- 18.
Relativistic Doppler effect, like its classical counterpart described in Chap. 8, is also a change in frequency of light caused by the relative motion between the source and observer but by taking into account the effects caused by the spatial theory of relativity.
- 19.
Directly follows from Heisenberg’s uncertainty relation
- 20.
Mani Lal Bhaumik was born in a poverty stricken Bengali family and narrowly escaped death in the 1942 Bengal famine when over three million Bengalis perished primarily out of starvation and malnutrition. His journey from a mud hut in an obscure Bengal village to the marble mansions of California is a genuine story of rags to riches, indeed a leaf straight out of a fairy tale. As a child, he walked barefoot every day to his village school and worked hard to top the high school examination and earned a scholarship to attend college in Calcutta where he acquired his first pair of shoes in life. His invention of excimer laser made possible the LASIK eye surgery that is now extremely popular across the globe and laid the road for him to walk to the pinnacle of fame. His book, Code Name God: The Spiritual Odyssey of a Man of Science, represents an endeavor toward bridging the divide between science and spirituality. The profound impact that this book has made on humanity is evident from its translation into over 100 languages!
- 21.
President Reagan, a vocal supporter of the SDI, advocated that “lasers in space” would be a tool to rid the world of nuclear weapons and did not rule out the possibility of eventually sharing it with erstwhile Soviet Union.
- 22.
The working of a CO2 laser has been described quite extensively in Chap. 11.
- 23.
The profound impact of all light fiber-optic communication, without the requirement of any intermediate conversion of light into electronic form and back to light again after amplification, on humanity will be elaborated in detail in V-II of this book.
- 24.
Nicknamed as the “father of fiber-optic communication,” Charles Kuen Kao (1933–2018) won the 2009 Nobel Prize in Physics for his pioneering work that laid the foundation for the development of nearly lossless fiber that exists today.
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Biswas, D.J. (2023). Different Types of Lasers. In: A Beginner’s Guide to Lasers and Their Applications, Part 1. Undergraduate Lecture Notes in Physics. Springer, Cham. https://doi.org/10.1007/978-3-031-24330-1_10
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