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Laser Resonator
Published in Andrei Khrennikov, Social Laser, 2020
In laser physics, one of the main problems in creating laser is approaching population inversion. However, population inversion is not enough to generate a laser effect. Stimulated and spontaneous emissions are compete with each other. Thus, before becoming an amplifying device, a gain medium pumped by an external energy source is first radiated as a usual electric “lamp.” Here, spontaneous emission is dominating. The light power is distributed over a variety of frequencies and directions of propagation, generally uniformly distributed. It is the optical cavity, the laser resonator, that creates the conditions necessary for stimulated emission to become predominant over spontaneous emission. The cavity or resonator is composed of two mirrors (Fig. 3.1) that bounce the beam back and forth through the gain medium. One of the mirrors is only partially reflecting (the left-hand side mirror) and another is totally reflecting (the right-hand side mirror).
Basic Processes of Interaction of Radiation with Matter
Published in Mikhail G. Brik, Chong-Geng Ma, Theoretical Spectroscopy of Transition Metal and Rare Earth Ions, 2019
Mikhail G. Brik, Chong-Geng Ma
Finally, under some special circumstances, the absorption coefficient in Eq. (2.67) can become negative, which implies that g1n2 >> g2n1. This will be realized when a considerable part of atoms has been already excited before the sample is irradiated. Then α < 0 (negative absorption), and a remarkable situation is realized: The intensity of radiation is increased after passing through the sample. This happens because the number of the induced emission transition significantly exceeds the number of induced absorption transition. The state of a system, when the number of atoms at the upper energy level is greater than at the lower level, is called the population inversion. Creating population inversion is necessary for laser performance.
Transients and Instabilities in FIR Lasers
Published in Peter K. Cheo, Handbook of Molecular Lasers, 2018
Pierre Glorieux, Didier Dangoisse
In order to generate a population inversion between levels 2 and 3, a strong infrared (IR) radiation resonant or quasi-resonant with levels 1 and 2 is coupled to the medium. Practically, the population inversion is created by optical pumping with an infrared laser. In a FIR laser with longitudinal pumping, there is a velocity selection through optical pumping because only one velocity group is in resonance with the pump radiation and only a very narrow velocity group is transferred to the excited vibrational state. Moreover, if the IR radiation is exactly on resonance with the IR transition, the particular velocity group which is pumped is that with a zero component along the field direction, so there is no Doppler shift. In very particular conditions, Doppler broadening and shift are responsible for new features, which will be described later.
Counter rotating terms and dipole–dipole interaction effects on the entanglement and population inversion of two qubits interacting with a two-mode field
Published in Journal of Modern Optics, 2021
F. Jahanbakhsh, M. K. Tavassoly
The atomic population inversion gives some information about the rate of energy exchange between atoms and field, that is the basis of laser performance. This phenomenon, originates from the quantum interference in phase space, can be observed in experiment, using the state control of atomic beam leaving the cavity by ionization detectors [81,82]. This quantity for two-level atoms indicates the difference between their upper- and lower-level populations. Therefore, the atomic population inversion for ‘atom 1+atom 2’ in our desired system is defined as follows using reduced density matrixes in the Equations (13) and (14): where is known as the atomic inversion operator. It can be readily found that .
Light, the universe and everything – 12 Herculean tasks for quantum cowboys and black diamond skiers
Published in Journal of Modern Optics, 2018
Girish Agarwal, Roland E. Allen, Iva Bezděková, Robert W. Boyd, Goong Chen, Ronald Hanson, Dean L. Hawthorne, Philip Hemmer, Moochan B. Kim, Olga Kocharovskaya, David M. Lee, Sebastian K. Lidström, Suzy Lidström, Harald Losert, Helmut Maier, John W. Neuberger, Miles J. Padgett, Mark Raizen, Surjeet Rajendran, Ernst Rasel, Wolfgang P. Schleich, Marlan O. Scully, Gavriil Shchedrin, Gennady Shvets, Alexei V. Sokolov, Anatoly Svidzinsky, Ronald L. Walsworth, Rainer Weiss, Frank Wilczek, Alan E. Willner, Eli Yablonovitch, Nikolay Zheludev
To appreciate the difficulties, it is necessary to recall that light amplification by stimulated emission of radiation (LASER) requires prevalence of the stimulated emission over the stimulated absorption, which implies a higher population of an upper energy state over a lower energy one: , i.e. a population inversion at the corresponding lasing transition. The latter condition requires an incoherent pump with a rate higher than a decay rate of the upper state. In the case of pumping by incoherent radiation, this condition requires a sufficiently large flux P of incoherent photons, , where is a resonant cross section of the field–matter interaction and the lifetime of the upper state. The resonant cross section and the lifetime decrease proportionally to the square and the cube of the wavelength λ, respectively, resulting in a rapid increase in the required pumping flux P ~ λ−5. The existing sources of incoherent radiation in the high frequency ranges, such as X-ray tubes, LINACs and synchrotrons simply cannot provide the required flux. Besides, population inversion alone is not yet a sufficient condition for lasing. Indeed, the amplification requires a prevalence of a net resonant gain G over the off-resonant losses caused by the photoionization and Compton scattering, β, that is , where the net resonant gain is defined as