File Name: spontaneous and stimulated emission in laser .zip
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Stimulated emission , in laser action, the release of energy from an excited atom by artificial means. According to Albert Einstein , when more atoms occupy a higher energy state than a lower one under normal temperature equilibrium see population inversion , it is possible to force atoms to return to an unexcited state by stimulating them with the same energy as would be emitted naturally. In stimulated emission the emitted light wave will be coherent i.
Absorption, spontaneous emission, and stimulated emission are three related energy conversion processes. Chapter 6 discussed devices based on absorption including solar cells and photodetectors. Devices which operate based on spontaneous emission include LEDs and lamps. Optical ampliers and lasers operate based on stimulated emission. Absorption is the process in which optical energy is converted to internal energy of electrons, atoms, or molecules.
When an optical gain medium is pumped optically or electronically, an electron is pumped excited from a lower energy level to an upper energy level. This is how spontaneous emission and stimulated emission take place, and is schematically illustrated in Figure 1. Properties of photons generated by spontaneous and stimulated emission are quite different. Spontaneous emission takes place without interaction with other photons, and the direction and phase are random. Stimulated emission takes place when the excited electron interacts with another photon.
We have observed and quantified the gain compression effects on the modulation response of directly modulated DFB laser. The gain compression severely degrades the modulation response and is the limiting factor for achieving maximum modulation bandwidth. In this paper, the variation in modulation response with gain compression of spontaneous emission and stimulated emission is investigated by simulation. We have identified that damping from both stimulated and spontaneous emission contributes to the overall damping and the gain compression enhances both. It is shown that by modulating the spontaneous emission coupling ratio in a small cavity volume, the spontaneous emission rate increases via stimulated emission rate. The former enhances the modulation bandwidth.
Stimulated and spontaneous emission
We know that when an atom absorbs extra energy and goes in excited state. To return to its normal or ground state it emits the absorbed extra energy photon at an undetermined time. This unpredictable release of photon energy by an atom is called the spontaneous emission. Spontaneous emission occurs at random and the emission of atom has no relationship to any other atom. The stimulated emission occurs when a photon with the correct wavelength approaches to an excited atom.
The spontaneous and stimulated emission spectral functions are calculated using a band model consisting of the self-consistent densities of states calculated in a previous paper and an optical model with an energy-dependent matrix element and no selection rule for the radiative recombinations. The energy dependence of the matrix element is that for a transition from a parobolic conduction band to an acceptor level and should be a suitable one, because of a small conduction band tail and the occupancy of most of the holes in the vicinity of the acceptor ionization energy. General properties, such as the spontaneous emission band shape, the gain-current relationship, and the temperature dependence of current required to maintain a given gain are compared with those calculated without band tails and with band tails given by Kane's model. Considerable differences are found among various models and these are discussed. Detailed comparison with experimental data is made and good quantitative agreement is obtained in both cases, giving strong support to our conclusions concerning the band-tail structure.
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Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron or other excited molecular state , causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase , frequency , polarization , and direction of travel that are all identical to the photons of the incident wave. This is in contrast to spontaneous emission , which occurs at random intervals without regard to the ambient electromagnetic field.
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