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Spontaneous emission losses

E, 1+) states (localized to the left of the potential barrier) to a wave packet of E, 2 ) states (localized to the right of the barrier), while keeping the population 1 of the [ ) states to a bare minimum. The latter serves to minimize spontaneous, emission losses. ... [Pg.264]

As mentioned above, by keeping the population of the intermediate resonance low (as is the case in Fig. 11,10), the spontaneous emission losses are effectively i eliminated. Figure 11.11 shows the intermediate level population as a function of four different pulse intensities. The reaction probability for all plotted intensities isj near unity. However, it is evident that the intermediate state population throughout the process decreases with increasing pulse intensity. Thus, to avoid spontaneails j emission losses, high pulse intensities should be used. i ... [Pg.264]

However, it is possible to concentrate most of the radiation onto a few modes in such a way that the number of photons in those modes becomes large and the stimulated emission in those modes will dominate (although the total spontaneous emission rate into all modes may still be larger than the induced rate in these few modes). Such selection of few modes is realized in a laser by using an appropriate resonator, which should exhibit a strong feedback for those modes. The resonator will allow an intense radiation field to be built in the modes with low losses, and will prevent oscillation from being reached in the modes with high losses. [Pg.52]

Since 1946, when it was first proposed that the spontaneous emission from an excited state of an emitter can be significantly altered if it is placed into low-loss wavelength-scale cavity (Purcell, 1946), various microresonator designs for efficient control of spontaneous emission have been explored... [Pg.54]

Laser oscillation will start if N can be increased to a certain value Nc> called the critical inversion. Nc depends upon the spontaneous emission coefficient and the losses in the laser cavity. [Pg.229]

The first term on the right-hand side is a gain term due to transitions between level m and n, the second a loss term Nn is the number of atoms in level n. The important new element introduced by Einstein was the discovery of spontaneous emission. The transition probability is the sum of two contributions ... [Pg.13]

Thus far we have dealt with the idealized case of isolated molecules that are neither -subject to external collisions nor display spontaneous emission. Further, we have V assumed that the molecule is initially in a pure state (i.e., described by a wave function) and that the externally imposed electric field is coherent, that is, that the " j field is described by a well-defined function of time [e.g., Eq. (1.35)]. Under these. circumstances the molecule is in a pure state before and after laser excitation and S remains so throughout its evolution. However, if the molecule is initially in a mixed4> state (e.g., due to prior collisional relaxation), or if the incident radiation field is notlf fully coherent (e.g., due to random fluctuations of the laser phase or of the laser amplitude), or if collisions cause the loss of quantum phase after excitation, then J phase information is degraded, interference phenomena are muted, and laser controi. is jeopardized. < f... [Pg.92]

In addition to absorption and stimulated emission, a third process, spontaneous emission, is required in the theory of radiation. In this process, an excited species may lose energy in the absence of a radiation field to reach a lower energy state. Spontaneous emission is a random process, and the rate of loss of excited species by spontaneous emission (from a statistically large number of excited species) is kinetically first-order. A first-order rate constant may therefore be used to describe the intensity of spontaneous emission this constant is the Einstein A factor, Ami, which corresponds for the spontaneous process to the second-order B constant of the induced processes. The rate of spontaneous emission is equal to Aminm, and intensities of spontaneous emission can be used to calculate nm if Am is known. Most of the emission phenomena with which we are concerned in photochemistry—fluorescence, phosphorescence, and chemiluminescence—are spontaneous, and the descriptive adjective will be dropped henceforth. Where emission is stimulated, the fact will be stated. [Pg.16]

Here ofw = fi)j j(v is the flip operator of the jth atom and the vacuum Rabi-firequency g is assumed to be equal for all atoms. All spatial phases have been absorbed in the definition of the atomic states. We have introduced an imaginary part to the Hamiltonian to take into account losses from the excited states, e.g., via spontaneous emission. The model does not take into account however relaxation from the excited states back into the lower levels. [Pg.212]

Here G is the gain coefficient for stimulated emission, k is the decay rate due to loss of photons by mirror transmission, scattering, etc., f is the decay rate for spontaneous emission, and p is the pump strength. All parameters are positive, except p, which can have either sign. [Pg.81]

During spreading, spontaneous emissions of herbicides to the atmosphere can reach 30% of the applied dose, and they depend on several factors such as meteorological conditions and spread droplet size. A study pointed out the importance of not using droplets with a size below 100 /rm to avoid their dispersion from the spreading point (730). Taylor and Spencer" showed that losses of... [Pg.981]


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Spontaneous emission

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