Spontaneous emission signal

The perturbative evaluation of the TFG spontaneous emission signal follows similar lines. Starting from Eq. (13), using the approximation (16), calculating P(t) to first order in the pump field, and retaining only sequential contributions in the RWA, one arrives at the result ... 

The first term in Eq. (4.3) is reminiscent of Eq. (3.2) for the spontaneous emission spectrum. It represents a doorway wavepacket created by the pump in the excited state, which is then detected by its overlap with a window. The only difference is that the role of the gate in determining the window in SLE is now played by the probe Wigner function W2. In addition, the pump-probe signal contains a second term that does not show up in fluorescence. This term represents a wavepacket created in the ground state (a hole ) that evolves in time as well and is finally determined by a different window Wg [24]. In the snapshot limit, defined in the preceding section, we have... 

If now an input signal of die resonant frequency is fed into the cavils, il can bring about spontaneous emission, and amplification will occur. The shortcoming ol this arrangement is that Ihe ammonia resonance cannot lie tuned and il represents an impracticably narrow bandwidth. On Ihe other hand, like any other amplifier, it cun he made fit oscillate, so that it can be used as a very stable frequency standard (ammonia clock). 

Collisional de-excitation is called quenching because it competes with spontaneous emission, and if significant the fluorescent signal will be reduced, or quenched. Chemical decay can also be important in some circumstances. 

The fluorescence technique, like other methods based on scatter (elastic or inelastic), has been shown by us - and others to be a reliable unperturbing method of measuring spatial/ temporal flame temperatures and species concentrations. To avoid the dependency of the fluorescence signal on the environment of the emitting species, it has been shown by several workers that optical saturation of the fluorescence process (i.e., the condition occurring when the photoinduced rates of absorption and emission dominate over the spontaneous emission and colli sional quenching rates) is necessary. Pulsed dye lasers have sufficient spectral irradiances to saturate many transitions. Our work has so far been concerned with atomic transitions of probes (such as In, Pb, or T1) asoirated into combustion flames and plasmas. 

P+ and P are the probabilities for absorption and emission, respectively B+ and B are the coefficients of absorption and of induced emission, respectively A- is the coefficient of spontaneous emission and p v) is the density of radiation at the frequency that induces the transition. Einstein showed that B+ = B, while A frequency dependence, spontaneous emission (fluorescence), which usually dominates in the visible region of the spectrum, is an extremely improbable process in the rf region and may be disregarded. Thus the net probability of absorption of rf energy, which is proportional to the strength of the NMR signal, is... 

The three incoming fields j = 1,2,3 will be treated classically. For these fields, E/t) is a classical function of time representing their temporal envelopes. The generated signal field 4 = s will be treated quantum mechanically, since it is generated by spontaneous emission. For that field, we have62... 

Regardless of the size of the laser, one always has to start with an active medium, which is energized, or pumped, by either flash lamps or another laser. This creates an inversion, which is then extracted by amplification of an externally applied laser signal or spontaneous emission. This process takes place in a resonator cavity that consists of two or more mirrors, and which may contain optical switches as well. Such an assembly is referred to as an... 

An architecture very closely related to the cavity-dumped oscillator is the regenerative amplifier. The principle difference is that the laser oscillation in a regenerative amplifier does not build up from spontaneous emission, but is initiated by a signal injected into the resonator fi om the outside, as the Pockels cell is switched to transmission. This injected signal is then trapped in the cavity and amplified until it has reached maximum intensity, at which point it is ejected (dumped) from the cavity. 

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