Thermal photons

While the T — 0 limit has been taken formally, it should be noted that the electronic fluctuation correlations at room temperature are essentially equivalent to those at T = 0 for normal, nondegenerate systems. (Thermal photons at room temperature are generally unable to excite electronic transitions )... 

Neon fusion takes over when the temperature reaches 1 billion K. At this temperature, thermal photons have enough energy to knock fragments off neon nuclei in the form of helium ... 

In the case of silicon fusion, which begins at around 2 billion K, the reactions proceed in a slightly different manner and we return to a fusion scheme similar to that of neon. At this temperature, silicon nuclei are gradually gnawed down by thermal photons which detach helium nuclei, protons and neutrons from them. These light nuclei combine with intact silicon to give nuclei in the region of iron. Schematically,... 

The unused thermal photons which are not required in semiconductor photodri-ven charge generation, can contribute to heating water to facilitate electrolysis at an elevated temperature. The characteristics of one, two, or three series interconnected... 

K. Reemission of thermal photons is very efficient so that even the hottest molecules are cooled to below 3000 K before they cross the first interferometer grating 7.2 cm downstream of the heating stage. 

The essence of the experiment is now to measure the variation of the interference fringe visibility. Fig. 11 clearly shows a non-trivial monotonic decrease of the interference contrast with increasing laser heating power. This is the unambiguous signature of decoherence which we attribute to the enhanced probability for the emission of thermal photons that carry which-path information. 

Note that the above considerations concern only thermonuclear modes of p-nuclide synthesis. Some non-thermonuclear scenarios have in fact been proposed, like production by spallation reactions in the interstellar medium [71,72], or photonuclear reactions triggered by non-thermalized photons [73]. These models suffer from either too low efficiencies, or from constraints that limit their astro-physical plausibility. They are not discussed further here. 

The one-atom maser can be used to investigate the statistical properties of non-classical light [1298, 1299]. If the cavity resonator is cooled down to T < 0.5 K, the number of thermal photons becomes very small and can be neglected. The number of photons induced by the atomic fluorescence can be measured via the fluctuations in the number of atoms leaving the cavity in the lower level n — 1). It turns out that the statistical distribution does not follow Poisson statistics, as in the output of a laser with many photons per mode, but shows a sub-Poisson distribution with photon number fluctuations 70 % below the vacuum-state limit [1300]. In cavities with low losses, pure photon number states of the radiation field (Fock states) can be observed (Fig. 9.77) [1301], with photon lifetimes as high as 0.2 s At very low... 

The crosses on the T = 3 K curve are obtained in the experiment. For these measurements the cavity temperature was raised to 3 K in order to have more thermal photons (2.5) in the cavity. The agreement between theory and experiment is excellent. 

We should remark that, in order to observe genuine spontaneous effects in these single atom cavity experiments it is important to control the blackbody field and to reduce the number of thermal photons in the mode well below unity (k3X/h uigf < I), which requires very low temperatures. If this condition is not fulfilled, one observes the oscillations of the atomic system in the random thermal field, which also present interesting features. A discussion of these effects, along with the effect of quantum collapse and revivals of Rabi nutation in an applied coherent field can be found in re-... 

Example 9.1 At a temperature T, the average energy hv of a thermal photon is roughly equal to kT. As discussed in Chapter 2, at high temperatures electron-positron pairs will be spontaneously produced when the energy of photons is larger the than the rest energy 2mc of an electron-positron pair (where m is the mass of the electron). Calculate the temperature at which electron-positron pair production occurs. 

From the particle viewpoint, thermal radiation consists of photons which we shall refer to as thermal photons. Unlike in an ideal gas, the total number of thermal photons is not conserved during isothermal changes of volume. The change in the total energy, U = uV, due to the flow of thermal photons from or to the heat reservoir must be interpreted as a flow of heat. Thus, for thermal... 

With the above observations that the chemical potential of thermal radiation is zero, the interaction of a two-level atom with blackbody radiation (which Einstein used to obtain the ratio of the rates of spontaneous and stimulated radiation) can be analyzed in a somewhat different light. If A and A are the two states of the atom, and y is a thermal photon, then the spontaneous and stimulated emission of radiation can be written as... 

When we consider interconversion of particles and radiation, as in the case of particle-antiparticle pair creation and annihilation, the chemical potential of thermal photons becomes more significant (Fig. 11.4). Consider thermal photons in equilibrium with electron-positron pairs ... 

For reasons of symmetry we may assert that (ie+ = Pg-. Since = 0 we must conclude that for particle-antiparticle pairs that can be created by thermal photons Pe = Pe- = 0. 

Figure 11.4 Creation of particle-antiparticle pairs by thermal photons...

For an optical refrigerator, the photon occupation number n in the entropy flux rate (Eq. 16) has contributions from both the fluorescent photons of the refrigerator, rif v), and the ambient thermal photons, a(v). The latter is given... 

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