Photon emission from solids

Laser excitation causes characteristic photon emissions from the solid phase, identifying polymorphic form and transformation rates. This technique is only suitable for non-fluorescing materials... 

The imaging of photon emission from the ROS/hydrogen donor/mediator system was applied to solid-type samples. We studied the photon emission of several foods. Hydrogen donor emission (Y emission) was observed from polyphenol rich vegetables and fruits (tea and banana), fermented foods (oyster sauce, soy sauce and miso), alcohol (wine, sake and beer), spices and cereals (wheat and rice). Mediator emission (Z emission) was seen from some vegetables (Japanese radish, Chinese yam and nozawa-na) and fruits (melon), egg white, meat and fish meat. Imaging detection has a potential for visualization of Y and Z component distribution through the Y and Z emission... 

Summary. This Chapter focuses on the investigation of fast electron transport studies in solids irradiated at relativistic laser intensities. Experimental techniques based upon space-resolved spectroscopy are presented in view of their application to both ultrashort Ka X-ray sources and fast ignition studies. Spectroscopy based upon single-photon detection is unveiled as a complementary diagnostic technique, alternative to well established techniques based upon bent crystals. Application of this technique to the study of X-ray fluorescence emission from fast electron propagation in multilayer targets is reported and explored as an example case. 

The details of the scintillation process are complicated and depend very much on the molecular structure of the scintillator. In organic crystals, the molecules of the organic solid are excited from their ground states to their electronic excited states (see Fig. 18.18). The decay of these states by the emission of photons occurs in about 10-8 s (fluorescence). Some of the initial energy absorbed by the molecule is dissipated as lattice vibrations before or after the decay by photon emission. As a result, the crystal will generally transmit its own fluorescent radiation without absorption. 

Photoemission — Photoemission is the effect first discovered by H. R. Hertz (1857-1894) in Karlsruhe and W. Hallwachs (1859-1922) in Dresden in 1887, which is now known to be the emission of electrons from solids under illumination by electromagnetic radiation. The significance of the phenomenon historically is that it gave the first clear indication that the photons postulated by -> Planck to explain the energy distribution of light emitted from a black body had a real physical existence. -> Einstein was able to show that the energy of electrons emitted by the solid should obey the law = hi/-o,... 

Excited electronic states thus give rise to photon emission with a yield smaller than unity on the other hand, absorption of these photons produces, in turn, excited electronic states, also with a yield smaller than unity. Consequently, if one neglects the possibility for the photons to escape from the solid, a quasi-equilibrium is established between these two forms of energy between which the near totality of the incident energy is recovered. However, every conversion from one form to the other is accompanied by a release of thermal energy. If the irradiated system does not use the energy in either of these forms for certain definite purposes, such as chemical reaction for instance, the totality of this energy will be finally converted into heat. 

The relationship between the weight concentration of the element to be analysed and the intensity measured from one of its characteristic spectral lines is a complex one. For trace analysis several mathematical models have been developed to correlate fluorescence to the atomic concentration. A series of corrections must be introduced to account for inter-element interactions, preferential excitation, self-absorption and the fluorescence yield (the heavier atoms relax by internal conversion without photon emission). All of these factors require the reference samples to be practically the same structure and atomic composition than the sample under investigation, for all of the elements present. It is mostly because of these reasons that quantitative analysis by X-ray fluorescence is difficult to obtain. When operating upon a solid sample, a perfectly clean surface is important, preferably polished, since the analysis concerns the composition immediately close to the surface. 

The spectrum of the excitations is shown in Fig. 10.5 for 2 A = 80 meV. The dashed lines show the uncoupled molecular excitons and photons, and the solid lines show the coherent part of the spectrum with well-defined wavevector. The crosses show the end-points of the spectrum of excitations for which q is a good quantum number. The spectrum of incoherent (weakly coupled to light) states is shown by a broadened line centered at the energy Eq. It follows from the expression for the dielectric tensor that this spectrum is the same as the spectrum of out-of-cavity organics. The spectrum of absorption as well as the dielectric tensor depend on temperature. This means that in the calculation of the temperature dependence of the polariton spectrum we have to use the temperature dependence of the resonance frequency Eo as well as the temperature dependence of 7 determining the width of the absorption maximum. However, the spectrum of emission of local states which pump polariton states can be different from the spectrum of absorption. The Stokes shift in many cases... 

---