Scattering Thomson

Schoenlein R W, Leeman W P, Chin A H, Volfbein P, Glover T E, Balling P, Zolotorev M, Kim K-J, Chattopadhayay S and Shank C V 1996 Femtosecond x-ray pulses at 0.4 A generated by 90° Thomson scattering a tool for probing the structural dynamics of materials Science 274 236-8... 

One of the first proposed processes for obtaining electromagnetic radiation up to the X/y-ray range using laser beams was the Thomson scattering (see e.g., [88] and references therein). As it is known, this is the scattering of... 

From an experimental viewpoint, Thomson scattering has been recently observed by using electron beams from a LIN AC [91] as well as from a laser-plasma source based on LWFA [92]. This latter observation, in particular, allows the availability of table-top, tunable sources of X/7-rays to be foreseen. 

Teramobile, 112 Thomson scattering, 168, 179 Three-level system, 11 Three-step model, 65 Time-resolved second harmonic generation, 29 TOF spectroscopy, 5 Transient depletion field screening (TDFS), 28... 

For a 1 the scattered light spectrum is gaussian with a width determined by the electron temperature, because it is due to the incoherent sum of Thomson scattering from individual, thermally moving electrons. The intensity and spectral linewidth of scattered light therefore yield electron density and temperature. 

Elastic Scattering (Thomson Scattering) Non-Elastic Scattering (Compton Scattering)... 

Finally we must deal with perturbations not to pressureless matter but to baryons and photons. At early times, the universe is radiation dominated, and pr = p/3 for radiation. Before the epoch of recombination, the same Thomson scattering processes that keep the baryons ionized also keep the radiation tightly-coupled to the ions. The nuclei have pressure pb = (5kT/dmp)p [Pg.182]

The collision term, C[f] is the rate for interactions to change /(k. p. rj). For photons, this is from Thomson scattering off of electrons, with differential cross section... 

Thomson scattering radiation is produced as the electron oscillates in the laser field (we define the laser strength parameter as a0 = =... 

Fig. 11.1. Principle of the nonlinear Thomson scattering X-ray source. The nonlinear motion of the free plasma electrons oscillating in the strong electromagnetic laser held (ao) produces high harmonics of the fundamental laser light that can reach the X-ray spectral range. As ao is increased, the radiation becomes more collimated...

Fig. 11.4. Energy distribution functions of the radiation produced by nonlinear Thomson scattering in a laser field for two laser intensities. Radiation above 1 keV can be achieved for laser intensities larger than 1020 W/cm2...

Fig. 11.7. X-ray intensity as a function of the electronic density of the plasma and the laser strength parameter. The process of nonlinear Thomson scattering for the production of X-ray emission can be observed for the highest laser intensities and along the laser axis (ao = 5.6 for the two first figures)...

Nonlinear Thomson scattering can only be observed for the highest laser intensities, as shown in Fig. 11.7. As expected from the theory, when ao < 1, the nonlinear Thomson scattering vanishes and the collisional radiative processes from the thermal plasma prevail (Bremsstrahlung and radiative recombination). For ao > 1, these latter processes are still effective, as shown by the quadratic dependency on the electronic density of the plasma observed for 9 = 40°. However, this isotropic thermal emission remains less intense than the collimated nonlinear Thomson scattering emission and becomes detectable only at a large angle of observation (> 40°). 

The derivation of Thomson scattering from first principles is a bit involved. Given an electron of charge e with velocity v = cfl t) at the source point x t), where c is the speed of light in vacuum, the scalar and vector potentials field point r(f), are given by the Lienard94 -Wiechert95 expressions ... 

The scattering of X rays by matter consists of two processes. The first process is the classical incoherent scattering, with no change in wavelength, called Thomson scattering, where the average intensity (S) of plane-polarized radiation, due to an electric field E, incident on a single electron is... 

The X rays, which are produced with lack of phase coherence with intensity I0, if they impinge on a stationary electron at the origin, scatter (Thomson scattering) with intensity I at a distance R from the electron, at an angle 8 from the direction of the incoming beam as follows ... 

Here the Thomson scattering cross section per electron cr0 = (e4/87t o n2c4) = 0.665 barns seems awfully small, but remember that there are about 1026 electrons m 3 in a typical crystal The polarization factor (in square brackets) is a maximum at 0 = 90° (complete polarization). 

During the last 25 years X-ray spectroscopy has been intensively developed for plasma diagnostics. Since the first application of X-ray spectrometers on the early fusion devices such as PLT and TFR, it has been used to determine basic plasma parameters such as the temperature of ions and electrons. It is now frequently being applied not only to low density plasmas in tokamaks and astrophysical objects [1], but also to laser-produced plasma [2]. It has been shown, that the precision of plasma parameters as obtained from X-ray spectroscopy is competitive to the standard methods for plasma diagnostics, such as Thomson scattering and charge exchange spectroscopy for electron and ion temperature, respectively [3]. 

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