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Synchrotron Radiation and Free-Electron Lasers
Published in Volker Ziemann, ®, 2019
In Section 10.3 we assumed that electron current was modest and the amplitude of the radiation was assumed to stay approximately constant during the electron’s passage through the undulator. If, on the other hand, the peak current is very high and a large number of electrons are micro-bunched and start radiating coherently, the intensity of the radiation grows along the undulator. This, in turn, increases the energy modulation and the ensuing micro-bunching causes the radiation to grow even more. The process can become unstable and leads to an exponential growth of the radiation [77, 78]. Since the growth is initiated by the spontaneously emitted radiation in the undulator, it is called self-amplified spontaneous emission, or SASE.
X-ray Shutters
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Several X-ray FEL facilities shown in Figure 9.1 are opening up new doors for exciting scientific research. These facilities are currently in the construction phase, commissioning, operation phase, or upgrade phase. The European X-ray Free-Electron Laser Facility (European XFEL) is under construction in Hamburg and Schleswig-Holstein, Germany, second quarter of 2017 will be commissioning and user operation. This facility will generate extremely brilliant X-rays (peak brilliance = 1033 photons/s/mm2/0.1% BW) with ultrashort pulses up to 100 fs and with a repetition pulse rate at 4.5 MHz of spatially coherent X-rays with wavelengths down to 0.1 nm. The basic process to generate the X-ray pulses is self-amplified spontaneous emission (SASE), where electron bunches are generated by a high brightness gun, brought to high energy of up to 20 GeV (17.5 GeV is the energy foreseen for the standard mode of operation of the European XFEL facility) through a superconducting linear accelerator and passed through 200 m long undulators, where the X-ray pulses are generated. It will have 2700 pulses/train with a 100 ms repetition rate, as shown in Figure 9.4. For electron energy of 17.5 GeV with photon energy of 12.4 keV, it will have a peak power of 20 GW and an average power of 65 W. The design parameters of European XFEL front-end shutters are described in Sinn et al. (2012). Figure 9.5 shows the photon shutter which is installed in the European XFEL tunnel for SASE1 beamline, which was designed and build by Reuter GmbH Company. The main components of the shutter are a power absorber B4C (the B4C [boron carbide] melting point is 2300°C, but carbon segregation to the surface occurs at about 1400°C), a collimator, and a thick tungsten block. The beam comes from left incidence on the surface of the B4C at a 8° grazing incidence. The B4C has side cooling with copper tubes to absorb the heat load on the B4C. The absorber B4C can be moved in and out of the beam path by using a pneumatic cylinder.
Light, the universe and everything – 12 Herculean tasks for quantum cowboys and black diamond skiers
Published in Journal of Modern Optics, 2018
Girish Agarwal, Roland E. Allen, Iva Bezděková, Robert W. Boyd, Goong Chen, Ronald Hanson, Dean L. Hawthorne, Philip Hemmer, Moochan B. Kim, Olga Kocharovskaya, David M. Lee, Sebastian K. Lidström, Suzy Lidström, Harald Losert, Helmut Maier, John W. Neuberger, Miles J. Padgett, Mark Raizen, Surjeet Rajendran, Ernst Rasel, Wolfgang P. Schleich, Marlan O. Scully, Gavriil Shchedrin, Gennady Shvets, Alexei V. Sokolov, Anatoly Svidzinsky, Ronald L. Walsworth, Rainer Weiss, Frank Wilczek, Alan E. Willner, Eli Yablonovitch, Nikolay Zheludev
Here is a radiative linewidth of the resonant transition and is a total linewidth which includes an inhomogeneous broadening. In the case of poor radiative broadening, gain scales as G ~ λ2. Additional line broadening mechanisms reduce the gain by a factor , making it very difficult to overcome the off-resonant losses. Finally, the very fast (from pico- to femtosecond) decay rate of the high-frequency atomic transition and radiation damage of mirrors by the flux of high-energy photons, as well as an absence of high finesse cavities in the high-frequency range, make a single-pass self-amplified spontaneous emission (SASE) regime a necessity, leading to an additional rather stringent requirement. Namely, the single-pass net gain should be reasonably high, , where L is the length of an amplifying medium.
Quantum theory for 1D X-ray free electron laser
Published in Journal of Modern Optics, 2018
The ratio of photon energy to FEL bandwidth was first identified by Smetanin in Ref. [9] as the quantity defining the applicability limit for the classical X-ray FEL theory. The quantum theory of self-amplified spontaneous emission (SASE) FEL was later predicted by Bonifacio et al. in Ref. [10]. Yet, the question ‘What defines the quantum regime of the free-electron laser’ has been raised again recently [11]. In order to facilitate the transition from classical to quantum FEL theory, one needs to relate the classical approach to the quantum one using the same terminology, which will facilitate an immediate translation of results from one approach to the other.