We present a very simple formula for calculating the total number of photons of an x-ray beam after being monochromatized by a double crystal monochromator. This is a typical case for most synchrotron radiation beamlines. The derivation of the formula and its numerical benchmarking by ray-tracing simulations are also presented.
After a brief review of the research and development activities on the control of the time structure of x-ray beams conducted at the European Synchrotron Radiation Facility, we present first results of the performance of an optical chopper based on a vibrating crystal device. With this system we were able to select time windows from about 200 ns to infinite with a repetition rate of 20 kHz and the high throughput provided by the high reflectivity of perfect single crystals.
The diffraction of an X-ray beam on an ultrasonic wave propagating at the surface of a crystal gives rise to diffraction satellites whose temporal structure is correlated to the one of the ultrasonic wave. Two different applications of this phenomenon are presented in this paper: By matching the temporal structure of the surface acoustic wave (SAW) with the filling mode of the storage ring, it is possible to pick or reject the incident X-ray pulses and thus to build a chopper working in the MHz range. The second application deals with binary data transfer by an X-ray beam. The experiment consists in modulating the signal fed to the acoustic transducer with a signal carrying digital data, which is a way of transmitting this information into the X-ray beam satellite.
In an earlier paper the emission of synchrotron radiation was studied theoretically for the current induced by a single electron interacting with a bending magnet showing that a chirp of the hard x-ray could be expected that could be used for a compression of x-ray bunches using dispersive optics. In this paper we will present results of an experimental study that was conducted on a bending magnet beamline (BM5) at the ESRF to learn if such a chirp exists for an electron bunch as a function of the x-ray energy and of the emission angle below and above the electron orbit plane. Our results for the pulse shape show that such a chirp could not be clearly detected at a level of several tens of picoseconds FWHM. This means that the phase relationships of all the electrons producing the x- ray bunch are averaged out leading to the absence of a net chirp. However, a fast Fourier transform of the observed signal showed that there was a phase lag. This will be described in a companion paper. Here, the details of the experimentally observed time structure will be given.
Rene Wrobel, Bernard Brullot, Francois Dainciart, Jean Doublier, Jean-Francois Eloy, Remy Marmoret, Bruno Villette, Olivier Mathon, Remi Tucoulou, Andreas Freund
With the advent of new x-ray sources, the detection of radiation with picosecond temporal resolution becomes increasingly important. We used the time structure of the radiation at the European Synchrotron Radiation Facility (ESRF) to characterize fast detectors developed for x-ray diagnostics. The detectors tested were neutron pre-irradiated Gallium Arsenide (GaAs) detectors and chemical-vapor-deposited (CVD) diamond detectors. The experiments were performed on beamline BM5, both in single-bunch and multi-bunch mode. The response of the detectors to the hard x-ray pulses was recorded using a single shot 7 Ghz oscilloscope or using a digital oscilloscope in sampling mode. For a current of the electrons in the storage ring of typically 10 - 15 mA in monomode-bunch, the pulse length was between 100 ps and 150 ps (FWHM). In multi-bunch mode, the X-ray pulse length was independent of the current and shorter. We measured FWHM pulse duration values down to 50 ps. Comparison with data obtained with a streak camera showed that the time resolution of our detectors was at best 25 ps.
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