A simple method for timing an XFEL source to high-power lasers

Abstract

We propose a technique, to be used for time-resolved pump-probe experiments, for timing an x-ray free electron laser (XFEL) to a high-power conventional laser with femtosecond accuracy. Our method takes advantage of the same electron bunch to produce both an XFEL pulse and an ultrashort optical pulse with the help of an optical radiator downstream of the x-ray undulator. Since both pulses are produced by the same electron bunch, they are perfectly synchronized. Application of cross-correlation techniques will allow to determine relative jitter between the optical pulse (and, thus, the XFEL pulse) and a pulse from an external pump-laser with femtosecond resolution. Technical realization of the proposed timing scheme uses an optical replica synthesizer (ORS) setup to be installed after the final bunch-compression stage of the XFEL. The electron bunch is modulated in the ORS setup by an external optical laser. Subsequently, it travels through the main undulator, and produces the XFEL pulse. Finally, a powerful optical pulse of coherent edge radiation is generated as the bunch passes through a long straight section and a separation magnet downstream of the main undulator. Our study shows that at a moderate (about 10%) density modulation of the electron bunch at the location of the optical radiator allows production of high power x-ray and optical pulses. Relative synchronization of these pulses is preserved by using the same mechanical support for both x-ray and optical elements transporting radiation down to the experimental area, where single-shot cross-correlation between optical pulse and pump-laser pulse is performed. We illustrate the potential of the proposed timing technique with numerical examples referring to the European XFEL facility.Comment: Version 2: Reference list updated; submitted for publication. 21 pages, 8 figure

Response-time-improved ZnO scintillator by impurity doping

“…For ultrafast light sources, such as the X-ray free electron laser, a temporal resolution of at least a few picoseconds is necessary. Therefore, despite this improvement of over one order of magnitude the 10 ps decay time is still insufficient for the applications stated earlier [7,11].…”

Optical afterburner for an x-ray free electron laser as a tool for pump-probe experiments

“…Thus, by varying R 56 one can easily optimize the form factor in the wavelength range from VUV to infrared. Let us now discuss how to produce radiation that can be transported to the experimental hall and used in pumpprobe experiments as described in [15]. In principle, one can make use of edge radiation [15].…”

“…If the optical pulse is sufficiently powerful, it can be directly used in a pump-probe experiment. Otherwise this long-wavelength radiation pulse can be used for a cross-correlation measurement with a powerful pulse from a conventional laser (that is used in the pumpprobe experiment) [15]. This allows one to determine a relative delay between two pulses for every shot and then to sort out experimental data using this information.…”

“…This allows one to determine a relative delay between two pulses for every shot and then to sort out experimental data using this information. Different scenarios were considered [13][14][15][16][17] for producing visible or infrared radiation by the same electron bunch that lases in an x-ray undulator.…”

Energy slicing analysis for time-resolved measurement of electron-beam properties

“…Often being larger than the FEL pulse duration, these values can seriously limit the possibility of certain pump-probe experiments. Therefore, special diagnostics have been proposed [23] and implemented [21,24] to monitor simultaneously the electron beam and the FEL pulse jitter, in order to allow correction of the collected pump-probe data.…”