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Generation of doublet spectral lines at self-seeded X-ray FELs

Abstract

Self-seeding schemes, consisting of two undulators with a monochromator in between, aim to reduce the bandwidth of SASE X-ray FELs. We recently proposed to use a new method of monochromatization exploiting a single crystal in Braggtransmission geometry for self-seeding in the hard X-ray range. The obvious and technically possible extension is to use such kind of monochromator setup with two -or more- crystals arranged in a series to spectrally filter the SASE radiation at two -or more- closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet- or multiplet-spectral lines. Applications exist over a broad range of hard X-ray wavelengths involving any process where there is a large change in cross section over a narrow wavelength range, as in multiple wavelength anomalous diffraction techniques (MAD). In this paper we consider the simultaneous operation of the LCLS hard X-ray FEL at two closely spaced wavelengths. We present simulation results for the LCLS baseline, and we show that this method can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band, i.e. within 10 eV. An interesting aspect of the proposed scheme is a way of modulating the  More>>
Authors:
Geloni, Gianluca; [1]  Kocharyan, Vitali; Saldin, Evgeni [2] 
  1. European XFEL GmbH, Hamburg (Germany)
  2. Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
Publication Date:
Nov 15, 2010
Product Type:
Technical Report
Report Number:
DESY-10-199
Subject:
43 PARTICLE ACCELERATORS; BEAM BUNCHING; BEAM MONITORING; BEAM TRANSPORT; BRAGG REFLECTION; COHERENT RADIATION; ELECTRON BEAMS; EMISSION SPECTRA; ENERGY LOSSES; FREE ELECTRON LASERS; HARD X RADIATION; LASER RADIATION; MODULATION; MONOCHROMATIC RADIATION; MONOCHROMATORS; MONOCRYSTALS; ONDULATOR RADIATION; OPTICAL SPECTROMETERS; SIMULATION; SYNCHRONIZATION; TRANSITION RADIATION; WIGGLER MAGNETS; X-RAY LASERS; X-RAY SPECTRA
OSTI ID:
21394980
Research Organizations:
Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
Other: ISSN 0418-9833; TRN: DE11F0888
Availability:
Commercial reproduction prohibited; INIS; OSTI as DE21394980
Submitting Site:
DEN
Size:
21 pages
Announcement Date:
Aug 31, 2011

Citation Formats

Geloni, Gianluca, Kocharyan, Vitali, and Saldin, Evgeni. Generation of doublet spectral lines at self-seeded X-ray FELs. Germany: N. p., 2010. Web.
Geloni, Gianluca, Kocharyan, Vitali, & Saldin, Evgeni. Generation of doublet spectral lines at self-seeded X-ray FELs. Germany.
Geloni, Gianluca, Kocharyan, Vitali, and Saldin, Evgeni. 2010. "Generation of doublet spectral lines at self-seeded X-ray FELs." Germany.
@misc{etde_21394980,
title = {Generation of doublet spectral lines at self-seeded X-ray FELs}
author = {Geloni, Gianluca, Kocharyan, Vitali, and Saldin, Evgeni}
abstractNote = {Self-seeding schemes, consisting of two undulators with a monochromator in between, aim to reduce the bandwidth of SASE X-ray FELs. We recently proposed to use a new method of monochromatization exploiting a single crystal in Braggtransmission geometry for self-seeding in the hard X-ray range. The obvious and technically possible extension is to use such kind of monochromator setup with two -or more- crystals arranged in a series to spectrally filter the SASE radiation at two -or more- closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet- or multiplet-spectral lines. Applications exist over a broad range of hard X-ray wavelengths involving any process where there is a large change in cross section over a narrow wavelength range, as in multiple wavelength anomalous diffraction techniques (MAD). In this paper we consider the simultaneous operation of the LCLS hard X-ray FEL at two closely spaced wavelengths. We present simulation results for the LCLS baseline, and we show that this method can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band, i.e. within 10 eV. An interesting aspect of the proposed scheme is a way of modulating the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating ''mode-beat'' component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. Thus, at saturation one obtains FEL-induced modulations of energy loss and energy spread in the electron bunch at optical frequency. These modulations can be converted into density modulation at the same optical frequency with the help of a weak chicane installed behind the baseline undulator. Powerful coherent radiation can then be generated with the help of an optical transition radiation (OTR) station,which have important applications. In this paper we briefly consider how the doublet structure of the XFEL generation spectra can be monitored by an optical spectrometer. Furthermore, the OTR coherent radiation pulse is naturally synchronized with the X-ray pulses, and can be used for timing the XFEL to high power conventional lasers with femtosecond accuracy for pump-probe applications. (orig.)}
place = {Germany}
year = {2010}
month = {Nov}
}