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. 2019 May 1;26(Pt 3):700-707.
doi: 10.1107/S1600577519003412. Epub 2019 Apr 26.

Photon diagnostics at the FLASH THz beamline

Rui Pan  1 , Ekaterina Zapolnova  1 , Torsten Golz  1 , Aleksandar J Krmpot  2 , Mihailo D Rabasovic  2 , Jovana Petrovic  3 , Vivek Asgekar  4 , Bart Faatz  1 , Franz Tavella  5 , Andrea Perucchi  6 , Sergey Kovalev  7 , Bertram Green  7 , Gianluca Geloni  8 , Takanori Tanikawa  8 , Mikhail Yurkov  1 , Evgeny Schneidmiller  1 , Michael Gensch  9 , Nikola Stojanovic  1
Affiliations

Photon diagnostics at the FLASH THz beamline

Rui Pan et al. J Synchrotron Radiat. .

Abstract

The THz beamline at FLASH, DESY, provides both tunable (1-300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.

Keywords: FLASH; FTIR; THz diagnostic; electro-optic; intense THz.

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Figures

Figure 1
Figure 1
Scheme of the FLASH1 THz photon sources. (a) The THz undulator is located downstream of the XUV undulators, separated by free space. The electron beam dump magnet follows the THz undulator. (b) Representation of the pulse energies that can be obtained at FLASH1 from the XUV and THz sources over a wide spectral range.
Figure 2
Figure 2
THz undulator spectral range. The shaded area represents the range where the fundamental frequency of the THz undulator radiation can be reached for FLASH1 as a function of the FEL XUV wavelength (lower horizontal axis) and the electron beam energy in the linac (upper horizontal axis).
Figure 3
Figure 3
Scheme of the THz beamline in the FLASH1 experimental hall. THz beam is delivered to the end-station at the BL3 XUV beamline, via one of the two branches.
Figure 4
Figure 4
THz pulse energies measured at the beamline end-station for different conditions of the FLASH accelerator. The blue dashed line shows the beamline transmission, calculated using the SRW software package (Chubar & Elleaume, 1998 ▸).
Figure 5
Figure 5
THz pulse waveforms measured by arrival-time-sorted time domain spectroscopy (TDS). (a) The THz pulse produced by the undulator set at the nominal wavelength of 155 µm (1.93 THz). The unfiltered temporal profile is shown by the blue line and the filtered by the red line, with 155 µm (1.93 THz) bandpass filter (15% bandwidth). (b) The unfiltered THz pulse at 43 µm (7 THz) (green line). (c) The corresponding THz pulse spectra.
Figure 6
Figure 6
(Top) THz transverse beam profiles at FLASH. (a) Dump magnet (the THz undulator is off), and (b) THz undulator tuned to 88 µm (3.4 THz), unfocused beam profiles measured in the THz hutch; beam position imaged 10 m from the virtual source. Note that the undulator profile is padded with zeros to fill in the same image size. (Bottom) The same beams focused. (c) Dump magnet beam (600 µm FWHM), and (d) THz undulator beam (350 µm FWHM).
Figure 7
Figure 7
THz undulator beam size at 160 µm (1.87 THz) and its propagation. (a) Beam size measured at five different locations along the beam path (red circles) fitted by a Gaussian beam propagation. (b) THz beam propagation over the 10 m path, with the focusing mirrors inserted at the 1 m and 7 m position marks. The THz beam was approximated by fitted Gaussian beam (FWHM) (green curve) and calculated from the source by SRW (FWHM) (brown curve) and 6σ (red curve).
Figure 8
Figure 8
Scheme of the lamellar grating interferometer. OAP: off-axis parabolic mirror.
Figure 9
Figure 9
FTIR measurement for THz edge radiation with 215 µm (1.4 THz) THz bandpass filter. (a) Double-sided interferogram. (b) Respective spectrum (red curve) and air transmission with water vapor (in blue) show the strong absorption lines in this spectral range.
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References

    1. Asgekar, V., Geloni, G., Kocharyan, V., Stojanovic, N., Michel, P. & Gensch, M. (2014). Infrared Phys. Technol. 64, 26–32.
    1. Azima, A., Düsterer, S., Radcliffe, P., Redlin, H., Stojanovic, N., Li, W., Schlarb, H., Feldhaus, J., Cubaynes, D., Meyer, M., Dardis, J., Hayden, P., Hough, P., Richardson, V., Kennedy, E. T. & Costello, J. T. (2009). Appl. Phys. Lett. 94, 144102.
    1. Bell, R. J. (1972). Introductory Fourier Transform Infrared Spectroscopy. New York: Academic Press.
    1. Buzzi, M., Först, M., Mankowsky, R. & Cavalleri, A. (2018). Nat. Rev. Mater. 3, 299–311.
    1. Chubar, O. & Elleaume, P. (1998). Proceedings of the Sixth European Particle Accelerator Conference (EPAC’98), 22–26 June 1998, Stockholm, Sweden, pp. 1177–1179.