Journal of large-scale research facilities, 2, A95 (2016) http://dx.doi.org/10.17815/jlsrf-2-95 Published: 24.11.2016 The IRIS THz/Infrared beamline at BESSY II Helmholtz-Zentrum Berlin für Materialien und Energie * Instrument Scientists: - Dr. Ljiljana Puskar, Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 30 8062-14739, email: ljiljana.puskar@helmholtz-berlin.de - Dr. Ulrich Schade, Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 30 8062-13449, email: ulrich.schade@helmholtz-berlin.de Abstract: At BESSY II a large acceptance angle, multipurpose infrared beamline is available, compris- ing several end stations suitable for material and life science investigations. The beamline provides highly brilliant infrared radiation over the energy range from about 20,000 down to 30 cm−1 and even lower when BESSY II is run in the so-called low-α mode. 1 Introduction Infrared radiation from synchrotron sources has seen a steady increase in research over the last decade. At synchrotron light sources of third generation like BESSY II the emitted radiation in the infrared wavelength region is some orders of magnitude brighter than standard thermal broadband sources (e.g., globar). In addition, infrared synchrotron radiation is an absolute source being polarized and pulsed in the picosecond timescale. As a particular specialty, BESSY II provides a new technique (low- α ) to generate high power, stable and low-noise coherent terahertz (THz) radiation (Abo-Bakr et al., 2003). The IRIS beamline was inaugurated in December 2001 (Schade et al., 2002) and is now used by a multi-disciplinary research community. 2 Optical Design The beamline uses radiation from the homogenous magnetic �eld (Schade et al., 2000) of the dipole D11 and its optical layout (Peatman & Schade, 2001) is shown in Figure 1. A plane extraction mirror is placed at about 900 mm from the dipole source in the plane of the storage ring allowing horizontal and vertical acceptance angles of about 60 x 40 mrad2, respectively. The mirror is split into two water-cooled halves positioned above and below the narrow high energy radiation fan in the ring plane, permitting most of *Cite article as: Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). The IRIS THz/Infrared beamline at BESSY II. Journal of large-scale research facilities, 2, A95. http://dx.doi.org/10.17815/jlsrf-2-95 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-2-95 http://dx.doi.org/10.17815/jlsrf-2-95 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A95 (2016) http://dx.doi.org/10.17815/jlsrf-2-95 the heat due to UV and X-rays to pass through to an absorber. The extraction mirror de�ects the beam upwards to a combination of two cylindrical mirrors. These mirrors then focus the beam outside the radiation shielding of the ceiling of the storage ring tunnel just behind a CVD diamond window. The diamond window separates the UHV of the storage ring from the vacuum system of the remainder of the beam line. The subsequent optical elements direct the light to the di�erent experiments. In addition, an ellipsometer (Gensch et al., 2006) is attached to a vacuum FT-IR spectrometer. Figure 1: Schematic of the optical layout of the IRIS beamline. 3 Beamline Performance Figure 2: Calculated brilliance in the infrared spectral range for the IRIS beamline at BESSY II and for a globar source. 2 http://dx.doi.org/10.17815/jlsrf-2-95 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-95 Journal of large-scale research facilities, 2, A95 (2016) Figure 3: In the mid infrared range, more than one order of magnitude more �ux can be fed through apertures smaller than 10 x 10 µ m2 when compared to a globar source. This allows one to perform di�raction-limited microspectroscopy. Data were taken with a Nicolet Continuµm infrared microscope in confocal transmission geometry using the internal instrument aperture with no sample in the focal plane. Figure 4: Comparison of �uxes in the far IR/THz range. Running BESSY II in the low-α mode yields coherent synchrotron radiation (CSR) at the IRIS beamline with �uxes several orders of magnitudes higher than obtained with incoherent infrared synchrotron radiation (IRSR) or with internal spectrom- eter sources (Hg lamp). An rms noise of better than 0.1% is achieved from the CSR source as indicated by the 100% line, the ratio of two subsequently recorded spectra. Data were taken in vacuum using a Bruker 66/v spectrometer (Schade et al., 2007). 3 http://dx.doi.org/10.17815/jlsrf-2-95 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A95 (2016) http://dx.doi.org/10.17815/jlsrf-2-95 4 Experimental Stations • Vacuum FT-IR Spectrometer NIR, MIR, FIR • Ellipsometer (operated by ISAS) MIR • Martin-Pupplet Spectrometer FIR (THz) • Near-�eld Microscope FIR (THz) • Scanning Microscope MIR • Vacuum Microscope FIR (THz), MIR Samples can be investigated with di�erent polarization states of the light under several geometries (e.g., transmittance, grazing and normal incidence re�ectance, di�use re�ectance, ATR) and for di�erent environmental conditions, like pressure and temperature. 5 Technical Data Location 3.1 Source D11 Energy Range 2 – 10,000 cm−1 Horizontal Source Acceptance 60 mrad Vertical Source Acceptance 40 mrad Polarisation - linearly horizontal/vertical - circularly left and right handed Spectrometer Fourier Transform Spectrometer Energy Resolution 0.125 cm−1 Focus Size at Sample di�raction limited Free Photon Beam available yes Fixed End Station microscopes, spectrometers, ellipsometer Table 1: Technical data of the IRIS Beamline. References Abo-Bakr, M., Feikes, J., Holldack, K., Kuske, P., Peatman, W. B., Schade, U., . . . Hübers, H.-W. (2003). Brilliant, coherent far-infrared (THz) synchrotron radiation. Phys. Rev. Lett., 90, 094801. http://dx.doi.org/10.1103/PhysRevLett.90.094801 Gensch, M., Korte, E., Esser, N., Schade, U., & Hinrichs, K. (2006). Microfocus-infrared syn- chrotron ellipsometer for mapping of ultra thin �lms. Infrared Physics & Technology, 49(1–2), 74-77. http://dx.doi.org/10.1016/j.infrared.2006.01.007 Peatman, W. B., & Schade, U. (2001). A brilliant infrared light source at BESSY. Review of Scienti�c Instruments, 72(3), 1620-1624. http://dx.doi.org/10.1063/1.1347976 Schade, U., Ortolani, M., & Lee, J. (2007). Technical Report: THz Experiments with Co- herent Synchrotron Radiation from BESSY II. Synchrotron Radiation News, 20(5), 17-24. http://dx.doi.org/10.1080/08940880701631351 4 http://dx.doi.org/10.17815/jlsrf-2-95 http://dx.doi.org/10.1103/PhysRevLett.90.094801 http://dx.doi.org/10.1016/j.infrared.2006.01.007 http://dx.doi.org/10.1063/1.1347976 http://dx.doi.org/10.1080/08940880701631351 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-95 Journal of large-scale research facilities, 2, A95 (2016) Schade, U., Röseler, A., Korte, E., Scheer, M., & Peatman, W. (2000). Measured characteris- tics of infrared edge radiation from BESSY II. Nuclear Instruments and Methods in Physics Re- search Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 455(2), 476 - 486. http://dx.doi.org/10.1016/S0168-9002(00)00507-6 Schade, U., Röseler, A., Korte, E. H., Bartl, F., Hofmann, K. P., Noll, T., & Peatman, W. B. (2002). New infrared spectroscopic beamline at BESSY II. Review of Scienti�c Instruments, 73(3), 1568-1570. http://dx.doi.org/10.1063/1.1423781 5 http://dx.doi.org/10.17815/jlsrf-2-95 http://dx.doi.org/10.1016/S0168-9002(00)00507-6 http://dx.doi.org/10.1063/1.1423781 https://creativecommons.org/licenses/by/4.0/ Introduction Optical Design Beamline Performance Experimental Stations Technical Data