Abstract
Today, the vast majority of electron storage rings delivering synchrotron radiation for general user operation offer a dedicated infrared port. There is growing interest expressed by various scientific communities to exploit the mid-IR emission in microspectroscopy, as well as the far infrared (also called THz) range for spectroscopy. Compared with a thermal (laboratory-based source), IR synchrotron radiation sources offer enhanced brilliance of about two to three orders of magnitude in the mid-IR energy range, and enhanced flux and brilliance in the far-IR energy range. Synchrotron radiation also has a unique combination of a broad wavelength band together with a well defined time structure. Thermal sources (globar, mercury filament) have excellent stability. Because the sampling rate of a typical IR Fourier-transform spectroscopy experiment is in the kHz range (depending on the bandwidth of the detector), instabilities of various origins present in synchrotron radiation sources play a crucial role. Noise recordings at two different IR ports located at the Swiss Light Source and SOLEIL (France), under conditions relevant to real experiments, are discussed. The lowest electron beam fluctuations detectable in IR spectra have been quantified and are shown to be much smaller than what is routinely recorded by beam-position monitors.
Highlights
Most of the experiments performed at the infrared ports of synchrotron radiation facilities involve the use of Fourier transform infrared (FTIR) spectrometers [see, for example, Griffiths & de Haseth (1986) and Quack & Merkt (2011)]
In order to emphasize the practical benefit on spectral quality obtained at the Swiss Light Source (SLS) IR port when the noise owing to the RF power supply sub-system is suppressed, we show in Fig. 9 the ratio of two consecutive measurements, with and without noise source
We confirmed that the beam stabilization tools (BPM and feedback systems) installed at two third-generation storage rings are capable of stabilizing the beam position below 1 mm in a bending magnet, and that this performance matches the requirements for IR spectroscopy
Summary
Most of the experiments performed at the infrared ports of synchrotron radiation facilities involve the use of Fourier transform infrared (FTIR) spectrometers [see, for example, Griffiths & de Haseth (1986) and Quack & Merkt (2011)]. Complex dynamic feedback systems (Hubert et al, 2009; Schilcher et al, 2004) that use beam-position monitor (BPM) (Hubert et al, 2007; Dehler et al, 1999) data as input have been designed and installed in order to maintain and monitor the short- (typically below 1 mm vertical and horizontal up to 100 Hz) and long-term stability of the electron beam orbit Despite all these efforts, noise still limits the performance of IR beamlines and must be investigated. In order to investigate various noise sources and quantify their impact on IR spectroscopic research, we measured noise across a wide frequency range, present at two different IR ports, SLS and SOLEIL These two storage rings have quite similar electron energies, sizes and performances. We use the constant field branch of the SMIS beamline
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