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Coherent synchrotron radiation for broadband terahertz spectroscopy
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Image of FIG. 1.
FIG. 1.

(a) Spectral distribution measured for α = α0/25 and for various bunch currents. The projected version at the bottom shows two thresholds: the appearance of CSR for I bunch = 55μA (threshold 1) and the appearance of strong instabilities for I bunch = 95μA (threshold 2). (b) Evolution of the fluctuation frequencies with the current. The CSR signal at around 1 THz fluctuates at a frequency in the kHz range, resulting in localized artifacts in the spectra. The two thresholds can again be observed in the projected 2D plot: the appearance of the artifacts (threshold 1) and the development of bunch instabilities (threshold 2).

Image of FIG. 2.
FIG. 2.

Top: intensity profile of the CSR produced with a momentum compaction factor of α0/25 and 416 bunches (solid line), compared to incoherent synchrotron radiation (ISR) obtained with α0 (dashed line). The intensity was normalized for a current per bunch of 1 mA. Bottom: signal-to-noise measured by dividing two successive spectra through an empty 85 cm gas cell (10 scans, 1 h, 10−3 cm−1 resolution) with the same conditions as described above for ISR and CSR.

Image of FIG. 3.
FIG. 3.

Schematic diagram of the high-resolution spectroscopic station of AILES beamline. The first beamsplitter divides the incident beam into a reflected reference beam (detected by bolometer 1) and a transmitted beam (modulated by the interferometer, then detected by bolometer 2) with R/T = 0.25 at 10 cm−1. The interferogram (temporal signal 2) includes an artifact, represented in black, which is also present on the reference signal (temporal signal 1).

Image of FIG. 4.
FIG. 4.

Artifact correction on a 45 min absorbance spectrum of N2O at 0.001 cm−1 resolution. Both the reference spectrum and the sample spectrum were acquired with 416 bunches, 64 μA/bunch, and α0/25. Top: effect of the intensity fluctuations on the raw absorbance spectrum. Bottom: same spectrum after post-processing of the data. The gain in S/N reaches at least 25 locally.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Coherent synchrotron radiation for broadband terahertz spectroscopy