APPLICATIONS OF THE VUV FOURIER TRANSFORM SPECTROMETER AT SYNCHROTRON SOLEIL

Fourier transform spectrometers (FTS) are usually based upon amplitude division interferometers through beamsplitters (BS) as in the Michelson interferometer geometry. However, the manufacture of broadband BS is difficult and even impossible in the far VUV (below $lambda$ = 140 nm). We therefore conceived an instrument based upon an original design involving only reflective plane surfaces, giving access to the whole VUV range without the restrictions associated with BS. The VUV� FTS is a permanent endstation connected to one of the three experimental branches of the DESIRS beamlinefootnote{Nahon et al., J. Synchrotron Radiat., 19, 508(2012)} and devoted to high resolution photoabsorption in the UV-VUV spectral range, typically between $lambda$ = 300 and 40 nmfootnote{De Oliveira et al., Nat. Photonics, 5, 149(2011)}. Since 2008, a large international community of users interested in laboratory measurements with applications in astrophysics, molecular physics or planetary atmospheres has been attracted by the VUV - FTS capabilities including its efficiency in terms of signal to noise ratio, even when high spectral resolution was not an issue. A large number of dedicated gas phase sample environments have been developed including a windowless cell that can be cooled down, a heated windowless cell, a free molecular jet set-up and various windowed cells. Besides, a new discharge gas cell for production and study of transient species gave recently its first results. As an illustration, the VUV absorption spectrum of the chem{CH_3} radical down to 140 nm will be shown in this presentation