The AILES Beamline use two Bruker 125 Interferometers (Branch A and B) as stations for spectroscopic analysis. The collected Synchrotron Radiation (SR) can be steered by a movable mirror toward either one of these two interferometers.
The Branch B interferometer has a lower resolution (max unapodized resolution = 0.008 cm-1) and therefore should be the choice for condensed matter studies.

A complete range of optimized beam splitters and detectors is available to cover the whole near- to very far infrared range. The strong point of the AILES Beamline being experimentation in the far IR, a special effort has been the implementation of fast bolometers (ca. 1 kHz bandpass) enabling an increase in signal to noise ratio (S/N) with respect to standard detectors.

Attenuated Total Reflection (ATR) is a sampling technique which enables solid, liquid or thin films samples to be examined directly in the infrared range. The ATR uses the evanescent wave, a property of total internal reflection to probe the sample. A beam of infrared light is passed through the ATR crystal in such a way that it reflects off the internal surface in contact with the sample.
This reflection gives rise to the evanescent wave which extends into the sample. The penetration depth into the sample is typically close to the wavelength of light, but is also affected by the angle of incidence and the indices of refraction for the ATR crystal and the medium being probed. This results in the technique to be adapted to the spectral range: a long path in the far infrared where the sample is usually less absorbing and a shorter path in the mid infrared where the sample usually absorbs more.

As the AILES beamline is working under vacuum, we have developed a mechanical device combining the ATR optics of a commercial set-up (Smart-Orbit, ThermoNicolet) and the sample compartment of the spectrometer under vacuum. With this configuration the entire optical path is under vacuum (preventing atmospheric water vapour absorption) except for the attenuated wave redirected toward the sample pressed at the diamond crystal interface. In addition, as the set-up optics only exploits reflective optics (no refocusing lenses are used) this configuration is adapted to the entire visible, infrared and THz ranges.
Furthermore, although the interferometer is evacuated and changing samples does not require breaking the vacuum system. Other advantages consist in the ability to obtain a reference by measuring a simple "total reflection" (without pressed sample).

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A cryogenic system allowing infrared transmission measurements for samples at temperature ranging from 400K to 4K has been developed for the condensed matter measurements (branch B). This system includes a pulse tube Helium close cycle cryogenerator provided by Cryomech (PT 405) working with a closed loops of helium cooling down samples at 4K in 1h30.

A specific chamber connected to the spectrometer IFS125 BRUKER, the cold head and the sample holder of the cryostat were designed and developed at SOLEIL (see figure below). Specific optic reduces the spot size at the sample by a factor 2 allowing measurement of small sample (less than 1mm) as well as an optimal alignment under vacuum. The vacuum level of the spectrometer and the beam-line (less than 10-5 mbar) allows connecting directly (without supplementary windows) the cryostat chamber and the spectrometer thus avoiding absorption and/or multiple fringes by windows.

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Specifics sample holders adapted for solid samples, pellets and liquid samples have been developed.

The laboratory LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques CNRS-University Paris 7 and 12), in association with the AILES team is currently developing such a cell. The goal is to generate optical paths of the order of hundred meters in a controlled enclosure between 350 and 100K, with vacuum systems capable of handling the appropriate gas mixtures without generating extraneous vibration, harmful to the quality of the measure.
The major challenges of the system are:
• Allowing an optical path of 150 m with at least 10% transmission.
• Compatibility with a wide optical range (2 to 300 µm).
• High stability and accuracy measurements even at low temperature and pressure.
We chose an optical set-up as proposed by S. Chernin [1] because it allows the use of the entire surface of the mirror field, through the use of a system of 5 mirrors (figure 1). This set-up can generate longer optical paths and has a lower sensitivity to vibrations and deformations. The maximum optical path will be 144 meters and the minimum of one pass in the cell will be 4 meters.
Usual device for cooling cell requires a continuous flow of cryogenic fluid, whose regulation generates low frequency vibration, inconsistent with the operation of a Fourier Transform spectrometer. A design with four walls was chosen : an inner envelope (containing the gas and the optical system), a double wall convection cooling from liquid nitrogen and an inert gas, and an outer vacuum cell for the first three-walled cell (figure 2). The temperature range will be 80-300 K ±1K. The pressure will be controlled from 100 to 0.1 with an accuracy of 0.001 mbar. Because of the lower accuracy of commercial cryogenic pressure gauges, we are developing a home-made pressure gauge in collaboration with the vacuum group to reach the 0.001 mbar accuracy, based on capacitive sensors using flexible electrodes.

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Gas

This discharge cell of relatively large diameter (13 cm) and length (110 cm) has been specially designed for an optimal coupling with the Bruker FT interferometer using either internal sources or synchrotron emission continua. A set of gold coated spherical concave mirrors with 82.5 mm diameters is placed in a White-type arrangement and allows an absorption path length of 24 meters. These three spherical concave mirrors have a 1000 mm radius of curvature. The cell is connected to the spectrometer by means of two DN25 to enter and exit the modulated infrared light.


The stainless steel water cooled electrodes, supplied by a continuous high voltage (1 kV / 2 A), create a high current discharge. Several inlets in the Pyrex discharge tube are used to continuously inject mixture of helium (He) and precursors species. Relatively fast gas flow (required to record absorption spectra of transient species) is obtained thanks to an EH500 Edwards booster pump associated to an ACP28 primary dry pump. Thanks to the relatively long absorption path length of the cell, the synchrotron radiation source and the direct probe inside the positive column of the discharge where radicals are produced, this absorption technique appears quite sensitive and allows the use of the highest resolution of the interferometer.

This set-up is now open to external user groups for the study of radicals or reactive molecules.

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This set-up is placed into a separated compartment and use two focusing Cassegrain optics. Infrared measurements can be made in transmission and reflectivity, using a diamond anvil cell.
A small quantity of the sample to study is mixed to a binder transparent in infrared (polyethylene in the FIR, KBr or NaBr in the MID) and then loaded in a 250 µm hole drilled in a pre-indented gasket. A ruby inserted in this space is used to calibrate pressure. The pressure is controlled in the range up to 14GPa and the set-up allow measurements by steps of 1 to 2 GPa after a stabilization of for 5 to 10 min at each pressure point. The sample can be cooled down to 50K thanks to a cryostat.

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IR and far-IR absorption spectroscopy of positive ions in hollow cathode discharge.
The ISMO team received grants from the National program PCMI for the period 2009-2013 to develop an experimental set-up permitting to record absorption spectra of positive ions of astrophysical relevance using FT spectrometers. This hollow cathode cooled to liquid nitrogen optimizes the ion production in the negative glow of the discharge.

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This copper designed cell allow: (i) temperature control between 380 K and 40 K; (ii) dosage of the desired amount of adsorbed gas; (iii) pumping down to 10-6 mbar for reference measurements free from molecular adsorption. The cell was designed to study the modifications to the infrared spectra following molecular adsorption. The use of a unique cell, in a wide spectral domain, provides complementary information and insures the reproducibility of the adsorption and gas dosage.

The cell is made in copper in order to allow for good thermal exchange and has a volume of ~1 cm3 to limit gas absorption at ambient pressure. It is UHV-compatible (leak rate > 1·10-9 mbar·l/s). The cell is connected to a closed-cycle cryostat by a copper braid for cooling and temperature resolved experiments (from 40 K to 380 K). A thermocouple and a resistive heater allow controlling the sample temperature during measurements with a precision of ± 0.1 K. The cell is equipped with two diamond windows (10 mm in diameter, 0.5 mm in thickness at center, 0.5° wedge) allowing to measure the transmission of material from the THz to the mid infrared region with reduced spectral channelling effects. The sample is fixed on a sample holder at precise normal incidence relative to the incident beam. An entry for the gas input/output or the vacuum pump is also present in the body of cell. Gas dosage can be done in static conditions.

During hydration measurements, the system is studied at equilibrium for a given value of relative humidity (defined as the ratio of partial water vapour pressure p and water vapour pressure p0 (31.7 mbar at 25°C) at a given temperature, RH=(p/p0)*100). A tube containing outgassed deionized liquid water (18.2 MΩ·cm-1 at 25°C) provides the vapour source. The vapour pressure is monitored by a thermostated gauge (0-100 mbar at ±0.02 mbar) and, once at equilibrium, the measurements are performed.

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Gas

The A513/Q Bruker reflection accessory allows the measurement of the solids (or liquids) reflectivity for variable incidence angles between 13 and 85 degrees. The sample is placed in the horizontal plan of the set. The development of a motorized translation stage allows the simultaneous positioning and then the successive measurement of reflectance for 3 different samples. This setup is particularly well adapted for the study of non-transparent materials (Infrared Refection Absorption Spectroscopy of monolayers or sub-monolayers, Langmuir-Blodgett films, corrosion analysis, semiconductors,…). The control of the angle of incidence is made directly through the acquisition software, without breaking the vacuum in the spectrometer. The coupling with a motorized polarizer (also computer controlled) is possible.

The unit A510/Q-T is an accessory designed for both transmission and reflection measurements mainly in the MIR region. The great advantage of this unit is that the sample can be measured in transmittance and reflectance at exactly the same spot without the need of interrupting the spectrometer purge or venting the sprectometer (when working under vacuum condition). Typical applications are the spectroscopic analysis of solids (e.g. crystals, semiconductors), optical filters and window materials, accurate absorbance determination as well as low temperature transmittance and reflectance studies.

The motorized polarizer holder A121 allows a computer-controlled operation of the polarizer, i.e. measurement at different polarization angles without the necessity of opening the spectrometer sample compartment are possible. The polarizer holder can be rotated by 360° with an angle resolution of 0.25°.

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Absorption FTIR spectroscopy in supersonic jets combines several advantages: (i) very low rovibrational temperatures attainable in supersonic expansions are essential to reproduce not only the diluted and cold environments of planetary atmosphers but also to simplify the spectral congestion within rovibrational bands of polyatomic molecules, as well as to stabilize weakly bound molecular complexes, (ii) the broad spectral coverage of the interferometer enables to realize precise structural studies for a large variety of molecular systems, (iii) finally the detection sensitivity of this spectroscopic tool can be notably improved due to the availability of large molar flows and to the implementation of efficient optical multipass devices , particularly when using the low divergent synchrotron radiation.

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The transmission studies of liquids as a function of the temperature in the range -75°C to 100°C is offered on the AILES beamline. The set-up is composed of a motorized tree axis motion, which allows the adjustment of the cell containing the sample without breaking the vacuum.
This tree axis supports a sample holder and the circulating liquid system for cooling or heating the sample. Various windows (Diamond, Polyethylene, TPX, CaF2, ZnSe) allow spectroscopic studies in all the infrared range from 5cm-1 to 20000cm-1.
The thickness of the sample is defined by Mylar spacers ranging from 1 μm to 100 μm. In order to measure the temperature of the sample a Pt100 sensor is connected to the liquid cell containing the sample.

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Liquid

To analyze metal-ligand vibrations and provide key answers for the understanding of metal site properties in metalloproteins and in metallocomplex, the Far-infrared (Far-IR) difference spectroscopy technique is the ideal tool.
In order to extract the part of the signal corresponding to the metal-ligand vibrations imbedded in the massive water absorption, it is necessary to record difference spectra obtained at specific points during an oxidoreductive cycle applied on liquid samples.
This transmission cell is an optimization of an existing set-up equipped with 2 CVD diamond windows (transparent in the 2000 to 50 cm-1 spectral range) together with a 4µm thick gold grid as a working electrode.
This set-up has been adapted for use with the synchrotron beamline AILES spectrometers. In particular, it can work under vacuum a necessary condition to increase the stability of the optics, the sensitivity of the measurements (less than 10-4 unity of absorbance), and hence the spectral resolution.

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Liquid

This multipass cell consists in a stainless steel cylindrical vacuum chamber of 2853 mm length and 600 mm diameter equipped with three mirrors in a White-type arrangement. The hard gold coated optics are spherical concave mirrors with 2526 mm radius of curvature and diameters of about 200 mm. An absorption path length of about 10 up to 180 m can be reached in this cell. Using this set-up one can perform gas-phase absorption spectroscopy in the FIR region for several kinds of samples. Thanks to the relatively long absorption pathlength, pure rotation as well as rovibration transitions of low frequency modes were obtained for samples with low vapor pressure at room temperature. Since 2009, 17 external projects have been successfully realized with that set-up (8 publications, 2 accepted papers). For more absorbing compounds, a smaller cell is available to cover the 0.8- 8 meter path length range.

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Gas