If the traditional domain of excellence of synchrotron radiation is that of X-rays, SOLEIL also represents a currently irreplaceable broad band source for high resolution infrared (IR) spectroscopy because of its high brilliance. Researchers from SOLEIL and other synchrotrons in the world take advantage of this property for IR absorption gas analysis. To optimize the benefits of this exceptional source, scientists of the AILES beamline and the Detectors Group at SOLEIL have developed a special device which delivers a significant increase in sensitivity –approximately one order of magnitude– compared to the existing commercial systems.
Work in the infrared domain is characterized by the fact that, in this wavelength range, we are immersed in a high ambient radiation flux which is emitted by all of the objects and bodies that surround us (including ourselves…, a property that is exploited by night vision systems and other military applications). Therefore the difficulty for spectroscopists working in this range is subtracting this "parasite" radiation which adds itself to the flux they are trying to detect, thereby degrading the measurements. The device developed at SOLEIL for IR spectroscopy is based firstly on special optics cooled to -269°C to as far as possible remove this effect and limit the thermal agitation in the semiconductor material constituting the sensitive element of the device. And it also relies on the reduction of the viewing angle via which the sensitive element receives the photon flux. In addition, a high sensitivity, reduced noise electronic system has been developed by the engineer and technician of the Detectors group to complete the device.
This technology of cooling to a very low temperature combined with a special electronic system has improved, by an order of magnitude, the quality of information relating to the infrared absorption of gaseous compounds (see Figure 1). This device has already been applied to measuring the infrared absorption of certain atmospheric pollutants (SF6, phosgene, sulfuryl fluoride, freons, halomethanes, etc.) or hydrocarbons identifiable in distant planetary atmospheres (ethylene, propane, butane, allene on Titan).
Figure: Performance comparison between the infrared detector developed at SOLEIL and the standard available detector. Here we compare the detection of CO2 absorption by the two types of detectors under the same conditions.