Synchrotron radiation constitutes a high flux and brightness broad band source used in various facilities around the world.
Beam intensity profile (near 1000 cm-1) at the interferometer entrance focal plane on AILES.
For example, around 1000 cm-1, the beam, although slightly asymmetrical in profile due to the asymmetry in the emission and shape in the front extraction mirror, can focussed to have 95 % of the total flux ( 5 x 1013 photons/sec/cm-1) contained within 0.75 mm from the beam axis.
Φmeasured = 4.5 ± 1.5 1013 photons/s/0.1% B.P. @ IRS = 500
Such properties are crucial for studies limiting the source or sample surface area such as condensed studies on small sample cells or crystals and high resolution gas phase work.
For high resolution studies, the input SR IR beam can be used in many instances without entrance iris (Note that the effective beam size at the spectrometer entrance varies with wavelength, a good rule of thumb being d(mm) = 25 (ν (in cm-1)-½ ).
The following figure presents the S/N enhancement achieved for high resolution measurement as measured at AILES :
Thus, for instance, a 6-fold enhancement means that achieving a measurement with an equivalent S/N ratio using a lab source would require some 36 days of measurement around 200 cm-1 to reach a S/N ratio of about 80, while this can be achieved in one day using SR...
Also, the dependence in beam size following approximatively the requirement in source size for work at the highest resolution, optimum conditions can be met in one measurement without repeating measurements with different aperture stops, which means that a great amount of time can be saved, as the measurement does not need to be repeated several times with different iris sizes, if several rovibrational bands can be covered with the same detector-beamsplitter combination. So, supposing that your sample presents one band near 200 cm-1 and another one near 400 cm-1 ,that you both want to record at high resolution, your measurement can still take about one day using SR, while it should be repeated with a different aperture stop with a globar source, adding another 20 days or so of continuous recording operating liquid He-cooled detectors or cells in the same experimental conditions....
Comparison of two successive HR measurements with aperture stop Ø = 1.5 mm (red) and without aperture stop (black). Detail of one the low J R branch cluster of the ν4 band of OsO4.
Beamline poster
