Seminars Archive
Synchrotron infrared source: production and applications in microspectroscopy
Abstract
Friday, November 8, 2002, 11:00
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Synchrotron infrared source: production and applications
in microspectroscopy
Paul Dumas
( LURE-CNRS Centre Universitaire Paris Sud, Orsay Cdex)
Abstract
Synchrotron radiation, emitted either from dipole bends and edges, is
a high-brightness infrared source, which is well suited to spectroscopy.
The spectral range, which extends from about 2.5 to 20 micron, so-called
mid-infrared region, spans most of the vibrational mode frequencies necessary
to a detailed identification of functional chemical groups. Flux and brightness
for the two emission modes are comparable. Brightness is crucial for infrared
microscopy when one is trying to illuminate a small area as possible with
as much light as possible. Accordingly, IR microscopic analysis have became
diffraction-limited, typically half of the probed wavelength in confocal
configuration .
Synchrotron infrared beamlines relies not only on brightness, but also
on beam stability, an important parameter for signal-to-noise issues, and
reduced recording time.
The applications are multidisciplinary, and some examples will be illustrated:
durst particles, polymer interfaces, geological inclusions. It should be
noticed that synchrotron IR microscopy has led to numerous biological studies.
Biological samples have been examined with IR microscopes equipped with
conventional IR sources for nearly 20 years. However, although conventional
IR microspectroscopy has proven extremely valuable for resolving the chemical
composition in biological samples, the existing instruments encounter a
signal-to-noise limitation when apertures confine the IR beam to an area
of 20-30 microns in diameter. This prohibits, for example, the study of
individual biological cell, which are typically of 5-30 microns in diameter.
Despite their complex composition, biological tissues exhibit a rather
simple infrared spectrum. The high signal to noise ratio achieved with
a synchrotron source, even with very small apertures, results in high-contrast
spectroscopy and imaging. IR imaging involves the acquisition of a series
of spectrum. When all components with different absorption intensity are
known, the resulting image of this component is obtained straightforwardly
by plotting (x,y,I( )). However, as it is often the case in biological
science, the components, and the expected changes in the spectra are not
known in advance. Therefore, multivariate statistical analysis can be efficiently
applied, thanks to the high signal to noise spectra obtained.
I will illustrate the different cases for the study of individual cells,
skin, hair and brain plaques.
Synchrotron infrared microscopy is nowadays becoming a highly potential
complementary analytical tool, with other synchrotron based- microscopic
technique. More particularly, combined X-rays and IR imaging studies on
the same sample (hair skin and brain plaques) will be presented.
It is worth noting that the infrared source is pulsed, and pump-probe experiments
can then be carried out. I will show recent pump-probe experiment done
at LURE using the FEL-UV and the IR microscope.
