Synchrotron IR source

It is clear that the introduction of the IR FPA detector has brought Fourier transform infrared (FTIR) microscopy with a thermal source to a new and exciting stage of development. This is illustrated in the other chapters of this volume. Our purpose in this chapter is to address how IR FPA technology could be combined with the synchrotron source to advance IR spectroscopic imaging in ways that would prove quite difficult with a conventional thermal source. To address this question, we will need to understand the detailed nature of the synchrotron IR source, the optical... 

The first demonstration of FT-IRM with a synchrotron IR source was made during the early 1990s, when a custom-built IR microscope was installed at the National Synchrotron Light Source (Upton, NY, USA) [16,17], while similar efforts were underway at UVSOR in Japan at the same time [18]. The first commercial IR microscope was installed at the NSLS a few years later [10, 19]. Since then, IR microscopes have been installed on over 15 beamlines at synchrotrons worldwide, and an equal number are currently in the planning or construction stages. 

In reflection mode, the IR radiation reflects off of the sample and passes back through the illuminating objective. In this configuration, approximately 40-50% of the incident IR radiation is blocked by a mirror that collects the reflected light. This fraction can be reduced significantly with a synchrotron IR source. 

A considerable analytical effort has been expended recently on the chemical composition of human hair, for which the synchrotron IR source can provide the ability to probe, separately, the cuticle ( 5pm width), cortex (-40-80pm width) and medulla (-lOprn width) substructures (Figure 14.9) [70, 71]. The results of... 

Figure 14.9 Synchrotron IR images of the cross-section of a human hair. Hair contains three substructures that can only be resolved with the high spatial resolution of a synchrotron IR source. From the center outward, these substructures and their thicknesses are medulla (10-20nm), cortex...

Better resolution but stiU controlled by diffraction can be obtained with a synchrotron IR source in a confocal arrangement. The intrinsically brighter synchrotron IR source allows areas as small as 3-4 p,m to be probed [248-252, 266], which is very important for improving the quality of maps (vide infra). An additional advantage of synchrotron sources in orientational measurements is that the probing radiation is 100% polarized in the plane of the storage ring. 

To summarize, in this section we have shown how single-point microspectroscopy using the synchrotron IR source and small, confocal aperturing can deliver improved resolution and contrast for biological imaging when compared with various array detector microscopes using a thermal source, but these improvements come with a serious handicap - extremely long measurement times. 

Next, we report an example of a spectral image of an individual cell, which was grown onto a low-e slide as described above. We reported results from similar experiments before,14 which used a synchrotron light source and spectral mapping methodology. In these earlier experiments, we were able to achieve higher spatial resolution, due to the collimated nature of the IR beam from a synchrotron light... 

EXAFS data (Rh K-edge ((23220 eV) or Ir Lm-edge (13419 eV)) were collected in transmission mode on station 9.2 of the Daresbury Synchrotron Radiation Source, operating at 2 GeV with an average current of 150 mA. A water-cooled Si(220) double crystal monochromator was used, with its angle calibrated by running an edge scan of a 5 pm Rh or Ir foil. For each sample 2-10 scans were recorded at room temperature in the... 

Fig. 4. IR spectra of NO Os in the range 100-2500 cm measured at room temperature for five pressures (indicated in GPa on right hand ordinate). The absorbance has been normalized with respect to the beam current of the synchrotron light source. The sample thickness was about 23 pm. The region 1900-2200 cm is omitted because of interfering absorptions from the Type Ila diamonds used as anvils. Asterisks ( ) indicate lattice modes or combinations, (from Ref. [80])...

The IR spectra were recorded at ambient temperature (if not expressly stated otherwise) on a Fourier transform spectrometer DIGILAB FTS 20E with resolutions between 1 and 4 cnf . The EXAFS and XANES data were obtained at the Cu K edge on the E4 and X beam lines at the synchrotron radiation source of HASYLAB/DESY in Hamburg, at a ring energy of 5.3 GeV with a resolution of... 

Figure 2. Broadband spectrum of a conventional 2000 Globar IR source (short dashed line), and the spectrum of the NSLS synchrotron source (solid line) limited by an experimental throughput of...

Figure 3. Broadband spectrum of a conventional 2000 Globar IR source (short dashed line), and the spectrum of the NSLS synchrotron source (solid line) limited by an experimental throughput of 4.4><1 O 4 mm2sr. This is the etendue for a 1 pm by 1 pm sample measured with an infrared microscope. The measured, background limited Noise Equivalent Power (NEP) of a Mercury Cadmium Telluride (MCT) (long dashed line) detector is shown. This detector is operated at liquid nitrogen temperatures.

Figure 2. The distribution of CAL-B as function of matrix variables by IR microscopy. Synchrotron light source was only used on the images of 3(75 pm), 4(35 pm) and 5(35 pm). The number of samples is in corresponding to the number of entries in Table 1. (Reproducedfrom Langmuir 2007, 23, 6467-6474. Copyright 2007 American Chemical Society.)...

---