Laser raman microspectroscopy

Parkinson C. D. and Katayama 1. (1999) Present-day ultrahigh-pressure conditions of coesite inclusions in zircon and garnet evidence from laser Raman microspectroscopy. Geology 27, 979-982. 

Laser Raman microspectroscopy is unique among these techniques in that it is nondestructive. This method was first attempted on fluid inclusions by Rosasco Roedder (1979), and has been used by several researchers on a variety of fluid inclusions. This method involves focusing a non-destructive laser microprobe on a single fluid inclusion. A very small portion of the energy from the laser excites covalent bonds, causing vibrations due to stretching or bending of the bond. Therefore, only covalently bonded species can be identified such as sulfate, or bicarbonate. This method has been used to determine the pH of fluid inclusions in Permian lacustrine halite from Kansas (Benison et al., 1998). 

Laser raman microspectroscopy Involves the use of a laser, which excites the covalent bonds of complexes. Can be used to identify various covalently bonded ionic complexes in fluid inclusions. 

Wang, C. et al. (2009) Confocal laser Raman microspectroscopy of biomineralization foci in UMR 106 osteoblastic cultures reveals temporally synchronized protein changes preceding... 

Abstract world class unconformity-related U deposits occur in the Proterozoic McArthur Basin (Northern Territory, Australia) and Athabasca Basin (Saskatchewan, Canada). Widespread pre-to post-ore silicifications in the vicinity of the deposits, allow proper observation of paragenetically well-characterized fluid inclusions. We used a combination of microthermometry, Raman microspectroscopy and Laser Induced Breakdown Spectroscopy (LIBS), to establish the physical-chemical characteristics of the main fluids having circulated at the time of U mineralization. The deduced salinities, cation ratios (Na/Ca, Na/Mg) and P-T conditions, led to the detailed characterization of a NaCI-rich brine, a CaCl2-rich brine and a low-salinity fluid, and to the identification of mixing processes that appear to be key factors for U mineralization. 

Written by an international panel of experts, this volume begins with a comparison of nonlinear optical spectroscopy and x-ray crystallography. The text examines the use of multiphoton fluorescence to study chemical phenomena in the skin, the use of nonlinear optics to enhance traditional optical spectroscopy, and the multimodal approach, which incorporates several spectroscopic techniques in one instrument. Later chapters explore Raman microscopy, third-harmonic generation microscopy, and nonlinear Raman microspectroscopy. The text explores the promise of beam shaping and the use of a broadband laser pulse generated through continuum generation and an optical pulse shaper. 

Similar approaches were adopted by Ganikhanov (Chapter 5), who developed a state-of-the-art laser system, benefiting simultaneous third-harmonic and nonlinear Raman microscopy, and Yakovlev et al. (Chapter 6), who applied third-harmonic generation microscopy and nonlinear Raman microspectroscopy for biochemical analysis in microfluidic devices. 

Raman microscopes are more commonly used for materials characterization than other Raman instruments. Raman microscopes are able to examine microscopic areas of materials by focusing the laser beam down to the micrometer level without much sample preparation as long as a surface of the sample is free from contamination. This technique should be referred to as Raman microspectroscopy because Raman microscopy is not mainly used for imaging purposes, similar to FUR microspectroscopy. An important difference between Raman micro-and FUR microspectroscopies is their spatial resolution. The spatial resolution of the Raman microscope is at least one order of magnitude higher than the FTIR microscope. 

In principle, Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength, which is about 10-fold smaller for Raman spectroscopy with a visible laser than for mid-lR spectroscopy. It is therefore possible to focus visible or NIR laser light to much smaller spot... 

Raman microspectroscopy was not a completely new concept. In 1966, Delhaye and Migeon [35] showed that a laser beam could be hghtly focused at a sample, and that Raman-scattered light could be collected and transferred to a spectrometer, with minimal loss. Their calculahons showed that the increased irradiance more than compensated for the decrease in the size of the irradiated volume. The first Raman microscope was reported by Delhaye and Dhamelincourt in 1975 [36], and an instrument based on these principles (the MOLE) was introduced by Jobin Yvon at about the same time. However, the optical scheme used for imaging, which employed global illumination, was inefHcient and it was not until the advent of CCD-Raman spectrometers that the advantages of Raman microscopy became apparent. 

Structural investigations in laser-assisted chemical vapor-deposited boron carbide thin films by Raman microspectroscopy and glancing incidence XRD, have provided... 

In principle, Raman spectroscopy is a microtechnique [161) since, for a given light flux of a laser source, the flux of Raman radiation is inversely proportional to the diameter of the laser-beam focus at the sample, i.e., an optimized Raman sample is a microsample. However, Raman microspectroscopy able to obtain spatially resolved vibrational spectra to ca. 1 pm spatial resolution and using a conventional optical microscope system has only recently been more widely appreciated. For Raman microspectroscopy both conventional [162] and FT-Raman spectrometers [ 163], [ 164] are employed, the latter being coupled by near-infrared fiber optics to the microscope. 

Raman microspectroscopy provides a detailed view of the three-dimensional arrangement of the molecules inside the LC droplets. Because it proves the interaction of individual bond vibrations with laser light, the method allows the mapping of segregation as a function of chemical composition. The quantitative imaging of Raman intensity reveals information about the spatial organization of the molecules and their local environment. Thus, the method maps the director fields of the liquid crystal molecules in the horizontal plane and in the vertical direction (Blach et al. 2005). 

Table 5.50 lists the main features of Raman microspectroscopy. Virtually any object which can be observed under a microscope can be analysed with Raman microscopy. Here, the usual constraints inherent in electron beam methods (vacuum, metallisation, etc.) are totally absent. Although micro-Raman spectrometers mainly use visible excitation, the confocal configuration almost eliminates fluorescence which falls outside of the focal volume. The focus area for visible lasers is <1 /xm, whereas the focus diameter for NIR lasers is 20 fim. 

The future of Raman microspectroscopy is probably imaging and optical near-field nano-Raman spectroscopy [529], cfr. Chp. 5.5.2. While conventional laser Raman spectroscopy samples 10 g (mm ), /zRS handles 10 g (nm ) and near-field Raman spectroscopy 10 g (nm ). Mobile Raman microscopy (MRM) allows in situ Raman analysis [530]. One can expect further developments in the field of NIR multichannel Raman spectroscopy with the advent of 2D array detectors offering extended response in the NIR. With these 2D sensors it wiU become possible to apply in the NIR region the powerful techniques already developed in the visible, such as confocal line imaging techniques or multisite remote analysis with optical fibres. 

Raman microspectroscopy. It must be noted that with modern micro-Raman systems, live or fixed cells can now easily be probed with green lasers operating at low powers without damaging them and with little or no parasitic fluorescence background. 

In principle, Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength, which is about 10-fold smaller for Raman spectroscopy with a visible laser than for mid-IR spectroscopy. It is therefore possible to focus visible laser light to much smaller spot sizes (400 nm in air and 240 nm with an oil immersion objective) than may be examined by mid-IR radiation. For various instrument-based reasons [4], charge-coupled device (CCD) Raman spectrometers have in practice proved to be far more successful for Raman microspectroscopy than ET-Raman spectrometers, and most instruments are based on this former concept. One further important instrumental advantage of the microscopes used for Raman microspectroscopy is their confocal design [5]. As the out-of-focus rays from an illuminated volume... 

Arguably the most important advantage of many microscopes used for Raman microspectroscopy is the fact that they have a confocal design. In a typical confo-cal design, see Figure 1.9, the laser beam is focused on a small aperture (to clean... 

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