Contribution to the development of low frequency terahertz coherent Raman micro-spectroscopy and microscopy (original) (raw)
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Vibrational Spectroscopy, 2020
We report the extension of our formerly developed two-beam 3-color broadband coherent Raman methodology and the improvement of our tabletop system for fully polarization controlled low-frequency vibrational measurements. Each of the differently polarized partial signal in the coherent Raman scattering could be effectively eliminated at the theoretically predicted polarization analyzer orientations. The electronic contribution to the signal was suppressed without significantly reducing the vibrational contribution to the spectrum, which is a noteworthy advantage compared to Coherent anti-Stokes Raman Spectroscopy (CARS). The method was applied for well-characterized liquid CCl 4 and CHCl 3 samples for the first time. Coherent vibrational spectra were recorded simultaneously on the Stokes and anti-Stokes spectral-domain located near the zero frequency shift region. The methodology is easily extendable to measure vibrational or phonon spectra of anisotropic crystals.
Chemical Physics Letters, 2006
We have developed two bright hyper-Rayleigh/hyper-Raman spectrometers that allow the collection of spontaneous signals with high-quality and good spatial resolution. The first macro-spectrometer has been addressed to the study of liquids. The second is a new and original micro-spectrometer which has been designed to study solid and interface media. The micro-hyper-Raman spectrometer opens new fields of investigation since it provides vibrational informations, on IR-active but Raman-inactive modes, at the micrometer scale. Thus, the combination of Raman and hyper-Raman methods accomplishes high spatial resolution vibrational micro-spectroscopy.
Studies of minerals, organic and biogenic materials through timeresolved Raman spectroscopy
2009
A compact remote Raman spectroscopy system was developed at NASA Langley Research center and was previously demonstrated for its ability to identify chemical composition of various rocks and minerals. In this study, the Raman sensor was utilized to perform time-resolved Raman studies of various samples such as minerals and rocks, Azalea leaves and a few fossil samples. The Raman sensor utilizes a pulsed 532 nm Nd:YAG laser as excitation source, a 4-inch telescope to collect the Raman-scattered signal from a sample several meters away, a spectrograph equipped with a holographic grating, and a gated intensified CCD (ICCD) camera system. Time resolved Raman measurements were carried out by varying the gate delay with fixed short gate width of the ICCD camera, allowing measurement of both Raman signals and fluorescence signals. Rocks and mineral samples were characterized including marble, which contain CaCO 3 . Analysis of the results reveals the short (~10 -13 s) lifetime of the Raman process, and shows that Raman spectra of some mineral samples contain fluorescence emission due to organic impurities. Also analyzed were a green (pristine) and a yellow (decayed) sample of Gardenia leaves. It was observed that the fluorescence signals from the green and yellow leaf samples showed stronger signals compared to the Raman lines. Moreover, it was also observed that the fluorescence of the green leaf was more intense and had a shorter lifetime than that of the yellow leaf. For the fossil samples, Raman shifted lines could not be observed due the presence of very strong short-lived fluorescence.
A tool for assisting phase identification by micro‐Raman spectroscopy
Journal of Raman Spectroscopy, 2018
Although powder X‐ray diffraction is often the primary choice for the analysis of naturally occurring materials, the robust identification of individual components in a complex mixture is usually a challenging task, and other analytical tools are often needed to allow unequivocal phase identification. Among these techniques, the spatial resolution provided by micro‐Raman spectroscopy has proved to be invaluable as a complementary technique to X‐ray diffraction analysis. Accordingly, in this work we present a tool for assisting phase identification by micro‐Raman spectroscopy. This tool was implemented with a graphical user interface, thus facilitating all stages of analysis, including multiple spectra reading, interpolation, and baseline correction, as well as pure component spectra determination by multivariate curve resolution analysis and their identification against an open‐access database. To exemplify the proposed approach, the mineral phases present in an igneous rock from th...
Experimental aspects of Fourier transform Raman spectroscopy
Mikrochimica Acta, 1988
Using a commercial Fourier transform infrared spectrometer and the 1.064 #m line of a CW Nd : YAG laser, we have measured the Raman spectra of a wide variety of materials. The Raman scattered light, Stokes shifted toward the mid-infrared, is collected, using a 90 ~ lens geometry, and focused through the emission port of the spectrometer. After passing through the Michelson interferometer, the light is detected by a thermoelectrically-cooled high-sensitivity germanium detector. The Fourier transform of the resulting interferogram gives the Raman spectrum. This new technique allows spectra to be obtained of samples which were previously completely masked by competing fluorescence. In addition, FT-Raman also allows moieties, such as hydrocarbon chains, which are not present in resonance enhanced spectra, to be investigated. We will discuss our approach toward FT-Raman, which is compatible with traditional Raman spectroscopy, present representative spectra of liquids and solids, and draw some comparisons and contrasts between dispersive and FT measurements.
Raman spectroscopy at the beginning of the twenty-first century II
Journal of Raman Spectroscopy, 2008
This special issue of Journal of Raman Spectroscopy is published in honour of Professor Hiro-o Hamaguchi on the occasion of his 60 th birthday. The papers have been contributed by his colleagues who have had and continue to have the privilege of working with or alongside him. They highlight some of the areas in which Hiro-o has made significant contributions to vibrational spectroscopy, including timeresolved spectroscopy, instrument and technique development, microscopy and the application of Raman spectroscopy to probe biological systems.