Time-resolved spectroscopic imaging

Xe Ice Melting Process. - The melting and dissolution processes of xenon (Xe) ice into different solvents have been visualized, using the methods of NMR spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized Starting from the initial condition of a hyperpolarized... 

There are several future directions that NIR brain sensing and imaging research can take. In instrumentation, advances in time-resolve spectroscopic equipment may yield less expensive equipment and thus a more prolific use. This will allow for approximation of time of flight parameter providing a possible avenue for inferring path length. Theoretically, there is a need for better theoretical modeling to eliminate crosstalk noise. Possible improvements have already been introduced by Boas, et. al [8]. However, more human subject studies need to be conducted to... 

Lukins, P.B., Rehman, S., Stevens, G.B. and George, D. (2005) Time-resolved spectroscopic fluorescence imaging, transient absorption and vibrational... 

Nanosecond time-resolved crystallography of MbCO has been discussed in Section 3.7.2.3 of Chapter 3.46 After firing a 10-ns burst of laser light to break the CO-Fe bond, these researchers produced a diffraction image of the crystal through application of a 150-ps X-ray pulse. They are able to show release of the CO molecule, displacement of the Fe ion toward the proximal histidine, and recombination of the dissociated CO by about 100 ps. Essentially their results compare well with other spectroscopic studies of HbCO, MbCO and their models. 

This paper presents an overview of the current research issues and commercialization efforts related to laser ablation for chemical analysis, discusses several fundamental studies of laser ablation using time-resolved shadowgraph and spectroscopic imaging, and describes recent data using nanosecond laser pulsed ablation sampling for ICP-MS and LIBS. Efforts towards commercialization of field based LIBS systems also will be described. 

However, atom motions cannot be unambiguously imaged by time-resolved optical spectroscopic methods as they do not directly measure the structural dynamics but instead characterize energetic properties. Consequently, novel methods that enable the direct measurement of molecular motions during chemical processes are needed. Furthermore, chemical reactions often occur in solution and, consequently, it is desirable that such methods are applicable to chemical processes in the liquid phase. 

Beyond imaging, the combination of CRS microscopy with spectroscopic techniques has been used to obtain the full wealth of the chemical and the physical structure information of submicron-sized samples. In the frequency domain, multiplex CRS microspectroscopy allows the chemical identification of molecules on the basis of their characteristic Raman spectra and the extraction of their physical properties, e.g., their thermodynamic state. In the time domain, time-resolved CRS microscopy allows the recording of the localized Raman free induction decay occurring on the femtosecond and picosecond time scales. CRS correlation spectroscopy can probe three-dimensional diffusion dynamics with chemical selectivity. 

Infrared microspectroscopy has been reviewed [436,444 47] and theory and applications have been described in several recent books [393,417-419], An introduction to step-scan FTIR is available [448]. The role of IR and Raman microscopy/ microprobe spectroscopic techniques in the characterisation of polymers, their products, and composites was reviewed [449]. McClure [450] has described NIR imaging spectroscopy and a recent review on time-resolved studies of polymers by mid-and near-infrared spectroscopy has appeared [451]. Near-infrared microspectroscopy and its applications have been reviewed [452]. 

This time-resolved measurement method can be applicable to relatively slow transient phenomena, as its time-resolved measurements are undertaken while the movable mirror is at rest. The number of applications of step-scan FT-IR spectrometry to time-resolved measurements currently is more than that by any other method, and it has been applied to various studies in many fields such as studies of biomolecules, liquid crystals, polymers, photochemical reactions in zeolites, oxidation-reduction reactions on electrode surfaces, and excited electronic states of inorganic complexes. Further, this method has been applied to time-resolved measurements in combination with attenuated total reflection (ATR) (see Chapter 13), surface-enhanced infrared absorption (see Section 13.2.2) [10, 11], infrared microscopic measurements (see Chapter 16) [12], and infrared spectroscopic imaging (see Chapter 17) [13]. 

Bhargava, R. and Levin, I.W. (2003) Time-resolved Eourier transform infrared spectroscopic imaging. Appl. Spectrosc., 57, 357-366. 

PA and PT phenomena are widely used for numerous non-spectroscopic applications such as the determination of thermal diffusivity, non-destructive testing of materials (in particular the probing of sub-surface defects) by thermal wave imaging, time-resolved studies of de-excitation processes or on biological photoreceptors, studies of phase transitions, etc. Here, only spectroscopic applications are considered that demonstrate the main characteristics and the potential of photoacoustic spectroscopy (PAS). In the following, illustrative examples are presented for solids, liquids, gases, biological and medical samples. 

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