Raman response

Tokmakoff A, Lang M J, Larson D S and Fleming G R 1997 Intrinsic optical heterodyne detection of a two-dimensional fifth order Raman response Chem. Phys. Lett. 272 48-54... 

Raman scattering is a linear spectroscopy, in principle, meaning that the Raman scattering intensity, 7S, scales linearly with the intensity of the incident light, IL, provided the scattering compound can be considered as optically thin. At fixed incident light intensity IL, the Raman response scales with the population density of the scatterers, N(E) according to... 

Here, oR is the Raman cross section, a constant whose magnitude depends on the excitation and collection geometry. In optically thick media, as in a geometrically thin but optically dense tissue, a deviation from the linear Raman response of Is versus concentration N is to be expected. This can... 

Ward DR, Halas NJ, Ciszek JW, Tour JM, Wu Y, Nordlander P, Natelson D (2008) Simultaneous measurements of electronic conduction and Raman response in molecular junctions. Nano Lett 8(3) 919-924... 

As illustrated earlier in the text (Figure 10.5), molecules released from the centrifuge generate an oscillatory Raman signal, characteristic of the coherent rotation with well-defined relative phase relation between the quantum states inside a rotational wave packet. Time-resolved coherent Raman response from a wave packet centered at A = 69 in oxygen is plotted at the bottom of Figure 10.9a. Knowing the wave packet composition from the state-resolved detection discussed above. 

Fig. 2. Fleterodyne detected fifth-order Raman response of liquid CS2 for two different polarization conditions (A) Rnnn and (B, C) the Dutch Cross , Rl-liill, configuration. The solid curves are the in-phase signals, and the dashed lines are the 7t/2 shifted signals (not discussed). Panels B, and C show slices along Z and the diagonal. L = 60°...

The Raman effect has also been broadly applied to online and bench-top quantitative applications, such as determination of pharmaceutical materials and process monitoring [4-6], in vivo clinical measurements [7], biological materials [8, 9], to name only a few. Because the absolute Raman response is difficult to measure accurately (sample presentation and delivered laser power can vary), these measurements are almost always calculated as a percentage with respect to the response from an internal standard. This standard is typically part of the sample matrix in a drug product, the standard may be an excipient in a biological sample, it is commonly water. 

Fig. 6.8. A Principle of frequency-multiplexed CARS microspectroscopy A narrow-bandwidth pump pulse determines the inherent spectral resolution, while a broad-bandwidth Stokes pulse allows simultaneous detection over a wide range of Raman shifts. The multiplex CARS spectra shown originate from a 70 mM solution of cholesterol in CCI4 (solid line) and the nonresonant background of coverglass (dashed line) at a Raman shift centered at 2900 cm-1. B Energy level diagram for a multiplex CARS process. C Schematic of the multiplex CARS microscope (P polarizer HWP/QWP half/quarter-wave plate BC dichroic beam combiner Obj objective lens F filter A analyzer FM flip mirror L lens D detector S sample). D Measured normalized CARS spectrum of the cholesterol solution. E Maximum entropy method (MEM) phase spectrum (solid line) retrieved from (D) and the error background phase (dashed line) determined by a polynomial fit to those spectral regions without vibrational resonances. F Retrieved Raman response (solid line) calculated from the spectra shown in (E), directly reproducing the independently measured spontaneous Raman response (dashed line) of the same cholesterol sample...

Analogous to the principal concept of multiplex CARS microspectroscopy (cf. Sect. 6.3.5), in multiplex SRS detection a pair of a broad-bandwidth pulse, eg., white-light femtosecond pulse, and a narrow-bandwidth picosecond pulse that determine the spectral width of the SRS spectrum and its inherent spectral resolution, respectively, is used to simultaneously excite multiple Raman resonances in the sample. Due to SRS, modulations appear in the spectrum of the transmitted broad-bandwidth pulse, which are read out using a photodiode array detector. Unlike SRS imaging, it is difficult to integrate phase-sensitive lock-in detection with a multiplex detector in order to directly retrieve the Raman spectrum from these modulations. Instead, two consecutive spectra, i.e., one with the narrow-bandwidth picosecond beam present and one with that beam blocked, are recorded. Their ratio allows the computation of the linear Raman spectrum that can readily be interpreted in a quantitative manner [49]. Unlike the spectral analysis of a multiplex CARS spectrum, no retrieval of hidden phase information is required to obtain the spontaneous Raman response in multiplex SRS microspectroscopy. 

Fig. 12.2. In vitro Raman spectrum of the nucleus of a 23-year-old human intact lens, showing Raman responses from protein components and water in the 500-4000 cm-1 region. Adapted from [5]...

Fig. 12.7. Analysis of Raman spectra obtained in vitro for Bruch s membrane, showing component spectra (a) and (b) for heme and collagen, respectively, and a residual spectrum (c) assigned to Raman responses of age-related glycation end products and proteins. Adapted from [29]...

Fig. 12.14. Resonance Raman imaging results for the macular pigment distribution in the retina of a volunteer subject, a Typical gray-scale image obtained after subtraction of fluorescence background from pixel intensity map containing Raman response and superimposed fluorescence background, b Gray-scaled, three-dimensional representation of gray-scale image...

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