Collection of scattered light

To increase the absorbance detection sensitivity, both a collimating lens and a detection slit have been used in a PDMS chip to reduce collection of scattered light [707], An improved S/N ratio was also obtained by using tapered channel waveguides as the collimators as well as the elliptical lens for absorbance detection [708],... 

Figure 13.4. Electrochemical cells for Raman spectroscopy based on (A) 180° geometry and (B) fiber-optic collection of scattered light.

Although Raman spectroscopy does not employ absorption of infrared radiation as its fundamental principle of operation, it is combined with other infrared spectroscopies into a joint section. Results obtained with various Raman spectroscopies as described below cover vibrational properties of molecules at interfaces complementing infrared spectroscopy in many cases. A general overview of applications of laser Raman spectroscopy (LRS) as applied to electrochemical interfaces has been provided [342]. Spatially offset Raman spectroscopy (SORS) enables spatially resolved Raman spectroscopic investigations of multilayered systems based on the collection of scattered light from spatial regions of the samples offset from the point of illumination [343]. So far this technique has only been applied in various fields outside electrochemistry [344]. Fourth-order coherent Raman spectroscopy has been developed and applied to solid/liquid interfaces [345] applications in electrochemical systems have not been reported so far. 

Fig. 3.5 Experimental arrangement for intracavity Raman spectroscopy with an argon laser CM, multiple reflection four-mirror system for efficient collection of scattered light LM, laser-resonator mirror DP, Dove prism, which turns the image of the horizontal interaction plane by 90° in order to match it to the vertical entrance slit S of the spectrograph FPE, Fabry-Perot etalon to enforce single-mode operation of the argon laser LP, Littrow prism for line selection [315]...

Fiber probes can also be used for directional/directional measurements. The illumination and collecting fibers may be concentric, mixed fiber bundles, half-moons, or other configurations. These allow the reflectance probes to be very small and efficient in the collection of scattered light. Many of the new NIR probes for quality control inspection of powders in situ employ this geometry. The primary disadvantage is that it is impossible... 

Figure 7. Optical confocal system for collection of scattering light from electrode surface.

At least two Raman spectroscopic methods are applicable in membrane surface characterization Fourier transform Raman spectroscopy (FT-Raman), and micro-Raman spectroscopy (Boccaccio et al., 2002 Gmger et al., 2001 Khulbe and Matsuura, 2000). In FT-Raman the sample molecules are excited with a near-infi ared (NIR) laser and appropriately configured Michelson interferometers, and Fomier transform processes are used in the collecting of scattered light and the analysis of the collected light. Almost the only requirement is that the sample to be analyzed with FT-Raman must not be black (Hendra, 2005). FT-Raman is a valuable tool in determining the overall chemical stmcture of a membrane, but it cannot characterize the asymmetric stmcture of a porous membrane matrix (Boccaccio et al., 2002). 

With the availability of lasers, Brillouin scattering can now be used more confidently to study electron-phonon interactions and to probe the energy, damping and relative weight of the various hydro-dynamic collective modes in anharmonic insulating crystals.The connection between the intensity and spectral distribution of scattered light and the nuclear displacement-displacement correlation function has been extensively discussed by Griffin 236). 

Yan et al. [71] have used a hollow photonic crystal fiber bundle to immobilize multifaceted AuNPs of 100-200 nm diameters within the hollow stmcture (Fig. 12). They launched the excitation light at 633 nm for Raman spectroscopy onto the end fire of the photonic crystal fiber with a x50 objective. The same objective lens was used to collect the scattered light for Raman spectroscopy. The sensing material or analyte was rhodamine B immobihzed and dried within the photonic fiber onto the AuNPs. The Raman spectrum showed a clear surface enhancement in the presence of the AuNPs. Nevertheless the authors used a photonic crystal fiber, no band gap... 

Monochromatic light (in the visible or uv range) is directed through the sample (gas, liquid, crystal, or powder), which must be translucent. Light scattered at 90° or 180° is collected, analyzed, and recorded. The incident light commonly used in modern instruments is from a laser source and may be polarized. The Raman effect involves shifts of frequency of scattered light relative to that from the source... 

A simple light scattering photometer was designed, to measure the angular distribution of intensity of scattered, polarized, He/Ne light, by micron and sub-micron particles [186]. The photometer used an ellipsoidal reflector and simple optical components to collect the scattered light and focus it on a 512 element photodiode array. 

Leeds and Northrup Microtrac Ultrafme Particle Analyzer (VPA) uses the controlled reference method, using a sapphire tipped waveguide that collects back-scattered light within 100 pm of probe tip, to cover the size range 0.003 to 6.5 pm. 

While commercial Raman spectrometers collect the scattered light from a laser spot of size 1 pm at best and the Raman spectra also include information of sample regions above and below the focal plane, the implementation of confocal microscopy can improve the optical resolution and the depth of sharpness. The method leads to better image definition. Confocal microscopy means point illumination and that a small aperture is placed in the optical path so that only the scattered light located in a thin focus plane can reach the detector. The aperture-dependent spatial... 

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