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Laser scattering diagnostics

One of the earliest detailed diagnostic efforts on sooting of diffusion flames was that of Wagner et al. [86-88], who made laser scattering and extinction measurements, profile determinations of velocity by LDV, and temperature measurements by thermocouples on a Wolfhard-Parker burner using ethene as the fuel. Their results show quite clearly that soot particles are generated near the reaction zone and are convected farther toward the center of the fuel stream as they travel up the flame. The particle number densities and generation rates decline with distance from the flame zone. The soot formation rate appeared to... [Pg.476]

Figure 5. Current overall optical layout for laser velocimetry and Raman scattering diagnostics, shown here on new fan-induced square-cross-section movable combustion tunnel. Note the co-linear Raman and LV probe laser source axes and the colinear detection optics. Figure 5. Current overall optical layout for laser velocimetry and Raman scattering diagnostics, shown here on new fan-induced square-cross-section movable combustion tunnel. Note the co-linear Raman and LV probe laser source axes and the colinear detection optics.
A Nd YAG Laser Multipass Cell for Pulsed Raman-Scattering Diagnostics... [Pg.255]

The various techniques of Raman scattering that enable laser-based diagnostics of technical combustion processes as well as species identification on the micrometer scale or remote sensing of molecular species and pollutant in the atmosphere. [Pg.2455]

The laser combustion diagnostics techniques discussed so far utilized resonant processes, whether it be single- or multi-photon excitation, fluorescence or stimulated emission. We will now consider non-resonant processes of Raman nature. Because of its msensitivity to quenching (the lifetime of the virtual state is lO s), Raman spectroscopy is of considerable interest for quantitative measurements on combustion processes. Further, important flame species such as O2, N2 and H2 that do not exhibit IR transitions (Sect. 4.2.2) can be readily studied with the Raman technique. However, because of the inherent weakness of the Raman scattering process (Sect. 4.3) only non-luminous (non-sooting) flames can be studied. [Pg.398]

Raman spectroscopy is primarily useful as a diagnostic, inasmuch as the vibrational Raman spectrum is directly related to molecular structure and bonding. The major development since 1965 in spontaneous, c.w. Raman spectroscopy has been the observation and exploitation by chemists of the resonance Raman effect. This advance, pioneered in chemical applications by Long and Loehr (15a) and by Spiro and Strekas (15b), overcomes the inherently feeble nature of normal (nonresonant) Raman scattering and allows observation of Raman spectra of dilute chemical systems. Because the observation of the resonance effect requires selection of a laser wavelength at or near an electronic transition of the sample, developments in resonance Raman spectroscopy have closely paralleled the increasing availability of widely tunable and line-selectable lasers. [Pg.466]

Laser-based spectroscopic probes promise a wealth of detailed data--concentrations and temperatures of specific individual molecules under high spatial resolution--necessary to understand the chemistry of combustion. Of the probe techniques, the methods of spontaneous and coherent Raman scattering for major species, and laser-induced fluorescence for minor species, form attractive complements. Computational developments now permit realistic and detailed simulation models of combustion systems advances in combustion will result from a combination of these laser probes and computer models. Finally, the close coupling between current research in other areas of physical chemistry and the development of laser diagnostics is illustrated by recent LIF experiments on OH in flames. [Pg.17]

The fundamentals of the Raman effect can be understood by consideration of a classical model, in which an incident beam of radiation (i.e., laser beam, for all practical purposes, in flame diagnostics) passes through an ensemble of molecules. The resultant laser beam electric field distorts the electronic cloud distribution of each molecule, causing oscillating dipoles these induced dipoles are related to the incident laser beam electric field by the molecular polarizability. The dipoles, in turn, produce a secondary radiating field at essentially the same frequency as that for the incident beam. This radiation is termed Rayleigh scattering. [Pg.212]

During the last 25 years X-ray spectroscopy has been intensively developed for plasma diagnostics. Since the first application of X-ray spectrometers on the early fusion devices such as PLT and TFR, it has been used to determine basic plasma parameters such as the temperature of ions and electrons. It is now frequently being applied not only to low density plasmas in tokamaks and astrophysical objects [1], but also to laser-produced plasma [2]. It has been shown, that the precision of plasma parameters as obtained from X-ray spectroscopy is competitive to the standard methods for plasma diagnostics, such as Thomson scattering and charge exchange spectroscopy for electron and ion temperature, respectively [3]. [Pg.183]

Because the level of received black-body emission is comparable to that of the laser, special attention needs to be given to the elimination of this emission in optical diagnostics. For example, in scattering and extinction experiments, narrow-bandpass filters, combined with slits and shields and/or lock-in amplifiers with chopped signals, are common practices. ... [Pg.421]

Particle sizing is not only peculiar to the scattering of light. It can also be achieved by means of LII in the context of soot diagnostic [9]. The idea is to heat the soot particles with a powerful laser pulse. After the absorption, the particles start to radiate the excess of thermal energy that is measured as a temporal decay informative of the particle size. [Pg.281]


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