Laser based method

A method which competes with interferometric distance measurement is laser Doppler displacement. In this approach the Doppler shift of the beam reflected from a target is measured and integrated to obtain displacement. This method also is best suited to use indoors at distances no more than a few hundred meters. Table 2 compares some of the characteristics of these laser-based methods of distance measurement. 

Laser-based methods of identification are extremely powerful they are able to provide species and structural information, as well as accurate system temperature values. Spontaneous Raman scattering experiments are useful for detection of the major species present in the system. Raman scattering is the result of an inelastic collision process between the photons and the molecule, allowing light to excite the molecule into a virtual state. The scattered light is either weaker (Stokes shifted) or... 

Various techniques have been introduced which still lack specific applications in polymer/additive analysis, but which may reasonably be expected to lead to significant contributions in the future. Examples are LC-QToFMS, LC-multi-API-MS, GC-ToFMS, Raman spectroscopy (to a minor extent), etc. Expectations for DIP-ToFMS [132], PTV-GC-ToFMS [133] and ASE are high. The advantages of SFC [134,135], on-line multidimensional chromatographic techniques [136,137] and laser-based methods for polymer/additive analysis appear to be more distant. Table 10.33 lists some innovative polymer/additive analysis protocols. As in all endeavours, the introduction of new technology needs a champion. 

Other laser-based methods for explosive detection. 299... 

In addition to the IR, Raman and LIBS methods previously discussed, a number of other laser-based methods for explosives detection have been developed over the years. The following section briefly describes the ultraviolet and visible (UV/vis) absorption spectra of EM and discusses the techniques of laser desorption (LD), PF with detection through resonance-enhanced multiphoton ionization (REMPI) or laser-induced fluorescence (LIF), photoacoustic spectroscopy (PAS), variations on the light ranging and detecting (LIDAR) method, and photoluminescence. Table 2 summarizes the LODs of several explosive-related compounds (ERC) and EM obtained by the techniques described in this section. 

The central idea in the laser-based method for detection of small quantities of H in restricted areas is that an intense laser strike can form a pothole in a metal. The metal of the pothole and the H it contains are vaporized. Both the H and some of the metallic atoms are withdrawn by a vacuum that pulls gaseous constituents out of the system. On the way, however, these constituents are made to fly through the space between the electrodes of a quadrupole mass spectrometer set to measure mass 2. Knowing the H2 produced from one laser strike, and the dimensions of the pothole, the H concentration in the metal—and within any restricted area to which the laser can be directed—can be measured. 

In the case of atomic absorption and atomic fluorescence the selectivity is thus already partly realized by the radiation source delivering the primary radiation, which in most cases is a line source (hollow cathode lamp, laser, etc.). Therefore, the spectral bandpass of the monochromator is not as critical as it is in atomic emission work. This is especially true for laser based methods, where in some cases of atomic fluorescence a filter is sufficient, or for laser induced ionization spectrometry where no spectral isolation is required at all. 

Laser ablation has grown to be an important technique for the fabrication of microelements. The role of microtechnology will increase in the coming years and laser-based fabrication processes are one of the key technologies for the future. The application of designed materials, especially polymers, will further improve the performance of laser-based methods. Already companies are specialized and offer polymers designed for laser structuring. 

Figure 9. Oxygen isotope compositions of nominally fresh MORE glasses and whole-rocks. Unfilled boxes are data collected using conventional (resistance heated) fluorination methods between 1966 and 1993 filled boxes are data collected only on glass using laser-based methods. Where these two data types overlap, conventional fluorination data are shown as white-outlined boxes. Data sources Taylor (1968), Muehlenbachs and Clayton (1972), Pineau et al. (1976), Kyser et al. (1982), Muehlenbachs and Byerly (1982), Ito et al. (1987), Barrat et al. (1993), Harmon and Hoefs (1995) and references therein, Eiler et al. (2000b), and Eiler and Kitchen (unpublished data).

Continental flood basalts. A first-pass has been made at applying laser-based methods to study the oxygen isotope systematics of most major classes of terrestrial basalts. However, continental flood basalts are an exception and the one detailed study that has been made (Baker et al. 2000) suggests that much will be learned by such work. 

An infrared laser-based method for investigating the nascent state distribution of the reaction products HF from the reaction F - - H2 HF -I- H in crossed molecular beams under single collision conditions has been presented by the group of D.J. Nesbit [1061]. The experimental setup (Fig. 8.24) consisted of a pulsed supersonic discharge source of F atoms, which collide with H2 molecules in a second pulsed jet source. The product HF(v, J) is probed in the intersection region by the absorption of a single-mode tunable IR laser, where full vibrationn-otation resolution can be achieved (Fig. 8.25). 

The laser-based methods make use of different types of laser sources. Many of them, such as the solid-state laser or the semiconductor laser, are under continuous development because of the discovery of new lasing materials or the optimization of frequency conversion techniques. The type of the analytical application and the nature of the required information determine the choice of a special laser source, particularly pulsed or continuous-wave (CW) operating mode. Pulsed laser sources with fixed wavelength are usually used for LA, whereas both tunable pulsed and CW laser sources are preferred for element-specific detection or plasma diagnostics. 

Tittel FK (1999) Detectirai of trace gas contaminants using diode laser based methods. In Lasers and electro-optics. CLEO/Pacific Rim 99. The Pacific Rim conference on lasers and electo-optics, IEEE, Seoul... 

The other chief comptment of a mass spectrometer, the ion source, determines the types of ions that can be examined when starting fi om a specific sample (Gross and Caprioli, 2007). Laser-based methods, variably dubbed ablation, ionization, and desorption/ionization supposedly depending on the involved laser power, have played an important role fi om initial studies of bare metal ions to the widespread sought-after production of cluster ions for these latter species, the development of the so-called cluster sources was key to progress (Duncan, 2012). In more recent years, electrospray ionization (ESI) has played a central role due to its capacity to transfer/produce ions from solutions under mild conditions. Besides yielding new types of ions for chemical probing, ESI became a method of choice for the identification of solution species (speciation) and for direct observation of reaction... 

In concluding this section, we emphasize that we have selected a few of the techniques and spectroscopic applications out of the multitude of methods which now comprise the experimental field of laser spectroscopy. The choice of laser based methods for description is biased by their general applicabihty to the subject of interest in this series of handbook volumes which is the elucidation of the physical and chemical properties of lanthanide systems. 

The phase Doppler Technique is a laser-based interferometric approach for simultaneously measuring particle size and velocity. This laser-based method is similar to the well-known laser Doppler velocimeter (LDV) and can make these measurements non-intrusively and with high accuracy. The Phase Doppler Particle Analyzer (PDPA) has been successful applied to many difilcult two-phase flow environments with spherical particles including gas-turbine and rocket fuel inlection, cavitation and bubble formation, and similar two-phase flows. ... 

The laser-based methods discussed thus far can be used to probe surface and interstitial contaminants as well as for the direct determination of additives in a complex matrix. It is now common to have a CCD camera and video display that gives a microscopic view of the sample when it is in the mass spectrometer. This allows contaminants, defects, and areas of interest to be observed and manipulated while under the probing beW of the laser (25). A number of industrial examples have I ved that direct Laser Probe FT/MS analyses can rapidly determine many additives directly, even when the combination of laborious classical wet chemical techniques with other modem instrumental methods have proved difficult and time consuming. 

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