Laser Methods

Laser methods have been used to study the composition of occlusions in metals, variations in surface concentration of metals, and small areas of biological samples. 

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For the analysis of the chemical structure of flames, laser methods will typically provide temperature measurement and concentration profiles of some readily detectable radicals. The following two examples compare selected LIF and CRDS results. Figure 2.1 presents the temperature profile in a fuel-rich (C/O = 0.6) propene-oxygen-argon flame at 50 mbar [42]. For the LIF measurements, 1% NO was added. OH-LIF thermometry would also be possible, but regarding the rather low OH concentrations in fuel-rich flames, especially at low temperatures, this approach does not capture the temperature rise in the flame front [43]. The sensitivity of the CRDS technique, however, is superior, and the OH mole fraction is sufficient to follow the entire temperature profile. Both measurements are in excellent agreement. For all flames studied here, the temperature profile has been measured by LIF and/or CRDS. 

A technique which is not a laser method but which is most useful when combined with laser spectroscopy (LA/LIF) is that of supersonic molecular beams (27). If a molecule can be coaxed into the gas phase, it can be expanded through a supersonic nozzle at fairly high flux into a supersonic beam. The apparatus for this is fairly simple, in molecular beam terms. The result of the supersonic expansion is to cool the molecules rotationally to a few degrees Kelvin and vibrationally to a few tens of degrees, eliminating almost all thermal population of vibrational and rotational states and enormously simplifying the LA/LIF spectra that are observed. It is then possible, even for complex molecules, to make reliable vibronic assignments and infer structural parameters of the unperturbed molecule therefrom. Molecules as complex as metal phthalocyanines have been examined by this technique. 

For samples with low values of K, < 500 ppm, the laser method, because of its small sample size, becomes more uncertain than a thermal release study with a larger sample size. It is not possible to compensate in the laser probe method by multiple pulses above MOO individual pulses which corresponds to evaporation of approximately 20 pg. It is conceivable that by completely redesigning a mass spectrometer with smaller volumes which is bakeable to higher temperatures to alleviate this problem. We have been able on occasion to work with samples as low as 100 ppm K but certainly not on a routine basis. 

The time of crystallization of a lunar "granite" has also been determined by the laser method. This "granite" is the K- and Si-rich felsite that forms clasts in 73215, 73255, and Boulder 1 at Station 2. The laser results set a lower limit of 4.00 G.y. on crystallization of the parent body of this felsite, and the Rb-Sr data set an upper limit of 4.05 G.y. [6]. 

Intramolecular charge transfer in p-anthracene-(CH2)3-p-Ar,Af-dimethylaniline (61) has been observed174 in non-polar solvents. Measurements of fluorescence-decay (by the picosecond laser method) allow some conclusions about charge-transfer dynamics in solution internal rotation is required to reach a favourable geometry for the formation of intramolecular charge-transfer between the donor (aniline) and the acceptor (anthracene). 

Pulse radiolysis and pulsed laser methods are powerful tools to study the reactions at the interface between clusters and solution, such as fast heterogeneous catalytic processes, or transfer of the charges generated inside the particle. 

Colbert, J.C. (Ed.), Modem Coating Technology, Radiation Curing, Electrostatic, Plasma and Laser Methods, Noyes Data Corporation, Park Ridge, NJ (1982). 

If very hard materials (e.g., natural stone, or metal sheets) must be cut, the injection of abrasives into the water jet will support and accelerate the cutting procedure (see Fig. 1.4-5, bottom, right side). The water-jet cutting represents a very flexible production method which can be regarded as supplementary to LASER methods if thermal influences on the materials involved cannot be accepted. 

A laser method which has been used to study autoionizing states of alkaline earth atoms is the isolated core excitation (ICE) method first used by Cooke etal. to study the autoionizing 5pn( states of Sr.11 It has since been used to study autoionizing states of Mg, Ca, and Ba as well.12-14... 

Lanthanide triflates, for allylic tin reactions, 9, 354 Laser beam heating, in metal vapor synthesis, 1, 224 Laser methods, in mechanistic studies, 1, 248 Laser photochemical vapor deposition, with organometallic complexes, 1, 259... 

A succinct summary of the capabilities of the site selective laser methods is given below. 

Recently, there have appeared two important new technological advances, which make possible this kind of detailed, fundamental approach. Laser methods enable us to measure species concentrations and temperatures for a wide variety of molecules over a range of conditions, and to do so with high spatial resolution. Large scale computational techniques permit the formulation of realistic simulation models of the combustion system, including... 

Strain of small diameter fibers can be determined at room temperature using noncontact laser methods.56 While the technique yields good results at room temperature, it is not clear that it is readily adaptable to higher temperatures without significant modifications in coupling fluid, and mounting methods and materials. 

The laser method is also the least expensive method yet developed for making thin superconducting films. Cost savings, then, may become more substantial later on, said Venkatesan, because the pulsed method lends itself to mass production. The lasers we ve been using are very low power, compared to what else is out there. With larger, more powerful lasers, thin films can be deposited over larger areas in even shorter amounts of time. ... 

Narayan, J., Godbole, V.P., and White, G.W. (1991) Laser Method for Synthesis and Processing of Continuous Diamond Films on Nondiamond Substrates, Science, Vol. 52, pp. 416-418. 

Analysis of the literature reveals no significant differences between electrocoagulation and (very expensive) laser treatment procedures in terms of primary or definitive haemostasis. With laser therapy, the complication rate (0—4%) lies above that of electrocoagulation (0%). Heat and bipolar probes may be regarded as the most tissue-friendly , an inference supported by the results of animal experiments, while laser and monopolar probe methods are more aggressive . The electrohydrothermal probe offers a compromise. An additional consideration is that electrocoagulation and EHT procedures are technically uncomplicated, locally applicable and lower in cost compared to laser methods. 

The characterization and quality control of the particle size distribution of the discharged aerosol has become one of the key tests applied to MDI and other inhaler products, and a wide variety of methods have been developed to make this possible. The available methods can be broadly split into two categories optical (typically laser) methods or methods based on inertial impaction. 

Experimental method to measure the effectiveness of an explosive. The radial expansion on detonation of a metallic cylinder (usually copper) filled with a high explosive is observed. A streak camera or a laser method might be used. The detonation velocity is determined simultaneously, using for example time-of-arrival pins. The -> Equation of State (EOS) which is often the Jones-Wilkins-Lee (JWL) EOS of the detonation products is derived using Gurney theory. 

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