Applications of Lasers

In many of the sophisticated experimental techniques applied to photophysical problems, the rapid development of the laser has enabled results to be obtained which were unheard of only a few years ago. These developments have been described adequately in previous and current volumes, but there are two applied uses of the laser which have not yet received significant attention, and to which readers attention is drawn by this short extra section this year. The first is concerned with the remote sensing of atmospheric pollutants. The methods available to achieve this object can be classified as passive, for example the heterodyne detection of thermal emission,209 or active, involving some radiation source. The means of attenuating the intensity of such a source are listed below. 

The methods may be compared with the widely used chemiluminescent method for NO in which the luminescence arising from reaction (81) is monitored.281 

The second recent interesting application of lasers is concerned with the use of the narrow spectral bandwidth of the laser as a means of selectively exciting single components in mixtures, particularly in isotopic mixtures, thus achieving selective reaction and ultimately isotope separation. In order to obtain high selectivity, in general a two-step excitation process is required, but one-photon radiation of several species with i.r. lasers has been shown to lead to enhancement of reaction rates. Thus C02-laser-induced vibrational excitation of 03 leads to enhancement of reaction rates with SO (85), NO (86), and SF4-02 mixtures.222 

The COa laser has been used to promote reactions in SFe-CaHe mixtures283 [(87)—(91)], the results being equivalent to heating the system, but this has been 

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Another application of laser-based profilometry is the inspection of rocket and missile components. The U.S. Air Force has funded work to develop a non-contact laser-based profilometer for the inside surface of solid rocket motors. Over time, these devices are subject to slumping and cracking, which could potentially render the rocket motor ineffective and hazardous. When fully implemented, this system will provide a meaningful screening method for evaluating the condition of aging rocket motors. 

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

The first half of this section discusses the use of the crossed beams method for the study of reactive scattering, while the second half describes the application of laser-based spectroscopic metliods, including laser-mduced fluorescence and several other laser-based optical detection teclmiques. Furtlier discussion of both non-optical and optical methods for the study of chemical reaction dynamics can be found in articles by Lee [8] and Dagdigian [9]. 

Laser desorption is commonly used for pyrolysis/mass spectrometry, in which small samples are heated very rapidly to high temperatures to vaporize them before they are ionized. In this application of lasers, very small samples are used, and the intention is not simply to vaporize intact molecules but also to cause characteristic degradation. 

J. P. Ready, Industrial Applications of Lasers, Academic Press, New York, 1978. 

APPLICATION OF LASER BASED MASS-SPECTROMETRIC METHODS FOR TRACE ANALYSIS OF SYNTHETIC AND NATURAL CRYSTALS... 

Initial results prove the high potential of LA-based hyphenated techniques for depth profiling of coatings and multilayer samples. These techniques can be used as complementary methods to other surface-analysis techniques. Probably the most reasonable application of laser ablation for depth profiling would be the range from a few tens of nanometers to a few tens of microns, a range which is difficult to analyze by other techniques, e. g. SIMS, SNMS,TXRE, GD-OES-MS, etc. The lateral and depth resolution of LA can both be improved by use of femtosecond lasers. 

Though as yet in its infancy, the application of laser Raman spectroscopy to the study of the nature of adsorbed species appears certain to provide unusually detailed information on the structure of oxide surfaces, the adsorptive properties of natural and synthetic zeolites, the nature of adsorbate-adsorbent interaction, and the mechanism of surface reactions. 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

Japanese researchers are ahead of their U.S. counterparts in the application of laser and electron beams and solid-phase epitaxy for the fabrication of silicon-on-insulator structures. 

Vol. 87. Analytical Applications of Lasers. Edited by Edward H. Piep-meier... 

Application of laser diagnostics to probe elementary reaction processes and the structure of flames. 

Temporal sequence of OH-LIF measurements captures a localized extinction event in a turbulent nonpremixed CH4/H2/N2 jet flame (Re 20,000) as a vortex perturbs the reaction zone. The time between frames is 125 ps. The velocity field from PIV measurements is superimposed on the second frame and has the mean vertical velocity of 9m/s subtracted. (From Hult, J. et al.. Paper No. 26-2, in 10th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 2000. With permission.)... 

To carry out a spectroscopy, that is the structural and dynamical determination, of elementary processes in real time at a molecular level necessitates the application of laser pulses with durations of tens, or at most hundreds, of femtoseconds to resolve in time the molecular motions. Sub-100 fs laser pulses were realised for the first time from a colliding-pulse mode-locked dye laser in the early 1980s at AT T Bell Laboratories by Shank and coworkers by 1987 these researchers had succeeded in producing record-breaking pulses as short as 6fs by optical pulse compression of the output of mode-locked dye laser. In the decade since 1987 there has only been a slight improvement in the minimum possible pulse width, but there have been truly major developments in the ease of generating and characterising ultrashort laser pulses. 

The increasing application of laser ablation or induced techniques for local and bulk analysis, whereby either the sampled vapor or the excited light becomes trans-... 

There are a few drawbacks to this method. Using 4 or 5 TIMS measurements to produce a U-series date profile across a bone is time consuming, although a single reliable U-series date is surely worth hundreds where the accuracy is not known. In future, the application of Laser-Ablation ICP-MS to measuring profiles will significantly reduce the analytical effort required to obtain a date. 

On-line SFE-GC-MS was used for the analysis of organic extractables from human hair [312]. Van Lieshout et al. [313] described GC-MS analysis of an SFE extract of an (ABS) impact-modified PC/PBT blend identifying Ionol CP, Dressinate, cyclic PBT trimer, Irganox 1076 and Irganox PS 800. TD-GC-MS was used in the development of flame retardants, and for the analysis of fire debris [314]. The application of laser desorption fast GC-MS analysis was employed in the analysis of DOP on a stainless-steel surface [221]. 

T. Arakawa, Applications of laser light scattering techniques to molecular biology, Cell Technol., 15(5), 679 (1996). 

The advancement of the application of lasers in combination with the molecular beam technique has made a great impact in the understanding of primary photodissociation processes. For state-specific detection of small fragments, laser-induced fluorescence, multiphoton ionization, and coherent laser scattering have provided extremely detailed information on the dynamics of photodissociation. Unfortunately, a large number of interesting... 

The technical application of thulium is limited. However, the element is becoming increasingly important in special applications of lasers. 

Secondary Ion Mass Spectrometry Basic Concepts, Instrumental Aspects, Applications and Trends. By A. Benninghoven, F. G. Ruenauer, and H.W.Werner Analytical Applications of Lasers. Edited by Edward H. Piepmeier Applied Geochemical Analysis. By C. O. Ingamells and F. F. Pitard Detectors for Liquid Chromatography. Edited by Edward S.Yeung Inductively Coupled Plasma Emission Spectroscopy Part 1 Methodology, Instrumentation, and Performance Part II Applications and Fundamentals. Edited by J. M. Boumans... 

Jia W.J., He A.D., Wang Z.L., Chin C.T., Application of laser-induced optical fiber fluorimetry to the analysis of ultralow level of uranium, J. Radioanal Nucl. Ch. 1987 108 33. 

Prochazka M., Mojzes P., Stepanek J., Vlckova B., Turpin P.Y., Probing applications of laser ablated Ag colloids in SERS spectroscopy Improvement of ablation procedure and SERS spectral testing, Anal. Chem. 1997 69 5103-5108. 

Besides the well-established chromatographic/mass spectrometric or spectroscopic methods there is always a need for complementary methods for the study of organic materials from art objects. The application of laser desorption/ionisation mass spectrometry (LDI-MS) methods to such materials has been reported only sporadically [12, 45 48] however, it is apparently increasing in importance. After GALDI-MS had been applied to triterpenoid resins, as described in Section 5.2, this relatively simple method was evaluated for a wider range of binders and other organic substances used for the production or conservation of artwork. Reference substances as well as original samples from works of art were analysed. 

Richard N. Zare is Marguerite Blake Wilbur Professor in Natural Science in the Department of Chemistry at Stanford University. He received his B.A. in 1961 and his Ph.D. in 1964 from Harvard University. His research areas are physical and analytical chemistry with specialized interests in application of lasers to chemical problems, molecular structure, molecular reaction dynamics, and chemical analysis. Zare has been a member of various NRC committees and served as co-chair of the Commission on Physical Sciences, Mathematics, and Applications and chair of the National Science Board. He is a member of the National Academy of Sciences, and he received the U.S. National Medal of Science in 1983. 

Poliakoff, M. Turner, J.J. "Chemical and Biochemical Applications of Lasers", Moore, C.B. Ed Academic Press ... 

The historical development and elementary operating principles of lasers are briefly summarized. An overview of the characteristics and capabilities of various lasers is provided. Selected applications of lasers to spectroscopic and dynamical problems in chemistry, as well as the role of lasers as effectors of chemical reactivity, are discussed. Studies from these laboratories concerning time-resolved resonance Raman spectroscopy of electronically excited states of metal polypyridine complexes are presented, exemplifying applications of modern laser techniques to problems in inorganic chemistry. 

Most chemical applications of lasers have fallen into three categories. Firstly, spectroscopic applications have utilized... 

In all of these applications, the emphasis to date has been on the use of lasers to study chemically and physically well characterized systems, that is, simple molecules in the gas phase, or in ordered phases such as molecular crystals, or in cryogenic matrices. There are exceptions to this statement, but the basic fact is that the great strides in chemical applications of lasers have been made by the chemical physics and analytical chemistry communities and largely ignored by inorganic, organic, and biological chemists. 

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