Lasers atomic spectroscopy

All the previous discussion in this chapter has been concerned with absorption or emission of a single photon. However, it is possible for an atom or molecule to absorb two or more photons simultaneously from a light beam to produce an excited state whose energy is the sum of the energies of the photons absorbed. This can happen even when there is no intemrediate stationary state of the system at the energy of one of the photons. The possibility was first demonstrated theoretically by Maria Goppert-Mayer in 1931 [29], but experimental observations had to await the development of the laser. Multiphoton spectroscopy is now a iisefiil technique [30, 31]. 

Sneddon, J., Thiem, T. and Lee, Y.-I. (1997) Lasers in Atomic Spectroscopy, John Wiley, New York. 

Adapted from Moenke-Blankenburg [217]. From L. Moenke-Blanken-burg, in Lasers in Analytical Atomic Spectroscopy (J. Sneddon et al., eds), VCH Publishers, New York, NY (1997), pp. 125-195. Reproduced by permission of Wiley-VCH. 

Baudelet M., Boueri M., Yu J., Mao S., Piscitelli V., Mao X., Russo R. 2007. Time-resolved ultraviolet laser-induced breakdown spectroscopy for organic material analysis. Spectrochimica Acta Part B Atomic Spectroscopy, 20,1329-1334. 

Evans, R. D. and Outridge, P. M. (1994). Applications of laser ablation inductively coupled plasma mass spectrometry to the determination of environmental contaminants in calcified biological structures. Journal of Analytical Atomic Spectroscopy 9 985-989. 

Raith, A., Hutton, R. C., Abell, I. D., and Crighton, J. (1995). Non-destructive sampling method of metals and alloys for laser ablation-inductively coupled plasma mass spectrometry. Journal of Analytical Atomic Spectroscopy 10 591-594. 

Watling, R. J., Lynch, B. F., and Herring, D. (1997). Use of laser ablation inductively coupled plasma mass spectrometry for fingerprinting scene of crime evidence. Journal of Analytical Atomic Spectroscopy 12 195-203. 

CONTENTS Preface, Joseph Sneddon. Analyte Excitation Mechanisms in the Inductively Coupled Plasma, Kuang-Pang Li and J.D. Winefordner. Laser-Induced Ionization Spectrometry, Robert B. Green and Michael D. Seltzer. Sample Introduction in Atomic Spectroscopy, Joseph Sneddon. Background Correction Techniques in Atomic Absorption Spectrometry, G. Delude. Flow Injection Techniques for Atomic Spectrometry, Julian F. Tyson. 

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

TCLP TDB TDF THC TBP TEM TLM TM-AFM TOC TRLFS TRU TSP TST TVS Toxicity characteristics leaching procedure Thermodynamic database Tyre-derived fuel Total hydrocarbon Tri-n-butyl phosphate Transmission electron microscopy Triple layer model Tapping mode atomic force microscopy Total organic carbon Time-resolved laser fluorescence spectroscopy Transuranic Total suspended particles Transition state theory Transportable vitrification system... 

In atomic spectroscopy, a substance is decomposed into atoms in a flame, furnace, or plasma. (A plasma is a gas that is hot enough to contain ions and free electrons.) Each element is measured by absorption or emission of ultraviolet or visible radiation by the gaseous atoms. To measure trace elements in a tooth, tiny portions of the tooth are vaporized (ablated) by a laser pulse1 and swept into a plasma. The plasma ionizes some of the atoms, which pass into a mass spectrometer that separates ions by their mass and measures their quantity. 

Other approaches have been taken for on-line analysis of individual aerosol particles as well. Laser spark spectroscopy (33) vaporizes individual particles in the breakdown plasma created by a pulsed laser. Atomic emission spectra can then be used to deduce the elemental composition of the particle that was vaporized. The timing of the laser pulse is critical because the particle must be caught in the focal volume of the pulsed laser, so a second laser is used to detect the particle and trigger the pulsed laser. To date the technique has been applied to large particles, that is, coal particles on the order of 60 to 70 xm in diameter in combustion studies. The use of inductively coupled plasma would eliminate the complex triggering and might allow on-line analysis of smaller particles spectroscopically. 

For many reasons atomic spectroscopy continues to be one of the most rapidly developing branches of physics. This is primarily due to the creation of very stable and monochromatic lasers, allowing one to selectively excite various atomic states, to create very highly excited (Rydberg) atoms, and due to the occurrence of new possibilities, given by non-atmospheric astrophysics, which allow one to register the electromagnetic radiation... 

R. Neumann, F. Trager and G. zu Putlitz. Laser-microwave spectroscopy. In H. J. Beyer and H. Kleinpoppen (eds). Progress in Atomic Spectroscopy, part D, Plenum, New York, 1987. 

The rest of the apparatus is the same as when operated at the Proton Synchrotron. First tested on cesium [ HUB 78 ], [ THI 81 ] the apparatus was used to uncover the resonance lines of francium for which no optical transition had ever been observed. The CERN on line mass separator, Isolde, makes available a source of more than 10 atoms/sec of chemically and isotopically pure 213 Fr isotope. Such an amount is more than needed for a laser atomic beam spectroscopy. The first step is obviously to locate the resonance line at low resolution, using a broad band laser excitation. In a second step, once the line is located, a high resolution study is undertaken, [ LIB 80] and [ BEN 84]. The observed signal is displayed (fig 3a) at low resolution and(3 b)at high resolution. 

Broadhead, M., Broadhead, R., and Hager, J.W. (1990) Laser sampling ICP-MS semi-quantitative determination of sixty-six elements in geological samples. Atomic Spectroscopy 11, 205-209. 

The rapid development of techniques for cooling and trapping atoms using laser light has created a new subfield of atomic physics. Research opportunities include the study of matter at ultra low temperature, ultra precise atomic spectroscopy and the study of light-matter interaction in a new quantum regime. 

T. W. Hansch, I. S. Shahin, and A. L. Schawlow, Optical Resolution of the Lamb Shift in Atomic Hydrogen by Laser Saturation Spectroscopy, Nature Physical Science 235, 63-65 (1972). 

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