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Let us try as much as we can, we shall still unavoidably fail in many things 'The Imitation of Christ', Thomas a Kempis Since the invention of the laser in 1960, a steadily increasing number of applications has been found for this remarkable device. At first it appeared strangely difficult to fmd any obvious applications, and for several years the laser was often referred to as 'a solution in search of a problem'. The unusual properties of laser light were all too obvi­ ous, and yet it was not clear how they could be put to practical use. More and more ap­ plications were discovered as the years passed, however, and this attitude slowly changed until by the end of the 1970's there was scarcely an area of science and tech­ nology in which lasers had not been found application for one purpose or another. To­ day, lasers are utilised for such diverse purposes as aiming mjssiles and for eye surgery; for monitoring pollution and for checking out goods at supermarkets; for welding and for light-show entertainment. Even within the field of specifically chemical applica­ tions, the range extends from the detection of atoms at one end of the scale to the syn­ thesis of vitamin D at the other. In this book, we shall be looking at the impact which the laser has made in the field of chemistry.

Inhaltsverzeichnis

Frontmatter

1. Principles of Laser Operation

Abstract
The term laser, an acronym for light amplification by the stimulated emission of radiation, first appeared in 1960 and is generally held to have been coined by Gordon Gould, one of the early pioneers of laser development. Since the device was based on the same principles as the maser, a microwave source which had been developed in the 1950’s, the term ‘optical maser’ was also in usage for a time, but was rapidly replaced by the simpler term. In order to appreciate the concepts of laser action, we need to develop an understanding of the important term ‘stimulated emission’. First, however, it will be helpful to recap on the basic quantum mechanical principles associated with the absorption and emission of light. Although these principles apply equally to individual ions, atoms or molecules, it will save unnecessary repetition in the following discussion if we simply refer to molecules.
David L. Andrews

2. Laser Sources

Abstract
Since the construction of the first laser based on ruby, widely ranging materials have been adopted as laser media, and the range is still continually being extended to provide output at new wavelengths: according to Charles H. Townes, one of the pioneers of laser development, ‘almost anything works if you hit it hard enough’. As can be seen from a glance at Appendix 1, output from commercial lasers now covers most of the electromagnetic spectrum through from the microwave region to the ultraviolet, and much effort is being concentrated on extending this range to still shorter wavelengths. Amongst a host of tantalising possibilities is the prospect of obtaining holograms of molecules by use of an X-ray laser, for example.
David L. Andrews

3. Laser Instrumentation in Chemistry

Abstract
In the first two Chapters of this book, we have considered the chemical and physical principles underlying the operation of various types of laser, and the characteristic properties of the light which they emit. In the remainder of the book, we shall be concerned with chemical applications of lasers, paying particular attention to the ways in which each application has been developed to take the fullest advantage of the unique properties of laser light.
David L. Andrews

4. Chemical Spectroscopy with Lasers

Abstract
Spectroscopy is the study of the wavelength- or frequency-dependence of any optical process in which a substance gains or loses energy through interaction with radiation. In the last Chapter, we considered several strictly non-spectroscopic chemical techniques, mostly based on interactions with laser light at a fixed wavelength. The advantage of studying the wavelength-dependence is the much more detailed information which is made available. Since the exact spectral response is uniquely determined by the chemical composition of a sample, there are two distinct areas of application. Firstly, spectroscopy can be employed with pure substances for the purpose of obtaining more information on their molecular structure and other physicochemical properties; such are the research applications. Secondly, the characteristic nature of spectroscopic response can be utilised for the detection of particular chemical species in samples containing several different chemical components; these are the analytical applications. In both areas, lasers have made a very sizeable impact in recent years.
David L. Andrews

5. Laser-induced Chemistry

Abstract
In preceding Chapters, we have looked at a wide range of applications in which the laser is used as a probe for systems of chemical interest. Although the application of laser spectroscopic techniques in particular may result in short-lived changes in molecular energy level populations, the laser does not generally induce any chemical change in the sample; in that sense it is used as a static, rather than a dynamic tool. Quite distinct from this is the field of applications in which laser excitation is used specifically to promote chemical reaction. Although this is a less well-developed area, it is one which is growing at a very rapid rate, and includes perhaps some of the most exciting research topics in the whole field of lasers in chemistry, as we shall see. There are, for example, indications that laser-induced chemical synthesis may ultimately prove the best and most economically sound method of producing some of the more expensive pharmaceutical compounds. To introduce the subject, we begin with a general overview of the major principles appertaining to laser-induced chemistry.
David L. Andrews

6. Appendix 1: Listing of Output Wavelengths from Commercial Lasers

Abstract
The table below lists in order of increasing wavelength λ the emission lines of the most commonly available discrete-wavelength lasers over the range 100 nm–10 μm. Although continuously tunable lasers are not included, the molecular lasers which can be tuned to a large number of closely spaced but discrete wavelengths are listed at the end of the table. Harmonics are indicated by × 2, × 3 etc. Other parameters such as intensity and linewidth vary enormously from model to model, and no meaningful representative figure can be given. However the annually updated ‘Laser Focus Buyers’ Guide’ and ‘Lasers and Applications Designers’ Handbook’ both have comprehensive data on all commercially available lasers, together with manufacturers’ addresses.
David L. Andrews

7. Appendix 2: Directory of Acronyms and Abbreviations

Abstract
Bearing in mind the origin of the word ‘laser’ itself, it is perhaps inevitable that the field of laser applications is associated with a plethora of acronyms and abbreviations. The use of these has, as a matter of deliberate policy, been largely avoided in this book. Nonetheless, abbreviations are common in the current laser literature, and the following list has been selected to assist the reader.
David L. Andrews

8. Appendix 3: Selected Bibliography

Without Abstract
David L. Andrews

Backmatter

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