Spectroscopic Light Sources

Fundamentally, the properties of laser light are concomitants of its coherence, which is in turn a consequence of the nature of stimulated emission. Most of these properties, especially brightness, monochromaticity, directionality, polarization, and coherence itself, are useful (for many applications, indis-pensible) in a spectroscopic light source. The spectroscopic potential of lasers was recognized even before they were invented. Actual applications remained very specialized until tunable lasers were devised. 

Fig. 12. A flash photolysis apparatus. 1, high-voltage power supply 2, 10 M12 resistor 3. high-voltage capacitor 4, coaxial cable 5, flash tube 6, vacuum system 7, reflector 8, pulsed spectroscopic light source 9, measuring cell 10, Hilger medium quartz spectrograph. (From Vallotton and Wild, Ref. ))...

II. Characteristic Features of Lasers as Spectroscopic Light Sources... 

There are five main qualities which make the laser an attractive spectroscopic light source ... 

In this reciew the attempt is made to exhibit some of the possibilities of laser applications in modem spectroscopy. The rapid development of new laser types and the improvement of the existing models lend lasers steadily increasing importance as spectroscopic light sources, and it seems that the laser revolution is only just beginning. These laser developments lead in different directions ... 

Contents Spectroscopy with Lasers Introduction. Characteristic Features of Lasers as Spectroscopic light Sources. Spectroscopic Applications of Lasers. High-Resolution Spectroscopy Based on Saturation Effects. Spectroscopy of Laser Media. Conclusion. Zusammen-fassung. (418 references). 

J2. Jones, W. J., and Walsh, A., Hollow-cathode discharges—the construction and characteristics of sealed-off tubes for use as spectroscopic light sources. Spectro-chim. Acta 16, 249-254 (1960). 

The ideal situation for a process analyzer is to have the detector/electrical components in an area physically isolated from the sample stream and any liquid components required for calibration or instrument operation (e.g., solvents for liquid chromatography or gel-permeation chromatography). In this arrangement, isolation of the electrical components ensures that a spark source or hot surface (such as a spectroscopic light source) will not cause a problem with flammable components (both sample stream components and solvents). Also, this isolation wiU limit instrument damage in case of a sample system leak or solvent leak. Although the ideal situation is often not realized in a practical application, one should make every effort to protect the delicate sections of the instrument. In one application of the authors, a fiber optic probe having a quartz window sealed on the end of the probe was installed in the reactor of a process that contained... 

Although these new techniques have proved to be very fruitful, the really stimulating impetus to the whole field of spectroscopy was given by the introduction of lasers. In many cases these new spectroscopic light sources may increase spectral resolution and sensitivity by several orders of magnitude. Combined with new spectroscopic techniques, lasers are able to surpass basic limitations of classical spectroscopy. Many experiments that could not be performed with incoherent light sources are now feasible or have already been successfully completed recently. This book deals with such new techniques of laser spectroscopy and explains the necessary instrumentation. 

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