Want to Read saving…. Aliasghar Sayfi marked it as to-read Apr 30, Page 2 — Index 1. While the general concept is unchanged, the new edition features a broad array of new material, e. Refresh and try again. Laser Spectroscopy : Basic Concept and Instrumentation, 3rd Edition Keeping abreast of the latest techniques and applications, this new edition of the standard reference and graduate text on laser spectroscopy has been completely revised and expanded.

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The red bands indicate "dirty" particles while cleaner ice particles are shown as turquoise in the outer parts of the rings. Raman, Raman spectroscopy measures the scattering of monochromatic light caused by a sample. The beam from an argon-ion laser is directed by a system of mirrors to a lens, which focuses monochromatic light onto the sample.

Most of the light bouncing off the sample scatters at the same wavelength as the incoming light, but some of the light does scatter at different wavelengths. This happens because the laser light interacts with phonons, or naturally occurring vibrations present in the molecules of most solid and liquid samples. These vibrations cause the photons of the laser beam to gain or lose energy. The shift in energy gives information about the phonon modes in the system and ultimately about the molecules present in the sample.

Advertisement Fluorescence refers to the visible radiation emitted by certain substances because of incident radiation at a shorter wavelength. In laser-induced fluorescence LIF , a chemist activates a sample usually with a nitrogen laser alone or a nitrogen laser in combination with a dye laser.

This excitation lasts for a few nanoseconds before the electrons return to their ground state. As they lose energy, the electrons emit light, or fluoresce, at a wavelength longer than the laser wavelength. Because the energy states are unique for each atom and molecule, the fluorescence emissions are discrete and can be used for identification.

For instance, some countries have adopted LIF to protect consumers from pesticide-tainted vegetables. The tool itself consists of a nitrogen laser, a sensor head and a spectrometer, all packaged in a small, portable system.

In some cases, the pesticides can be identified directly. In other cases, they must be identified based on how they interact with chlorophyll, the green pigment present in all leaves. The "P" in ICP stands for plasma, an ionized gas consisting of positive ions and free electrons. In nature, plasmas usually form only in stars , where the temperatures are high enough to ionize the gas.

But scientists can create plasmas in the lab using something known as a plasma torch. The torch consists of three concentric tubes of silica surrounded by a metal coil.

When an electric current passes through the coil, a magnetic field is created, which in turn induces electric currents in a gas, usually argon, allowed to pass through the silica tubes. This excites the argon gas and creates the plasma.

A nozzle at the end of the torch acts as an exit for the plasma. Now the instrument is ready to analyze a sample.





How Laser Analysis Works


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