Spectroscopy is the study of the effect of electromagnetic radiation on matter. The result applying radiation to matter is recorded as a function of wavelength. In laser spectroscopy, a laser beam is trained on a sample and the interaction between the energy and matter is measured as a function of wavelength or frequency.
There are different methods of spectroscopy that rely on the qualities of matter to either absorb or emit light.
Absorption Spectroscopy distinguishes different atoms or molecules by measuring the absorption of energy versus the wavelength that is not absorbed. At the infrared range, molecules have relatively strong and narrow absorption lines versus wavelength. However, at the same wavelength, molecules can have similar or overlapping absorption lines that can prevent clear identification. Using a wider wavelength range may result in more distinction. With a tunable laser, absorption can be measured as a function of the wavelength of the laser and more criteria may be available for identification.
In Emission Spectroscopy, matter is excited so that it emits or scatters light.
One form of Emission Spectroscopy is Laser Induced Breakdown Spectroscopy (LIBS). In LIBS, a laser is focused on sample. The laser ablates a small amount of material which generates a plasma plume. The light emitted by the sample as it cools is measured to identify the material. Because only a very small amount of the material is consumed LIBS is considered essentially non-destructive.
Another form of Emission Spectroscopy is Laser-induced Fluorescence Spectroscopy (LIF). LIF involves the electronic excitation of an atom or molecule by a laser, causing it to reach a higher energy state, followed by a spontaneous emission of light. The molecule is excited by absorbing a photon, and the energy is released in the form of a photon when the electron returns to a lower energy state. Different molecules will emit photons with different energies or frequencies.
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