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15.7: High-Resolution Laser Spectroscopy

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    One of the advantages of laser spectroscopy is that the linewidth of a laser beam is much smaller than the linewidth of a beam produced by a broadband source, such as an incandescent lamp. Although an incandescent lamp is polychromatic, the optics of the spectrometer (length of monochromator, grooves per millimeter on the diffraction grating, etc) can be used to obtain a resolution of about 0.03 cm-1. The use of a Michelson interferometer and Fourier transform processing is another means of obtaining high spectral resolution from a broadband source. Because a laser emits essentially monochromatic light, the output beam can have a linewidth that is inherently factors of ten smaller than the linewidth obtained from any broadband source. This very small linewidth has led to the development of high-resolution laser spectroscopy, which provides spectra with great detail, including the resolution of the interactions between electron spins and nuclear spins called hyperfine interaction.

    Figure \(\PageIndex{1}\) shows a comparison of a section of the absorption spectrum of ICl (g) obtained with an incandescent lamp light source to the same section of a spectrum obtained with a high-resolution laser spectrometer. The two peaks in figure \(\PageIndex{1a}\) correspond to absorptions from the ground electronic state to two different rotational states of the first excited electronic state. Figure \(\PageIndex{1b}\) shows the multiple absorption bands that can be resolved from the two broad peaks because of the smaller linewidth of the laser beam.

    ICl mod.png
    \(\tilde{\nu} / cm^{-1}\) Figure \(\PageIndex{1a}\): The absorption spectrum of ICl (g) measured with a spectrometer with a spectral resolution of around 0.03 cm-1.
    Figure \(\PageIndex{1b}\): The absorption spectrum of ICl (g) measured with a high- resolution laser spectrometer with a spectral resolution of around 0.00003 cm-1.




    15.7: High-Resolution Laser Spectroscopy is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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