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2007
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February
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In the Laboratory
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Advanced Chemistry Classroom and Laboratory
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Laser-Induced Fluorescence in Gaseous I2 Excited with a Green Laser Pointer
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Joel Tellinghuisen
Department of Chemistry, Vanderbilt University, Nashville, TN 37235
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February 2007
Vol. 84 No. 2
p. 336
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| Abstract |
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The use of a green laser pointer to excite fluorescence in gaseous I2 results in an unexpected behavior: on transiting the cell, the beam alternately appears brightly and vanishes completely. This behavior is attributed to temporal changes in the laser’s operating wavelength, likely due to temperature changes of the optical cavity as it warms up under power. As a result, the laser tunes itself into and out of resonance with the I2 absorption lines in the region of the laser gain profile. For this explanation to hold, it is also necessary that the laser operate with relatively high spectral purity, meaning a small number of narrow lasing modes. Spectra recorded for several different pointers display widely varying properties: some pointers operate on a single mode much of the time, while others emit in many weak lines in addition to one or two strong ones. Green laser pointers and an Ar-ion laser are used together to excite gaseous I2, illustrating in a comprehensive way the conditions necessary for laser-induced fluorescence in a gas. Spectra are observed with a hand spectroscope and photographed through the spectroscope with a digital camera. Complementary spectral phenomena are illustrated by exciting I2 with a Tesla discharge. Most of the information is best appreciated photographically, to which end a PowerPoint illustration is provided in the Supplemental Material.
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| Supplement |
Color versions of Figures 1, 4, 5, and 6 and four QuickTime movies illustrating the temporal behavior of the fluorescence and of the discharges obtained by bringing the low- and high-pressure cells into contact with an operating Tesla coil are available.
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Download |
Contents |
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JCE2007p0336W.zip
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Folder JCE2006p0336W [341 MB] including Sup_2005-0540.ppt (Microsoft PowerPoint) and four movie files (Quicktime)
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| More Information |
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Citation |
Tellinghuisen, Joel. J. Chem. Educ. 2007, 84, 336.
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Keywords |
Demonstrations; Fluorescence Spectroscopy; Graduate Education / Research; Laboratory Instruction; Lasers; Misconceptions / Discrepant Events; Physical Chemistry; Spectroscopy; Upper-Division Undergraduate; UV-Vis Spectroscopy
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History |
Created:
Last Updated: |
1/9/2007
2/23/2007
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 Caution! | | Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations. |
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