Laser-Induced Fluorescence in Gaseous I2 Excited with a Green Laser Pointer

Joel Tellinghuisen
Department of Chemistry, Vanderbilt University, Nashville, TN 37235
J. Chem. Educ., 2007, 84 (2), p 336
DOI: 10.1021/ed084p336
Publication Date (Web): February 1, 2007
History, Education, and Documentation

Abstract

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.

Keywords (Audience):

Graduate Education / Research

Keywords (Domain):

Demonstrations

Keywords (Feature):

Advanced Chemistry Classroom and Laboratory

Keywords (Pedagogy):

Misconceptions / Discrepant Events

Keywords (Subject):

Fluorescence Spectroscopy
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  • Received: August 03, 2009

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