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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 47, Iss. 26 — Sep. 10, 2008
  • pp: 4672–4683

Comparison of nanosecond and picosecond excitation for interference-free two-photon laser-induced fluorescence detection of atomic hydrogen in flames

Waruna D. Kulatilaka, Brian D. Patterson, Jonathan H. Frank, and Thomas B. Settersten  »View Author Affiliations


Applied Optics, Vol. 47, Issue 26, pp. 4672-4683 (2008)
http://dx.doi.org/10.1364/AO.47.004672


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Abstract

Two-photon laser-induced fluorescence (TP-LIF) line imaging of atomic hydrogen was investigated in a series of premixed CH 4 / O 2 / N 2 , H 2 / O 2 , and H 2 / O 2 / N 2 flames using excitation with either picosecond or nanosecond pulsed lasers operating at 205 nm . Radial TP-LIF profiles were measured for a range of pulse fluences to determine the maximum interference-free signal levels and the corresponding picosecond and nanosecond laser fluences in each of 12 flames. For an interference-free measurement, the shape of the TP-LIF profile is independent of laser fluence. For larger fluences, distortions in the profile are attributed to photodissociation of H 2 O , CH 3 , and/or other combustion intermediates, and stimulated emission. In comparison with the nanosecond laser, excitation with the picosecond laser can effectively reduce the photolytic interference and produces approximately an order of magnitude larger interference-free signal in CH 4 / O 2 / N 2 flames with equivalence ratios in the range of 0.5 Φ 1.4 , and in H 2 / O 2 flames with 0.3 Φ 1.2 . Although photolytic interference limits the nanosecond laser fluence in all flames, stimulated emission, occurring between the laser-excited level, H ( n = 3 ) , and H ( n = 2 ) , is the limiting factor for picosecond excitation in the flames with the highest H atom concentration. Nanosecond excitation is advantageous in the richest ( Φ = 1.64 ) CH 4 / O 2 / N 2 flame and in H 2 / O 2 / N 2 flames. The optimal excitation pulse width for interference-free H atom detection depends on the relative concentrations of hydrogen atoms and photolytic precursors, the flame temperature, and the laser path length within the flame.

© 2008 Optical Society of America

OCIS Codes
(280.1740) Remote sensing and sensors : Combustion diagnostics
(300.2530) Spectroscopy : Fluorescence, laser-induced
(350.3450) Other areas of optics : Laser-induced chemistry

ToC Category:
Spectroscopy

History
Original Manuscript: May 6, 2008
Manuscript Accepted: July 24, 2008
Published: September 4, 2008

Citation
Waruna D. Kulatilaka, Brian D. Patterson, Jonathan H. Frank, and Thomas B. Settersten, "Comparison of nanosecond and picosecond excitation for interference-free two-photon laser-induced fluorescence detection of atomic hydrogen in flames," Appl. Opt. 47, 4672-4683 (2008)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-47-26-4672

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