Femtosecond laser electronic excitation tagging for quantitative velocity imaging in air

James B. Michael, Matthew R. Edwards, Arthur Dogariu, Richard B. Miles

Research output: Contribution to journalArticlepeer-review

184 Scopus citations


Time-accurate velocity measurements in unseeded air are made by tagging nitrogen with a femtosecondduration laser pulse and monitoring the displacement of the molecules with a time-delayed, fast-gated camera. Centimeter-long lines are written through the focal region of a ∼1mJ, 810nm laser and are produced by nonlinear excitation and dissociation of nitrogen. Negligible heating is associated with this interaction. The emission arises from recombining nitrogen atoms and lasts for tens of microseconds in natural air. It falls into the 560 to 660nm spectral region and consists of multiple spectral lines associated with first positive nitrogen transitions. The feasibility of this concept is demonstrated with lines written across a free jet, yielding instantaneous and averaged velocity profiles. The use of high-intensity femtosecond pulses for flow tagging allows the accurate determination of velocity profiles with a single laser system and camera.

Original languageEnglish (US)
Pages (from-to)5158-5162
Number of pages5
JournalApplied Optics
Issue number26
StatePublished - Sep 10 2011

All Science Journal Classification (ASJC) codes

  • Engineering (miscellaneous)
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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