Femtosecond laser electronic excitation tagging for quantitative velocity imaging in air. Academic Article uri icon


  • Time-accurate velocity measurements in unseeded air are made by tagging nitrogen with a femtosecond-duration 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.

published proceedings

  • Appl Opt

author list (cited authors)

  • Michael, J. B., Edwards, M. R., Dogariu, A., & Miles, R. B.

citation count

  • 159

complete list of authors

  • Michael, James B||Edwards, Matthew R||Dogariu, Arthur||Miles, Richard B

publication date

  • September 2011