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Femtosecond laser electronic excitation tagging for quantitative velocity imaging in air

机译:飞秒激光电子激发标记用于空气中的定量速度成像

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摘要

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 approx1 mJ, 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 660 nm 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.
机译:通过使用飞秒持续时间的激光脉冲标记氮气并使用延时快速门控的摄像头监控分子的位移,可以在非播种空气中进行时间精确的速度测量。厘米长的线穿过大约1 mJ的810nm激光的焦点区域写入,并通过非线性激发和离解氮产生。可以忽略不计的加热与这种相互作用有关。发射是由于氮原子的重新结合而产生的,在自然空气中持续了数十微秒。它属于560至660 nm的光谱区域,由与第一个正氮跃迁相关的多条光谱线组成。该概念的可行性通过在自由射流上书写的直线得到证明,产生瞬时和平均速度曲线。通过使用高强度飞秒脉冲进行流量标记,可以使用单个激光系统和摄像机精确确定速度分布。

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