Laser-Induced Fluorescence (LIF) provides the temperature and flow velocity of a target species by direct measurement of its velocity distribution via Doppler shift. A LIF diagnostic has been developed at the Caltech water-ice dusty plasma experiment that uses an ultra-narrow tunable diode laser to pump the λvac = 696.735 nm argon neutral transition. A photomultiplier detects fluorescence emission at λvac = 772.633 nm. Signal to noise ratios in excess of 100 are achieved along with a high degree of reproducibility between measurements. A Labview program fully automates data collection throughout the three-dimensional plasma volume by controlling four stepper motors and recording measured data. The argon neutral temperature is measured to be slightly above room temperature. Challenges such as the lack of absolute calibration of diode lasers and wavelength drift due to slight changes in ambient room conditions are overcome to measure bulk neutral flow speeds on the order of 1-2 m/s with resolution on the order of 2/3 of a meter per second. High-speed video shows that introducing an argon flow to a cloud of ice grains causes the cloud of ice grains to move and change shape. Ice grain motion is analyzed and found to be in agreement with neutral LIF flow measurements. Surprisingly, when the flow ceases, the ice grain cloud reverts to its original location and shape.

中文翻译：

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尘埃等离子体实验中非常缓慢的中性流的激光诱导荧光测量

激光诱导荧光 (LIF) 通过多普勒频移直接测量目标物种的速度分布，提供目标物种的温度和流速。在加州理工学院水冰尘埃等离子体实验中开发了 LIF 诊断，该实验使用超窄可调谐二极管激光器泵浦 λvac = 696.735 nm 氩中性跃迁。光电倍增管检测 λvac = 772.633 nm 处的荧光发射。实现了超过 100 的信噪比以及测量之间的高度再现性。Labview 程序通过控制四个步进电机并记录测量数据，使整个三维血浆体积中的数据收集完全自动化。氩气中性温度经测量略高于室温。克服了诸如缺乏二极管激光器的绝对校准和由于室内环境条件的轻微变化导致的波长漂移等挑战，以测量 1-2 m/s 的体积中性流速，分辨率为 2/3一米每秒。高速视频显示，将氩气流引入冰粒云会导致冰粒云移动并改变形状。分析冰粒运动并发现其与中性 LIF 流量测量值一致。令人惊讶的是，当流动停止时，冰粒云恢复到原来的位置和形状。高速视频显示，将氩气流引入冰粒云会导致冰粒云移动并改变形状。分析冰粒运动并发现其与中性 LIF 流量测量值一致。令人惊讶的是，当流动停止时，冰粒云恢复到原来的位置和形状。高速视频显示，将氩气流引入冰粒云会导致冰粒云移动并改变形状。分析冰粒运动并发现其与中性 LIF 流量测量值一致。令人惊讶的是，当流动停止时，冰粒云恢复到原来的位置和形状。