Hammack Stephen, Carter Campbell, Wuensche Clemens, Lee Tonghun
Appl Opt. 2014 Aug 10;53(23):5246-51. doi: 10.1364/AO.53.005246.
This study demonstrates high-repetition-rate planar laser-induced fluorescence (PLIF) imaging of hydroxyl radicals (OH) in flames at a continuous framing rate of 50 kHz. A frequency-doubled dye laser is pumped by the second harmonic of an Nd:YAG laser to generate laser radiation near 283 nm with a pulse width of 8 ns and rate of 50 kHz. Fluorescence is recorded by a two-stage image intensifier and complementary metal-oxide-semiconductor camera. The average power of the 283 nm beam reaches 7 W, yielding a pulse energy of 140 μJ. Both a Hencken burner and a DC transient-arc plasmatron are used to produce premixed CH/air flames to evaluate the OH PLIF system. The average signal-to-noise ratio for the Hencken burner flame is greater than 20 near the flame front and greater than 10 further downstream in a region of the flame near equilibrium. Image sequences of the DC plasmatron discharge clearly illustrate development and evolution of flow features with signal levels comparable to those in the Hencken burner. The results are a demonstration of the ability to make high-fidelity OH PLIF measurements at 50 kHz using a Nd:YAG-pumped, frequency-doubled dye laser.
本研究展示了在50kHz的连续成帧速率下对火焰中羟基自由基（OH）进行高重复率平面激光诱导荧光（PLIF）成像。一台倍频染料激光器由Nd:YAG激光器的二次谐波泵浦，以产生波长接近283nm、脉宽为8ns且速率为50kHz的激光辐射。荧光由两级图像增强器和互补金属氧化物半导体相机记录。283nm光束的平均功率达到7W，脉冲能量为140μJ。使用亨肯燃烧器和直流瞬态电弧等离子体发生器来产生预混CH/空气火焰，以评估OH PLIF系统。在火焰前沿附近，亨肯燃烧器火焰的平均信噪比大于20，在火焰接近平衡的区域中，下游更远位置的平均信噪比大于10。直流等离子体发生器放电的图像序列清楚地展示了流动特征的发展和演变，其信号水平与亨肯燃烧器中的相当。结果表明，使用Nd:YAG泵浦的倍频染料激光器能够在50kHz下进行高保真的OH PLIF测量。
