OH自由基共振荧光的门控光子计数测量

Gated Photon Counting Technique for the Measurement of the OH Radical Resonance Fluorescence

针对气体扩张激光诱导荧光测量低浓度OH自由基系统中短寿命低强度荧光的检测需求,提出了一种共振荧光的门控光子计数测量方法,通过光电倍增管的快速门控电路设计,实现纳秒级时序内荧光的选择性测量.使用一个13级高增益端窗光电倍增管进行荧光探测,通过改变光电倍增管打拿极上的加载电压来实现光电倍增管的快速门控.电路可获得稳定的调制电压,开关延迟时间为168ns,上升沿时间约20ns.对门控电路进行器件优化及匹配参量后,采用调制打拿极d1d3d5的方式,开关引起的光电倍增管噪声降至210ns以内,调制开关比优于10~5.将门控系统应用于气体扩张激光诱导荧光系统OH自由基的荧光探测,有效获得自由基荧光信号.对307.8~308.2nm波段内的OH自由基激发谱线进行了测量,实验结果表明,门控电路能有效抑制激光杂散光的影响,实现低浓度OH自由基共振荧光信号测量.

According to the needs of the detection of fluorescence with low concentration and short lifetime in the OH radical measurement based on fluorescence assay by gas expansion, a gated photon counting technique for resonance fluorescence detection was described, which was actualized by designing a nanosecond gating circuit applied to photomultiplier. Fluorescence was detected by a high gain 13-stage end-window photomultiplier, whose gating was actualized by changing the voltage of the photomultiplier dynodes. The circuit could obtain stable modulation voltage, with a 168 ns delay time and a 20 ns rising time. After optimizing the components and matching parameters of gating circuit, the radio frequency noise introduced by the circuit could be reduced in 210 ns and the on/off extinction could be up to 105 byswitching the voltage applied to the first, third and fifth dynode of the photomuhiplier. The gating system was applied to the fluorescence assay by gas expansion system for fluorescence detection and the OH radical fluorescence signal was obtained. The excitation spectrum of OH radical was measured in the wavelength range of 307.8 - 308.2 nm. Experiments show that the proposed gating technique can be used to suppress the influence of laser stray light, and detect the OH radical fluorescence signal in a particular time sequence.