摘要
光声光谱法是基于红外吸收光谱原理的一种高灵敏度的微量气体探测技术。它使用声共振腔来实现微弱声信号的共振放大。通过调节激光的调制频率，当它等于腔的某个共振频率时，在腔内形成声驻波，而腔本身的作用相当于一声放大器。共振腔的放大作用取决于当前被激活的共振模式、腔的品质因素、声传感器的状态以及电磁辐射与腔共振模式的耦合作用。值得关注的是，红外激光相对于声共振腔的入射方位不同则激励产生的光声信号幅值也不同。采用理论推导与数值计算相结合的方法，以圆柱形光声池为例，研究了径向共振模式下耦合系数受激光入射方位的影响。研究表明，激光入射角在0-π／2范围变化时耦合系数存在2个零点和2个极大值：入射角为。或tan^-1（0．8592×2R／L）时，耦合系数为零而径向共振失效；入射角为tan^-1（0．5568×2R／L）或tan^-1（2R／L）时，耦合系数极大而径向共振最强。此处R为池径而L为池长。结果可用于指导光声池结构优化设计与安装调试，增强光声法检测微量气体的信号幅值，提高检测灵敏度。
Photoacoustic detection of trace concentrations of gases is one of the most sensitive techniques of infrared absorption spectroscopy. High-sensitivity photoacoustic detectors apply an acoustic resonator for the amplification of the weak photoacoustic signal. If the modulation frequency coincides with one of the resonance frequencies of the chamber, a standing acoustic wave is excited and the system works as an acoustic amplifier. The amplification of the resonator relies on the acting mode, quality factor, nature of microphone, and the coupling between electromagnetic radiation and the stand wave resonance mode. With different incidence orientation of the modulated IR laser relative to acoustic chamber, the sound pressure magnitude of resonance mode varies. The influence of different laser incidence orientation on the coupling coefficients of radial resonance mode of cylindrical photoacoustic cells was investigated by both theoretical deduction and numerical computation method. It is concluded that the coupling coefficients have two zeros and two maximums when the laser incidence angle varies from 0 to π/2. When the incidence angle is 0 or tan 1（0. 859 2 × 2R/L）, the coupling coefficients are zeros and the radial resonance is invalid. When the incidence angle is tan-1 （0. 556 8 × 2R/L） or tan-1 （2R/L）, the coupling coefficients are the maximums and the radial resonance is the strongest. Here R is the radius and L the length of the cell. The results therein before give some theoretical guidelines for photoacoustic cell designing, optimizing, installing and adjusting, and for improvement of detection sensitivity in trace gas detectors through maximal excitement of radial modes in cylindrical acoustic cells.
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2010年第4期879-882,共4页
Spectroscopy and Spectral Analysis
基金
国家高技术研究发展计划项目(2006AA10Z214)
四川省教育厅项目(08zd1102)资助
关键词
光声池
声共振
耦合系数
Photoacoustic cells
Acoustic resonance
Coupling coefficients
