Gillis K A, Havey D K, Hodges J T
Process Measurements Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Rev Sci Instrum. 2010 Jun;81(6):064902. doi: 10.1063/1.3436660.
We model and measure the absolute response of an intensity-modulated photoacoustic spectrometer comprising a 10 cm long resonator and having a Q-factor of approximately 30. We present a detailed theoretical analysis of the system and predict its response as a function of gas properties, resonance frequency, and sample energy transfer relaxation rates. We use a low-power continuous wave laser to probe O(2) A-band absorption transitions using atmospheric, humidified air as the sample gas to calibrate the system. This approach provides a convenient and well-characterized method for calibrating the absolute response of the system provided that water-vapor-mediated relaxation effects are properly taken into account. We show that for photoacoustic spectroscopy (PAS) of the O(2) A-band, the maximum conversion efficiency of absorbed photon energy to acoustic energy is approximately 40% and is limited by finite collision-induced relaxation rates between the two lowest-lying excited electronic states of O(2). PAS also shows great potential for high-resolution line shape measurements: calculated and experimental values for the PAS system response differ by about 1%.
我们对一台强度调制光声光谱仪的绝对响应进行建模和测量，该光谱仪包含一个10厘米长的谐振器，品质因数约为30。我们对该系统进行了详细的理论分析，并预测了其响应与气体特性、共振频率和样品能量转移弛豫率的函数关系。我们使用低功率连续波激光探测O(2) A带吸收跃迁，以大气中的加湿空气作为样品气体来校准系统。只要适当考虑水汽介导的弛豫效应，这种方法就能为校准系统的绝对响应提供一种方便且特征明确的方法。我们表明，对于O(2) A带的光声光谱（PAS），吸收的光子能量到声能的最大转换效率约为40%，并受到O(2)两个最低激发电子态之间有限的碰撞诱导弛豫率的限制。PAS在高分辨率线形测量方面也显示出巨大潜力：PAS系统响应的计算值和实验值相差约1%。
