Ultra-sensitive probe of spectral line structure and detection of isotopic oxygen
Ultra-sensitive probe of spectral line structure and detection of isotopic oxygen
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DOI：
10.1007/s00340-017-6882-9
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发表时间：
2017
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影响因子：
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通讯作者：
Richard M. Garner;A. Dharamsi;M. A. Khan
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文献类型：
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作者：
Richard M. Garner;A. Dharamsi;M. A. Khan
本文讨论了一种基于信号结构的高次谐波（bbb2f）波长调制光谱（WMS）定量特性研究和获得的新方法。结果表明，高谐波WMS信号的光谱结构，通过零交叉点和转折点的数量来量化，可以增加对环境条件或温度、压力或光学深度变化引起的线展宽效应的敏感性。WMS信号的结构以信号幅度和拐点和过零点的频谱位置的组合为特征，提供了一种独特的尺度来量化线形参数，从而有助于从多谐波WMS信号中获得的测量结果的优化。我们通过在近红外区域检测到同位素大气氧（16O18O）较弱的旋转振动跃迁来证明这一点，在近红外区域，高谐波WMS信号比其信噪比考虑更敏感。所提出的基于光谱结构的方法提供了研究和量化信号的能力，不仅在线中心，而且在吸收剖面的翼区。该公式在可调谐二极管激光光谱和超精密激光传感器中特别有用，其中吸收信号剖面携带感兴趣的数量信息，例如浓度，速度或气体碰撞动力学等。
We discuss a new method of investigating and obtaining quantitative behavior of higher harmonic (> 2f) wavelength modulation spectroscopy (WMS) based on the signal structure. It is shown that the spectral structure of higher harmonic WMS signals, quantified by the number of zero crossings and turnings points, can have increased sensitivity to ambient conditions or line-broadening effects from changes in temperature, pressure, or optical depth. The structure of WMS signals, characterized by combinations of signal magnitude and spectral locations of turning points and zero crossings, provides a unique scale that quantifies lineshape parameters and, thus, useful in optimization of measurements obtained from multi-harmonic WMS signals. We demonstrate this by detecting weaker rotational–vibrational transitions of isotopic atmospheric oxygen (16O18O) in the near-infrared region where higher harmonic WMS signals are more sensitive contrary to their signal-to-noise ratio considerations. The proposed approach based on spectral structure provides the ability to investigate and quantify signals not only at linecenter but also in the wing region of the absorption profile. This formulation is particularly useful in tunable diode laser spectroscopy and ultra-precision laser-based sensors where absorption signal profile carries information of quantities of interest, e.g., concentration, velocity, or gas collision dynamics, etc.