Use of analyte-modulated modal power distribution in multimode optical fibers for simultaneous single-wavelength evanescent-wave refractometry and spectrometry.
Use of analyte-modulated modal power distribution in multimode optical fibers for simultaneous single-wavelength evanescent-wave refractometry and spectrometry.
复制标题
使用多模光纤中的分析物调制模式功率分布进行同步单波长倏逝波折射测量和光谱测量。
DOI：
10.1021/ac990851t
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发表时间：
1999
影响因子：
7.4
通讯作者：
Hieftje,GM
中科院分区：
文献类型：
--
作者：
Potyrailo,RA;Ruddy,VP;Hieftje,GM
介绍了一种同时测定样品介质吸光度和折射率的新方法。该方法基于对多模波导中分析物调制模式功率分布(MPD)的测量。反过来，MPD通过远场空间图案和光的强度来量化，即从多模光纤出射的夫琅和费衍射图案(记录在CCD相机上)。在操作上，沿着光纤发送的光通过光纤边界处的消逝波与周围的含分析物的介质相互作用。传输光束中的光通量和光纤内的内部反射角都受到与分析物连接的光吸收和含分析物介质的折射率的影响。反过来，当光束离开光纤时，这些角度会反映在光束的角度发散中。因此，该光束的夫琅和费衍射图产生了两个参数，这两个参数可以一起用来推导折射率和吸光度。这种基于MPD的检测与传统的逝去波检测策略相比具有重要的优势，传统的消逝波检测策略仅依赖于记录总的传输光功率或其损失分数。首先，可以在单一探头波长下同时测定样品的折射率和吸光度。其次，折射率测量和吸收测量的灵敏度可以通过调整光纤端面和CCD探测器之间的距离或通过监测光纤输出的选定模组来简单地控制。作为这些能力的演示，研究了几种弱吸收溶液，它们的折射率在1.3330到1.4553之间，吸收系数在0−16 cm-1范围内。新的检测策略可能在样品颜色变化的应用中以及当需要补偿样品折射率的变化时很重要。
A new method is described for the simultaneous determination of absorbance and refractive index of a sample medium. The method is based on measurement of the analyte-modulated modal power distribution (MPD) in a multimode waveguide. In turn, the MPD is quantified by the far-field spatial pattern and intensity of light, i.e., the Fraunhofer diffraction pattern (registered on a CCD camera), that emerges from a multimode optical fiber. Operationally, light that is sent down the fiber interacts with the surrounding analyte-containing medium by means of the evanescent wave at the fiber boundary. The light flux in the propagating beam and the internal reflection angles within the fiber are both affected by optical absorption connected with the analyte and by the refractive index of the analyte-containing medium. In turn, these angles are reflected in the angular divergence of the beam as it leaves the fiber. As a result, the Fraunhofer diffraction pattern of that beam yields two parameters that can, together, be used to deduce refractive index and absorbance. This MPD based detection offers important advantages over traditional evanescent-wave detection strategies which rely on recording only the total transmitted optical power or its lost fraction. First, simultaneous determination of sample refractive index and absorbance is possible at a single probe wavelength. Second, the sensitivity of refractometric and absorption measurements can be controlled simply, either by adjusting the distance between the end face of the fiber and the CCD detector or by monitoring selected modal groups at the fiber output. As a demonstration of these capabilities, several weakly absorbing solutions were examined, with refractive indices in the range from 1.3330 to 1.4553 and with absorption coefficients in the range 0−16 cm-1. The new detection strategy is likely to be important in applications in which sample coloration varies and when it is necessary to compensate for variations in the refractive index of a sample.