Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten.

MIR-Evaneszentwellenspektroskopie mit niedermodigen Wellenleitern

: Hahn, Peter

Fulltext ()

Freiburg, 2001, VI, 133 pp. : Ill.
Freiburg/Brsg., Univ., Diss., 2001
URN: urn:nbn:de:bsz:25-opus-2333
Dissertation, Electronic Publication
Fraunhofer IPM ()
Infrarotspektroskopie; Evaneszente Welle; Lichtwellenleiter; integrierte Optik; chemischer Sensor

This thesis deals with the physical basics and the application of evanescent field spectroscopy (EWS), which is based on the effect of attenuated total reflection. The EWS-method was employed for the spectroscopic detection of organic substances diluted in water in the mid infrared (MIR) wavelength range (2.5-25æm). In order to enhance the sensitivity of such a measurement, a solid phase extraction method was used to separate analyte molecules from the strongly absorbing water matrix and enrich them in a polymer coating placed in the evanescent field of the waveguide. In order to estimate and optimise the performance of a sensor system consisting of light source, sensing waveguide, wavelength selection, detector, and electronics a comprehensive physical model of such a system was developed. This model is based on the calculation of the flux of spectral power through the system. Two test systems for concentration measurements of organics in aqueous solutions were studied, detection limits in the low ppm concentration range were found for both systems. The application of the theoretical model exhibited the potential to enhance the sensitivity of both systems to the sub-ppm level. The development of low-modal planar MIR-waveguides carried out in this work aims at an increased sensitivity of EWS-systems. Planar waveguides were fabricated by depositing Germanium layers of 1.2 to 1.5æm thickness on Silicon substrates. The devices were characterised by m-line spectroscopy, showing high losses in the order of some 10dB/cm at a wavelength of 10.6æm. Although this values are too high for using the waveguides in sensor systems, an optimisation of the deposition process will most probably reduce the losses sufficiently.