Waveguide spectroscopy

Alexander V. Khomchenko, Waveguide Spectroscopy of Thin Films, Volume 33, 2005. 

Combination of Surface Plasmon Resonance (SPR) and Optical Waveguide Spectroscopy (OWS) was used for the simultaneous determination of refractive index and film thickness of the hydrogel layers in the Kretschmann configuration [24], The resulting angle scans from the SPR instrument were fit to Fresnel calculations and different layers were represented using a simple box model. A detailed description of this process has been published previously [18]. 

In contrast to SPFS, SPR, and SPDS are tools that can study biomolecular interactions without external labels. They share the same category of label-free biosensors with the reflectometry interference spectroscopy (RIfS) [46], waveguide spectroscopy [47], quartz crystal microbalance (QCM) [48], micro-cantilever sensors [49], etc. Although the label-free sensors cannot compete with SPFS in terms of sensitivity [11], they are however advantageous in avoiding any additional cost/time in labeling the molecules. In particular, the label-free detection concept eliminates undue detrimental effects originating from the labels that may interfere with the fundamental interaction. In this sense, it is worthwhile to develop and improve such sensors as instruments complementary to those ultra-sensitive sensors that require labels. 

FIG. 4.7 Waveguide spectroscopy experimental arrangement in the ATg-Kretachmann s p. The probe is a 632.8 nm He-Ne laser beam, and the reflectivity of the sample is recorded as a function of the incidence angle. The irradiation (pump) beam direction of propagation is perpendicular to the plane of the sample. 

FIG. 6.23 Refractive indices for poty(L- utamate) 36 (n = 6) LBK films in the initial state before any irradiation, in the ds-photostationary state after irradiation at 365 nm, and in the trans-photostationary state after irradiation at 440 nm, determined by waveguide spectroscopy (data from reference 90). 

Structure upon the first irradiation with UV light enhances the effect of the photoisomerization on the refractive index/ (see Figure 6.22). Employing waveguide spectroscopy in thicker LBK films, the refractive indices can be determined. The values for LBK films of poly(L-glutamate) 38 are shown in Figure 6.23. 

The existence of an evanescent wave was discussed above (cf. Section III), together with PSPs. The optical properties of thicker LBK films can be characterized by the optical waveguide spectroscopy (WGS), and their layered structure can be probed by means of X-ray reflectometry. 

M. Mitsuishi, S. Ito, M. Yamamoto, H. Endo, S. Hachiya, T. Fischer, W. Knoll, Optical characterization of a ferroelectric liquid crystalline polymer studied by time-resolved optical waveguide spectroscopy. Macromolecules 31, 1565-1574 (1998)... 

Chu, L.Q., Tan, W.J., Mao, H.Q. and Knoll, W. 2006. Characterization of UV-induced graft polymerization of polyfacryhc acid) using optical waveguide spectroscopy. 

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