Waveguide method

In the waveguide method, the sample is contained by the waveguide in the form of a block closely fitting the waveguide s bore. 

Optical waveguide methods (188,196-198) are based on the phase shift associated with multiple interfacial reflections when either the s- orp-wave undergoes a total phase shift equal to an integral multiple of 2jt upon one complete traversal of a planar, dielectric waveguide sandwiched between media of lower refractive index, a standing wave is excited in the waveguiding film. Because of their dependence on reflection, the phase shifts are sensitive to interfacial heterogeneity—and the thickness, refractive index, and density of an adsorbed biomolecular layer can be readily determined. 

A new one-dimensional mierowave imaging approaeh based on suecessive reeonstruetion of dielectrie interfaees is described. The reconstruction is obtained using the complex reflection coefficient data collected over some standard waveguide band. The problem is considered in terms of the optical path length to ensure better convergence of the iterative procedure. Then, the reverse coordinate transformation to the final profile is applied. The method is valid for highly contrasted discontinuous profiles and shows low sensitivity to the practical measurement error. Some numerical examples are presented. 

Lithium Niobate. Lithium niobate [12031 -64-9], LiNbO, is normally formed by reaction of lithium hydroxide and niobium oxide. The salt has important uses in switches for optical fiber communication systems and is the material of choice in many electrooptic appHcations including waveguide modulators and sound acoustic wave devices. Crystals of lithium niobate ate usually grown by the Czochralski method foUowed by infiltration of wafers by metal vapor to adjust the index of refraction. 

The reduction of dimensions also reduces volumes which are accessible to the detector. Thus, detection principles related to geometric dimensions of the detector cell ai e not ideally suited for coupling to microsystems, whereas surface sensitive principles, such as electrochemical methods or optical methods utilizing the evanescent field of a waveguide, or methods which can be focussed on a small amount of liquid, such as electrochemiluminescence (ECE), ai e better suited. This is why electrochemiluminescence detectors ai e combined to microsystems. Moreover ECE has found wide applications in biochemistry because of its high sensitivity, relatively simplicity and feasibility under mild conditions. 

We recognize that there are applications in two- and three-dimensional waveguides (12,13) which do not have the same criteria of phase-matching as in simple crystals or that one may just as well be interested in screening these materials for the related electrooptic performance by the simple SHG powder method. (It has been shown for several organic materials that although the electro-optic and SHG x tensors are in principle unequal, due to dispersion and due to the possible contribution of atomic and molecular distortions... 

A novel technique of producing waveguiding structures by growth of crystals in glass capillaries is presented. This method of crystal growth is simple and is particularly suited to organic materials. 

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