Slab Optical Waveguide Spectroscopy

@ Novel spectroscopic method named slab optical waveguide (SOWG) spectroscopy is reviewed. In recent years, slab optical waveguide (SOWG) techniques have been applied to optical sensing of surface chemical species and chemical reactions. SOWG spectroscopy is one of the SOWG technique in which white light is used as light source and an absorption spectrum of the sample is obtained in wide wavelength region, ultraviolet to near-infrared. Although, the SOWG acts as an internal reflection element (IRE) used in the attenuated total reflection (ATR) spectroscopy, the SOWG has much thinner core layer than IRE for ATR method an realizes a much larger number of total reflections in the core and higher sensitivity than conventional ATR spectroscopy. It is the most remarkable feature of the SOWG technique. First, structure, optical properties and fabrication methods of SOWGs are shown When light propagates in core layer of the SOWG, evanescent wave arises on the SOWG surface. Properties of the evanescent wavi and propagation mode of the SOWG are outlined. Related techniques using SOWG such as waveguide sensors are also reviewed. Four types of the SOWG chemical sensor are explained. One has sensing layer, which contains a chromophore. The second use: fluorescence and the SOWG act as transfer layer for exciting light. The third senses change of refractive index near the core layer The fourth type utilizes an electrochemical reaction. At the latter half of this review instrumentation of SOWG spectroscopy and results of our experiments are summarized. Sensitive spectroscopic measurements performed for LB films and adsorbed layer o proteins in visible to ultraviolet light region. Then, examples of combined use of electro-chemical method and photothermal method with SOWG technique are shown. In these methods we can do sensitive in-situ measurements of adsorbed molecules on liquid/solid interfaces.