Integrated optical chemical vapor microsensors

Abstract

We have recently demonstrated that an integrated optical waveguide chemical vapor microsensor may be fabricated on a glass support using a laser source capable of photopolymerizing a commercial dimethacrylate ester resin, to which a photocatalyst was added to the starting material. It was shown that this type of integrated sensor responded selectively to those vapors that could either be solubilized by the polymer structure or could produce an acid-base surface reaction. We have extended this microfabrication technique to another commercial oligomer material to which the photocatalyst is already incorporated into the starting material. Planar integrated optical waveguide structures were readily photopolymerized on glass substrates using a 100 W incoherent mercury arc source. These structures, when exposed to a series of organic vapors including water vapor, showed a selective response to only acetone and chloroform vapors. The apparent selectivity in these two cases arises from a partial solubilization of these condensed vapors into the photopolymerized waveguide structure, resulting in a slight swelling and hence a change in the optical path of the total internally reflected probe beam. Vapor concentration studies in a nitrogen-vapor dynamic flow system indicated detection levels of acetone and chloroform at 10 000 ppm at atmospheric pressure and room temperature.