A holographic alcohol sensor

A simple liquid-phase alcohol sensor based on a reflection hologram distributed throughout the volume of re crosslinked poly(hydroxyethyl methacrylate) film is described. The sensor is interrogated optically through the back of the film, by measuring the peak wavelength of the narrow-band reflection spectrum when the hologram is illuminated with white light. This procedure makes it possible to measure thickness changes in the film with great precision. The presence of alcohol in the sample medium causes the polymer film to swell in a concentration-dependent manner, whence the alcohol content can be determined by measurement of the wavelength of the reflected spectral peak. The sensor exhibits a wide dynamic range, which can easily be tuned for specific applications, and is unaffected by highly colored and turbid samples, since the light path does not pass through the sample. The sensor is relatively insensitive to pig in the range 3-6.5 and is highly stable, both in use and in storage, The performance of the sensor was demonstrated by measuring the alcohol contents of a wide range of alcoholic beverages such as wines and beers, with no sample pretreatment. Most alcohol concentrations were determined to be within approximately +/-0.3 vol % of their stated values.