Mid-wave infrared liquid crystal shutter for breathalyzer applications

Abstract There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic C H stretch absorption bands in CH 3 and CH 2 functional groups in ethanol (CH 3 CH 2 OH) appear at a wavelength of λ  = 3.42 μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ  = 3.42 μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ  = 3.42 μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of C H bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of C H bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.