Spectroscopy with Nonimaging Optics: Application to the Infrared Spectroscopy of Langmuir Monolayers

Abstract

We discuss the principles of nonimaging optics and demonstrate how nonimaging concentrators can be used to maximize the collection of low-intensity infrared light. Specifically, we show that infrared reflection-absorption spectra can be obtained from a Langmuir monolayer of heneicosanol with a reasonable number of scans. Preliminary results indicate that at 24 Å2/molecule and 6 dyne/cm a heneicosanol monolayer is in a crystalline phase with highly ordered, mostly all- trans molecules, and at 42 Å2/molecule and 0 dyne/cm the monolayer consists of islands of the crystalline phase in coexistence with disordered molecules in a liquid phase. The good signal-to-noise ratio of the spectra obtained demonstrates the important role that nonimaging optics has in spectroscopy, by maximizing light throughput, and we make several suggestions for its implementation in other spectroscopic applications.