Optimization of Microstructured Silicon Attenuated Total Reflectance Fourier Transform Infrared Elements

Microstructured silicon attenuated total reflection (ATR) Fourier transform infrared (FTIR) elements, commonly known as microstructured silicon reflection elements (μSREs), are gaining popularity as a low-cost, disposable alternative to ATR crystals in fields such as medical diagnostics. They comprise a silicon chip, with light incident on microprisms on the underside guided into the chip and totally internally reflecting at the sample interface. However, such devices are prone to issues, including poor limit of detection compared to traditional ATR crystals, and fringes within their spectra, whose origin has not been conclusively identified in the literature. This work, verified by experimental data, mathematically reveals the origin of these fringes to be an acquired phase difference between beams incident on the same μSRE prism face upon input, but exiting the μSRE through separate prism faces, resulting in interference. This improved understanding of the behavior of light within the μSRE will enable researchers to select appropriate μSRE designs for their application, maximizing the potential of this technology.