Fourier transform infrared imaging of human hair with a high spatial resolution without the use of a synchrotron

The cross-section of a human hair has been imaged for the first time using the micro attenuated total reflection (ATR) Fourier transformed infrared (FT-IR) method in combination with a focal plane array (FPA) detector. A rigorous approach was applied to determine the spatial resolution, namely, measuring the distance over which the band absorbance changes from 95 to 5% of the maximum absorbance when passing through a sharp interface. The measured value for IR transmission was similar to16 mum, while the value obtained using ATR imaging was similar to5 mum. The enhanced spatial resolution achieved by this method allows the medulla of the hair (similar to8 mum in diameter) to be imaged clearly without the need for a synchrotron source. The spatial resolution of transmission and ATR imaging is compared, and advantages of ATR imaging are discussed.