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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 ∼16 μm, while the value obtained using ATR imaging was ∼5 μm. The enhanced spatial resolution achieved by this method allows the medulla of the hair (∼8 μm 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.