Attenuated total reflection Fourier transform infrared imaging with variable angles of incidence: a three-dimensional profiling of heterogeneous materials.

Depth profiling in Fourier transform infrared (FT-IR) spectroscopic imaging has been demonstrated using a single reflection variable angle attenuated total reflection (ATR) accessory. Chemical information about samples can be obtained in three dimensions by acquiring ATR-FT-IR images at different angles of incidence through the ATR crystal. The image quality and field of view achieved at different angles of incidence has been discussed. A polymer film comprising two layers has been used as an example to demonstrate the principle of the measurement. The demonstrated approach is a promising tool to obtain depth profiles of heterogeneous materials. The extent of the measured depths is limited and ranges from approximately 0.3 to 4 microm, but the spatial resolution in the z-direction is not limited by diffraction. The development of this approach opens up the possibility to study the spatial heterogeneity of thin films including biological tissues, such as hair and skin, with high depth resolution.