Confocal Raman microscopy: how to correct depth profiles considering diffraction and refraction effects

A new approach to obtain corrected depth profiles by confocal Raman microscopy, which considers diffraction and refraction effects is presented. The problem of diffraction effects encountered intrinsically in the confocal. configuration can be described using a linear Fredholm integral equation of the first kind, which correlates apparent and true Raman intensities with the depth resolution curve of the instrument. Refractive index differences between air and the polymer sample, which cause further errors in the obtained depth profile due to strong aberration effects have been considered. This has been carried out using an empirical variation of the depth resolution function, which is able to simulate the broadening of the depth of focus with depth and also the discrepancy between nominal and measured depth scales. It is shown that considerable differences between apparent and corrected depth profiles exist at the surface and that these depend on the gradient of the profile and the depth resolution of the Raman microscope. Copyright (C) 2007 John Wiley & Sons, Ltd