Quantitative coating thickness determination

This reflective non-absorbing background serves as a reference for assessing the performance of the models. The hysperspectral imaging setup used in this study consisted of an IMSPECTOR V10E (Specim©) spectral camera, operating in the 400-1000 nm range. The visible range was selected due to the main absorption characteristics of the studied coating layers which is within the range of 400-1000nm.Optical Coherence Tomography (OCT) is a suitable technique for imaging the interfaces in a semi-transparent material and is therefore a logical choice for measuring coating thickness.

This technique is based on low-coherence interferometry to measure light reflections from refractive index interfaces. As shown in Fig. 5, a customized OCT system was built by using a superluminescent diode (FESL-1550-20-BTF, Frankfurt Laser Company) centered at 1550 nm with a full width at half maximum of 60 nm, resulting in a 20 µm spot size and an 11 µm theoretical axial resolution inside the coating layer (considering a refractive index of 1.5).

Depth-scanning for OCT was realized by the means of an optical delay line (ODL-650,MC, OZ Optics, Ltd). Lateral scanning of a sample with an x-y translation stage (T-LS28M, Zaber Inc., Canada) allowed for a 28 mm scanning range in two directions. Obtained data were bandpass filtered and an envelope detector was used to recover the depth dependent signal.