Terahertz layer thickness measurements is one of the most promising fields of applications for terahertz technology. Measuring subwavelength layers in multilayer systems is most commonly achieved by applying retrieval algorithms. These algorithms are computational demanding, which makes it hard for the evaluation to keep up with the increasing speed of modern terahertz systems. ECOPS-based systems now achieve measurement rates above 1 kHz. By applying a highly efficient algorithm based on desktop-grade CPU, we achieve multilayer imaging at 1.6 kHz measurement rate. A three-layer system on a metal disk of 300 mm diameter is measured in 2.5 minutes with 240000 pixels.
Layer-thickness measurement is one of the most promising and attractive fields of application for terahertz measurement systems, as they really provide benefits in comparison to competing techniques. In contrast to ultrasound systems, terahertz measurements can be carried out without a coupling medium and is therefore a truly contactless measurement. The possibility to measure individual layers in a multilayer stack is highly advantageous in contrast to established eddy current measurement devices. Unlike X-ray devices, terahertz radiation of common measurement systems is not harmful to biological tissue. Terahertz measurement systems have undergone a remarkable development in terms of the performance as well as in the evaluation algorithms. Increase of speed and enhancement of measurement robustness make these optically complex systems ready for industrial employment. In our contribution, we will cover the development of photonic terahertz measurement systems with a focus on terahertz layer thickness determination.
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