Kilohertz Pixel-Rate Multilayer Terahertz Imaging of Subwavelength Coatings

• Published in: Applied sciences Vol. 12; no. 10; p. 4964
• Main Authors: Molter, Daniel, Ellenberger, Kim-Sophie, Klier, Jens, Duran, Stefan, Jonuscheit, Joachim, von Freymann, Georg, Vieweg, Nico, Deninger, Anselm
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-05-2022
• Subjects: Algorithms; Aluminum; Disks; ECOPS; Laser applications; Lasers; layer thickness measurement; Multilayers; optical sampling; Pixels; Radiation; Sampling methods; Simulation; Spectroscopy; terahertz; terahertz imaging; Thickness; ultrafast terahertz measurements; Waveforms
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app12104964

The acquisition speed of terahertz time-domain spectroscopy systems has undergone a significant improvement in recent years. With the development of dual-laser-based sampling techniques such as ASOPS or ECOPS, waveform acquisition rates in the kilohertz range have become feasible. Here, we present measurements of sub-wavelength layers in multilayer systems at a rate of 1.6 kHz, where the individual layer thicknesses are analyzed in real time. For demonstration, we image layers on metallic and non-metallic disks with a 300 mm diameter, acquiring 240,000 pixels in only 2.5 min. By combining a rotation of the samples with a linear translation of the measurement head, we maximize the measurement yield. Owing to a “single-shot” (625 µs) dynamic range of 40 dB and a bandwidth above 3 THz of the ECOPS system, we achieve sub-micron repeatability for each layer.