Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement
Terahertz time-domain spectroscopy systems driven by monolithic mode-locked laser diodes (MLLDs) exhibit bandwidths exceeding 1 THz and a peak dynamic range that can compete with other state-of-the-art systems. Their main difference compared to fiber-laser-driven systems is their ultra-high repetiti...
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MDPI AG
2021-08-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/21/16/5389 |
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| author | Kevin Kolpatzeck Xuan Liu Lars Häring Jan C. Balzer Andreas Czylwik |
| author_facet | Kevin Kolpatzeck Xuan Liu Lars Häring Jan C. Balzer Andreas Czylwik |
| author_sort | Kevin Kolpatzeck |
| collection | DOAJ |
| description | Terahertz time-domain spectroscopy systems driven by monolithic mode-locked laser diodes (MLLDs) exhibit bandwidths exceeding 1 THz and a peak dynamic range that can compete with other state-of-the-art systems. Their main difference compared to fiber-laser-driven systems is their ultra-high repetition rate of typically dozens of GHz. This makes them interesting for applications where the length of the terahertz path may not be precisely known and it enables the use of a very short and potentially fast optical delay unit. However, the phase accuracy of the system is limited by the accuracy with which the delay axes of subsequent measurements are synchronized. In this work, we utilize an all-fiber approach that uses the optical signal from the MLLD in a Mach–Zehnder interferometer to generate a reference signal that we use to synchronize the detected terahertz signals. We demonstrate transmission-mode thickness measurements of stacked layers of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>17</mn><mspace width="0.166667em"></mspace><mi mathvariant="sans-serif">μ</mi></mrow></semantics></math></inline-formula>m thick low-density polyethylene (LDPE) films. |
| first_indexed | 2024-03-10T08:24:30Z |
| format | Article |
| id | doaj.art-855ba8d97fb84faaa5d7e9a26322c4e0 |
| institution | Directory Open Access Journal |
| issn | 1424-8220 |
| language | English |
| last_indexed | 2024-03-10T08:24:30Z |
| publishDate | 2021-08-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Sensors |
| spelling | doaj.art-855ba8d97fb84faaa5d7e9a26322c4e02023-11-22T09:38:54ZengMDPI AGSensors1424-82202021-08-012116538910.3390/s21165389Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness MeasurementKevin Kolpatzeck0Xuan Liu1Lars Häring2Jan C. Balzer3Andreas Czylwik4Chair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, GermanyChair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, GermanyChair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, GermanyChair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, GermanyChair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, GermanyTerahertz time-domain spectroscopy systems driven by monolithic mode-locked laser diodes (MLLDs) exhibit bandwidths exceeding 1 THz and a peak dynamic range that can compete with other state-of-the-art systems. Their main difference compared to fiber-laser-driven systems is their ultra-high repetition rate of typically dozens of GHz. This makes them interesting for applications where the length of the terahertz path may not be precisely known and it enables the use of a very short and potentially fast optical delay unit. However, the phase accuracy of the system is limited by the accuracy with which the delay axes of subsequent measurements are synchronized. In this work, we utilize an all-fiber approach that uses the optical signal from the MLLD in a Mach–Zehnder interferometer to generate a reference signal that we use to synchronize the detected terahertz signals. We demonstrate transmission-mode thickness measurements of stacked layers of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>17</mn><mspace width="0.166667em"></mspace><mi mathvariant="sans-serif">μ</mi></mrow></semantics></math></inline-formula>m thick low-density polyethylene (LDPE) films.https://www.mdpi.com/1424-8220/21/16/5389terahertztime-domain spectroscopymode-locked laser diodesynchronizationinterferometer |
| spellingShingle | Kevin Kolpatzeck Xuan Liu Lars Häring Jan C. Balzer Andreas Czylwik Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement Sensors terahertz time-domain spectroscopy mode-locked laser diode synchronization interferometer |
| title | Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement |
| title_full | Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement |
| title_fullStr | Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement |
| title_full_unstemmed | Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement |
| title_short | Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement |
| title_sort | ultra high repetition rate terahertz time domain spectroscopy for micrometer layer thickness measurement |
| topic | terahertz time-domain spectroscopy mode-locked laser diode synchronization interferometer |
| url | https://www.mdpi.com/1424-8220/21/16/5389 |
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