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arXiv · 2312.02408

Mid-infrared optical coherence tomography with MHz axial line rate for real-time non-destructive testing

Satoko Yagi·Takuma Nakamura·Kazuki Hashimoto·Shotaro Kawano·Takuro Ideguchi
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Abstract

Non-destructive testing (NDT) is crucial for ensuring product quality and safety across various industries. Conventional methods such as ultrasonic, terahertz, and X-ray imaging have limitations in terms of probe-contact requirement, depth resolution, or radiation risks. Optical coherence tomography (OCT) is a promising alternative to solve these limitations, but it suffers from strong scattering, limiting its penetration depth. Recently, OCT in the mid-infrared (MIR) spectral region has attracted attention with a significantly lower scattering rate than in the near-infrared region. However, the highest reported A-scan rate of MIR-OCT has been 3 kHz, which requires long data acquisition time to take an image, unsatisfying industrial demands for real-time diagnosis. Here, we present a high-speed MIR-OCT system operating in the 3-4 um region that employs the swept-source OCT technique based on time-stretch infrared spectroscopy. By integrating a broadband femtosecond MIR pulsed laser operating at a repetition rate of 50 MHz, we achieved an A-scan rate of 1 MHz with an axial resolution of 11.6 um and a sensitivity of 55 dB. As a proof-of-concept demonstration, we imaged the surface of substrates covered by highly scattering paint coatings. The demonstrated A-scan rate surpasses previous state-of-the-art by more than two orders of magnitude, paving the way for real-time NDT of industrial products, cultural assets, and structures.

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Satoko Yagi, Takuma Nakamura, Kazuki Hashimoto, Shotaro Kawano, Takuro Ideguchi. 2023-12-05. Mid-infrared optical coherence tomography with MHz axial line rate for real-time non-destructive testing. https://doi.org/10.1063/5.0202019

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