Mid-infrared (mid-IR) hyperspectral imaging is of great practical interest in various fields of science and industry due to its ability to provide spatially resolved label-free chemical information. However, the widespread adoption and advancement of mid-IR hyperspectral imaging are hindered by high costs and the specification lag of mid-IR focal plane arrays. In this contribution, we propose a method to circumvent this problem and thus demonstrate a solution for mid-IR hyperspectral imaging through the use of a single-pixel imaging paradigm involving a mid-IR enhanced digital micro-mirror device (DMD); as a light source, a high-brightness mid-IR supercontinuum source is exploited. The developed mid-IR hyperspectral microscope enables the acquisition of hyperspectral cubes with dimensions of 64x64 pixels and a spectral resolution of 120 nm accomplished within approximately 450 ms. The developed laser-based system provides rapid mid-IR hyperspectral imaging with a programmable scalable field of view and variable spatial resolution. Thus, this solution represents a cost-effective alternative to state-of-the-art mid-infrared imagers.
In this paper, we present a Wavefront Division (WD) Fourier domain Swept Source Optical Coherence Tomography (SS-OCT) configuration. The presented WD-SS-OCT configuration has two key features that are discussed in this contribution. First, there is the possibility of variable splitting and flexible adjustment of the splitting ratio between the sample and the reference. This enables an adaptation to differing reflective and scattering features of various samples. The second feature is related to the increased throughput of the interferometer design. The use of polarization optics makes it possible to almost eliminate back-reflection losses completely to the source (up to 50% of the intensity in standard amplitude division-based OCT). WD-OCT configuration has its challenges compared to conventional OCT systems based on amplitude splitting. Nevertheless, the proposed design has also specific options and flexibilities that are worth to be shared with the OCT community.
Mid-infrared (MIR) hyperspectral imaging allows for spatially resolved chemical imaging, making it highly attractive for many branches. However, expensive MIR array detector technology limits its application. Here, we present a cost-effective MIR hyperspectral detection system based on a single-pixel imaging approach using an MIR-enhanced digital micromirror device. For illumination an MIR supercontinuum source was used completing the MIR hyperspectral microscope. It allows acquiring hyperspectral cubes with 64x64 pixels and 120 nm spectral resolution within ≈450 ms. The developed microscope provides fast MIR hyperspectral imaging with a tunable field of view and tunable spatial resolution based on cost-effective components. Thus, it will bring hyperspectral imaging into new fields and increase sample throughput due to its fast-imaging speed.
We provide an overview of optical coherence tomography (OCT) applied in the field of non-destructive testing (NDT). The applications include examples for structural polymer material testing at mesoscopic size scale, visualizing and validating internal sub-surface micro-defects, or characterizing the coating and bonding quality in multilayer samples. Furthermore, dynamical processes observed by OCT in their temporal progress can be demonstrated in the context of NDT as well as multimodal settings for gaining structural and specific insights on the materials tested. We will also regard the challenges for performing dimensional measurements and optical metrology by OCT imaging. In addition, novel developments and trends at illumination and detection sites will be discussed as essential components and requirements for the progress in OCT technology. This includes newly accessible spectral ranges under the view point of sensing as well as adaptable learning tools under the view point of data and image processing, which will round off the topic.
Novel types of supercontinuum sources radiating in the infrared (IR) spectral region provide ultra-broadband spectral coverage and maintain distinctive laser-like properties of emission such as brightness, spatial coherence and high power. Being a perfectly suitable light source for mid-infrared optical coherence tomography (OCT) and spectroscopy, supercontinuum sources initiated a significant amount of recent developments in these fields and promise to be a gamechanging factor in the nearest future. In this paper, we exhibit a simple, optimized and relatively cost-effective system operating in near and mid-infrared ranges and combining OCT and co-registered IR spectroscopy. The performance of the OCT modality of the setup is evaluated with respect to the sensitivity and roll-off. Due to reduced scattering inherited with the new spectral window, we achieve the enhancement in the penetration depth in artificial paintings, ceramics and pottery. Furthermore, the hyperspectral data is used to supplement structural information and access to the chemical composition of the sample. The gained results reveal the potential of the multimodal system for non-destructive testing, art and cultural objects diagnosis.
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