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Optical coherence tomography (OCT) vibrometry enables non-invasive, high-resolution measurement of tissue motion with nanometer sensitivity. However, ex vivo measurements are limited by postmortem changes, and in vivo recordings are susceptible to patient motion artifacts. Therefore, accelerating OCT vibrometry acquisition is essential for advancing both fundamental research and clinical applications. To address this challenge, we introduce multisine OCT vibrometry. Using multisine stimulation, a single OCT dataset captures displacement information across a broad frequency range. Here, we present frequency-dependent displacement data for rubber membranes and rabbit eardrums. The multisine dataset results are consistent with pure-tone validation measurements. Furthermore, the multisine datasets offer insights into the relative mobility of the rubber membrane and eardrum samples, underscoring their potential for tissue characterization and diagnosis. Our findings demonstrate that multisine OCT vibrometry reduces acquisition, processing, and visualization time without compromising accuracy. This approach enables dense OCT data collection and represents a significant advancement toward rapid, reliable clinical assessment of middle ear mechanics.

Optical coherence tomography (OCT) vibrometry is a promising tool for middle-ear mechanics, but single-frequency approaches limit efficiency and diagnostic power. We introduce multisine OCT vibrometry in a rabbit model to capture broadband, frequency-dependent eardrum vibrations acquired in a single OCT volume. Multisine data revealed that control ears had maximal umbo displacement at 1.4 kHz with an amplitude of 86 ± 11 nm (N=5). Proof-of-concept measurements were performed to highlight the diagnostic value of detecting pathology related shifts in umbo displacement using multisines. Local thinning of the eardrum by ablation decreased the frequency of maximal displacement to 1.0 kHz and resulted in an umbo displacement of 84 ± 4 nm. In contrast, perforation of the eardrum caused an overall drop in displacement amplitude across frequencies, with a maximal displacement of 34 ± 3 nm reached at 2 kHz. Additionally, the single multisine OCT volume allowed visualization of the eardrum’s displacement across the surface for all multisine tones. Ablation and perforations caused localized changes of the eardrum’s displacement at frequencies above 4 kHz. Thus, multisine OCT vibrometry holds promise for improved diagnosis and surgical planning: umbo frequency-displacement curves can distinguish between healthy and pathological ears, while spatial displacement maps reveal lesion-specific displacement patterns at high frequencies.

Loss of focus in depth due to the mismatch between the coherence gate and the focus gate is a limiting factor in the achievable high lateral resolution in optical coherence tomography (OCT). This work adapts a simplified dynamic focus method, utilising only one mechanical element to a full-field OCT configuration, and demonstrates the capability to maintain the alignment of the coherence gate and the depth of the focus gates, at sample depths of up to 4 mm while using a high numerical aperture objective lens (NA = 0.5).

This paper comprehensively demonstrates the efficiency of balanced detection in a visible optical coherence tomography instrument employing a low-noise supercontinuum laser. By using an innovative technique for digitally aligning camera pixels, we achieved a noise floor reduction of up to 12.8 dB across the entire imaging depth range, particularly near the zero optical path difference between the interferometer arms. The instrument presented here operates at a central wavelength of 590 nm. It delivers high-resolution images with a sensitivity of up to 74 dB in a single spectrometer configuration and 92.8 dB in a balanced configuration. The enhancement in image contrast is exemplified through images of an optical phantom and in-vivo images of a human thumb and nail.

In this letter, a swept-source optical coherence tomography (SS-OCT) instrument employing an innovative scanning protocol for high-speed volumetric rate imaging is demonstrated. The optical source is a tuneable laser based on a supercontinuum source pumped with femtosecond pulses, followed by a time-stretched delay fibre. The instrument is equipped with an ultra-fast lateral scanner, based on a KTN crystal, driven at 100 kHz. The paper proves the utility of combining an ultra-fast lateral scanner with an ultra-fast swept laser to provide A-scans at a repetition rate of 40 MHz and an unprecedented 3D-OCT volume acquisition rate of 400 Hz.

In this paper, a fast dual resonance akinetic opticalswept source operating at 1550 nm is demonstrated. In-stead of modulating the optical amplifier gain reportedin our previous studies, here we employ a fiber intensitymodulator as a mode-locking element. A chirped fiberBragg grating is used to provide sufficient dispersion inthe laser cavity. A tuning range of 25 nm is obtained fora sweep frequency of ~900 kHz with a 6 dB drop-off insensitivity at 2.6 mm optical path difference.

Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography Authors Gheorghe Hutiu, Virgil-Florin Duma, Dorin Demian, Adrian Bradu and Adrian Podoleanu Coordinates Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography, Metals 8(2), 117 (2018). Abstract Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents) or for parts working under harsh conditions (e.g., pipes or turbines) would benefit from a method/technique that distinguishes ductile from brittle fractures of metals—as material defects are one of the potential causes of incidents. Nowadays, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM instruments are large, expensive, time-consuming, and lab-based; hence, in situ measurements are impossible. To tackle these issues, we propose as an alternative, lower-cost, sufficiently high-resolution technique, Optical Coherence Tomography (OCT) to perform fracture analysis by obtaining the topography of metallic surfaces. Several metals have been considered in this study: low soft carbon steels, lamellar graphite cast iron, an antifriction alloy, high-quality rolled steel, stainless steel, and ductile cast iron. An in-house developed Swept Source (SS) OCT system, Master-Slave (MS) enhanced is used, and height profiles of the samples’ surfaces were generated. Two configurations were used: one where the dimension of the voxel was 1000 μm^3 and a second one of 160 μm^3—with a 10 μm and a 4 μm transversal resolution, respectively. These height profiles allowed for concluding that the carbon steel samples were subject to ductile fracture, while the cast iron and antifriction alloy samples were subjected to brittle fracture. The validation of OCT images has been made with SEM images obtained with a 4 nm resolution. Although the OCT images are of a much lower resolution than the SEM ones, we demonstrate that they are sufficiently good to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures—especially with the higher resolution MS/SS-OCT system. The investigation is finally extended to the most useful case of fatigue fracture of metals, and we demonstrate that OCT is able to replace SEM for such investigations as well

Complex master-slave for long axial range swept-source optical coherence tomography Authors Manuel J. Marques, Sylvain Rivet, Adrian Bradu, and Adrian Podoleanu Coordinates Complex master-slave for long axial range swept-source optical coherence tomography," OSA Continuum 1, 1251-1259 (2018). Abstract Using complex master-slave interferometry, we demonstrate extended axial range optical coherence tomography for two commercially available swept sources, well beyond the limit imposed by their k-clocks. This is achieved without k-domain re-sampling and without engaging any additional Mach-Zehnder interferometer providing a k-clock signal to the digitizer. An axial imaging range exceeding 17 mm with an attenuation of less than 30 dB is reported using two commercially available swept sources operating at 1050 nm and a 100 kHz repetition rate. This procedure has more than trebled the range achievable using the k-clock signal provided by the manufacturers. An analysis is presented on the impact that the digitization has on the axial range and resolution of the system.

Down-conversion en-face optical coherence tomography Authors Adrian Podoleanu, Ramona Cernat and Adrian Bradu Coordinates Down-conversion en-face optical coherence tomography," Biomed. Opt. Express 10, 772-788 (2019). Abstract We present an optical coherence tomography (OCT) method that can deliver an en-face OCT image from a sample in real-time, irrespective of the tuning speed of the swept source. The method, based on the master slave interferometry technique, implements a coherence gate principle by requiring that the optical path difference (OPD) between the arms of an imaging interferometer is the same with the OPD in an interrogating interferometer. In this way, a real-time en-face OCT image can originate from a depth in the sample placed in the imaging interferometer, selected by actuating on the OPD in the interrogating interferometer, while laterally scanning the incident beam over the sample. The generation of the en-face image resembles time domain OCT, with the difference that here the signal is processed based on spectral domain OCT. The optoelectronic processor operates down-conversion of the chirped radio frequency signal delivered by the photo-detector. The down-conversion factor is equal to the ratio of the maximum frequency of the photo-detected signal due to an OPD value matching the coherence length of the swept source, to the sweeping rate. This factor can exceed 106 for long coherence swept sources.

Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor 01 December 2022 {: .label .label-blue } New journal paper published in Materials! Authors Adrian Cioabla,Virgil-Florin Duma,Corina Mnerie,Ralph-Alexandru Erdelyi, George Mihai Dobre, Adrian Bradu, and Adrian Podoleanu Title and coordinates “[Enhanced resolution optoacoustic microscopy using a Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor, Materials 15, 8571 (2022). Abstract 3D-printed materials are present in numerous applications, from medicine to engineering. The aim of this study is to assess their suitability for an application of interest today, that of testing of 3D-printed polylactic acid (PLA)-based reactors for biogas production using anaerobic digestion. The impact of temperature, pH, and aqueous phase on the tested bioreactor is investigated, together with the effect of the gaseous phase (i.e., produced biogas). Two batches of materials used separately, one after another inside the bioreactor were considered, in a realistic situation. Two essential parameters inside the reactor (i.e., pH and temperature) were continuously monitored during a time interval of 25 to 30 days for each of the two biogas-generating processes. To understand the impact of these processes on the walls of the bioreactor, samples of 3D-printed material were placed at three levels: at the top (i.e., outside the substrate), in the middle, and at the bottom of the bioreactor. The samples were analyzed using a non-destructive imaging method, Optical Coherence Tomography (OCT). An in-house developed swept-source (SS) OCT system, master–slave (MS) enhanced, operating at a central wavelength of 1310 nm was utilized. The 3D OCT images related to the degradation level of the material of the PLA samples were validated using Scanning Electron Microscopy (SEM). The differences between the impact of the substrate on samples situated at the three considered levels inside the reactor were determined and analyzed using their OCT B-scans (optical cross-section images). Thus, the impact of the biogas-generating process on the interior of the bioreactor was demonstrated and quantified, as well as the capability of OCT to perform such assessments. Therefore, future work may target OCT for in situ investigations of such bioreactors.