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Process control and quality assurance in remote laser beam welding by optical coherence tomography
摘要： Remote laser beam welding significantly outperforms conventional joining techniques in terms of flexibility and productivity. This process benefits in particular from a highly focused laser radiation and thus from a well-defined heat input. The small spot sizes of high brilliance laser beam sources, however, require a highly dynamic and precise positioning of the beam. Also, the laser intensities typically applied in this context result in high process dynamics and in demand for a method to ensure a sufficient weld quality. A novel sensor concept for remote laser processing based on optical coherence tomography (OCT) was used for both quality assurance and edge tracking. The OCT sensor was integrated into a 3D scanner head equipped with an additional internal scanner to deflect the measuring beam independently of the processing beam. With this system, the surface topography of the process zone as well as the surrounding area can be recorded. Fundamental investigations on aluminum, copper, and galvanized steel were carried out. Initially, the influence of the material, the angle of incidence, the welding position within the scanning field, and the temperature on the OCT measuring signal were evaluated. Based on this, measuring strategies for edge tracking were developed and validated. It was shown that orthogonal measuring lines in the advance of the process zone can reliably track the edge of a fillet weld. By recording the topography in the trailing area of the process zone, it was possible to assess the weld seam quality. Comparing the results to microscopic measurements, it was shown that the system is capable of clearly identifying characteristic features of the weld seam. Also, it was possible to observe an influence of the welding process on the surface properties in the heat-affected zone, based on the quality of the measuring signal.
关键词： inline quality assurance,optical coherence tomography,remote laser beam welding,process control
更新于2025-11-28 14:24:20
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Inline weld depth measurement for high brilliance laser beam sources using optical coherence tomography
摘要： As a result of the rapidly growing importance of applications in electro mobility that require a precisely defined laser weld depth, the demand for inline process monitoring and control is increasing. To overcome the challenges in process data acquisition, this paper proposes the application of a novel sensor concept for deep penetration laser beam welding with high brilliance laser sources. The experiments show that optical coherence tomography (OCT) can be used to measure the weld depth by comparing the distance to the material surface with the distance to the keyhole bottom measured by the sensor. Within the presented work, the measuring principle was used for the first time to observe a welding process with a highly focused laser beam source. First, a preliminary experimental study was carried out to evaluate the influence of the angle of incidence, the material, and the weld joint geometry on the quality of the sensor signal. When using a multimode fiber laser with a focus diameter of 320 μm, the measurements showed a distinct behavior for aluminum and copper. The findings about the measurement signal properties were then applied to laser beam welding with a single-mode fiber laser with a spot diameter of only 55 μm. The spot diameter of the OCT measuring beam was about 50 μm and thus only slightly smaller than that of the single-mode processing beam. A wide variety of tests were carried out to determine the limits of the measurement procedure. The results show that the application of OCT allows inline monitoring of the weld depth using both a multimode and a highly focused single-mode laser beam. In addition, various influences on the signal were identified, e.g., the material-specific melt pool dynamics as well as several characteristic reflection and absorption properties.
关键词： high brilliance laser beam sources,weld depth measurement,optical coherence tomography,laser beam welding
更新于2025-11-28 14:24:20
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<i>In vivo</i> detection of endotracheal tube biofilms in intubated critical care patients using catheter-based optical coherence tomography
摘要： The formation of biofilms in the endotracheal tubes (ETTs) of intubated patients on mechanical ventilation is associated with a greater risk of ventilator-associated pneumonia (VAP) and death. New technologies are needed to detect and monitor ETTs in vivo for the presence of these biofilms. Longitudinal OCT imaging was performed in mechanically ventilated subjects at 24 hr intervals until extubation to detect the formation and temporal changes of in vivo ETT biofilms. OCT-derived attenuation coefficient images were used to differentiate between mucus and biofilm. Extubated ETTs were examined with optical and electron microscopy, and all imaging results were correlated with standard-of-care clinical test reports. OCT and attenuation coefficient images from 4 subjects were positive for ETT biofilms and were negative for 2 subjects. The processed and stained extubated ETTs and clinical reports confirmed the presence/absence of biofilms in all subjects. Our findings confirm that OCT can detect and differentiate between biofilm-positive and biofilm-negative groups (p < 10-5). OCT image-based features may serve as biomarkers for direct in vivo detection of ETT biofilms and help drive investigation of new management strategies to reduce the incidence of VAP.
关键词： attenuation coefficient image,endotracheal tube,biofilm,optical coherence tomography,ventilator-associated pneumonia
更新于2025-11-21 11:24:58
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Role of interface potential barrier, Auger recombination and temporal coherence in In <sub/>0.5</sub> Ga <sub/>0.5</sub> As/GaAs quantum dot-based p-i-n light emitting diodes
摘要： In this work, we investigate the mechanisms that control the electroluminescence from p-i-n heterostructures containing self-assembled In0.5Ga0.5As quantum dots embedded inside a GaAs/Al0.3Ga0.7As quantum well as a function of temperature and applied bias. Our results reveal that the carrier dynamics at the interface between the quantum dot and the quantum well play a crucial role in the electroluminescence emission. At low temperatures, two distinct emission bands are observed. Initially at low bias current, we observe broad emissions from the quantum wells and wetting layers. Another dominant and sharp emission at lower energy arises from the quantum dots, but only at higher bias currents. We discuss how a potential barrier between the quantum dots and quantum well can control the density of injected carriers undergoing optical recombination. We have also investigated the role of carrier capture and escape, quantum-confined stark effect and band-filling effects in the electroluminescence emission. In addition, we demonstrate how measurements of temporal coherence of individual spectral peaks, can detect the presence of Auger recombination in quantum dots under high injection currents. Interestingly, a significant increase in the temporal coherence of quantum dot emissions is observed, which could be due to a decrease in Auger recombination with increasing temperature.
关键词： quantum dots,Auger recombination,electroluminescence,coherence
更新于2025-11-14 17:28:48
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Microvascular Capillary Plexus Findings of Commotio Retinae on Optical Coherence Tomography Angiography
摘要： Optical coherence tomography (OCT) and histopathology features of commotio retinae (CR) have been established, but alterations of the microvascular macular capillary plexus on OCT angiography (OCTA) has not been previously studied. We present a 46-year-old man who sustained a tennis ball injury to the right eye with visual acuity reduction to 20/30 and grey-white deep macular discoloration, suggestive of CR. Spectral-domain OCT (SD-OCT) showed increased reflectivity and thickness of the ellipsoid zone (junction of photoreceptor inner and outer segments). OCTA revealed no apparent microvascular alterations (right versus left eye) in the foveal avascular zone superficial (0.42 vs. 0.43 mm2) and deep (0.45 vs. 0.44 mm2), superficial foveal capillary density (34.1 vs. 32.6%), and superficial parafoveal capillary density (55.2 vs. 52.2%). Deep macular capillary plexus and choriocapillaris were qualitatively comparable between the two eyes. At 2 months’ follow-up, SD-OCT had normalized. CR is characterized by disruption of the ellipsoid zone without detectable alteration of the capillary plexuses.
关键词： Optical coherence tomography angiography,Commotio retinae,Berlin’s edema,Spectral-domain optical coherence tomography,Traumatic maculopathy
更新于2025-09-23 15:23:52
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Multimodal imaging and treatment of Purtscher-like retinopathy
摘要： A 52-year-old patient with multiple cardiovascular risk factors referred for unilateral, acute, and painless visual loss. In the fundoscopic image there was significant papillary inflammation with tortuosity at this level and hemorrhages. Ophthalmological examination showed papillary inflammation, macular edema, and involvement in retinal inner layers. The control fluorescein angiography and optical coherence tomography angiography showed areas of central and peripheral ischemia. Given the clinical findings and background of the patient, the diagnosis of Purtscher-like retinopathy was reached and treatment with intravitreal dexamethasone was decided. Purtscher-like retinopathy is a rare entity that occurs in patients with multiple systemic pathologies, but without a traumatic background, which differentiates it from Purstcher's retinopathy. The diagnosis and early intervention are important in the prognosis. There are no therapeutic protocols, but good results have been obtained with intravitreal therapy with dexamethasone.
关键词： Purtscher flecken,Purtscher-like retinopathy,Purtscher retinopathy,Optical coherence tomography angiography,Optical coherence tomography
更新于2025-09-23 15:23:52
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Characterization of Abnormal Optic Nerve Head Morphology in Albinism Using Optical Coherence Tomography
摘要： PURPOSE. To characterize abnormalities in three-dimensional optic nerve head (ONH) morphology in people with albinism (PWA) using spectral-domain optical coherence tomography (SD-OCT) and to determine whether ONH abnormalities relate to other retinal and clinical abnormalities. METHODS. Spectral-domain OCT was used to obtain three-dimensional images from 56 PWA and 60 age- and sex-matched control subjects. B-scans were corrected for nystagmus-associated motion artefacts. Disc, cup, and rim ONH dimensions and peripapillary retinal nerve fiber layer (ppRNFL) thickness were calculated using Copernicus and ImageJ software. RESULTS. Median disc areas were similar in PWA (median ? 1.65 mm2) and controls (1.71 mm2, P ? 0.128), although discs were significantly elongated horizontally in PWA (P < 0.001). In contrast, median optic cup area in PWA (0.088 mm2) was 23.7% of that in controls (0.373 mm2, P < 0.001), with 39.4% of eyes in PWA not demonstrating a measurable optic cup. This led to significantly smaller cup to disc ratios in PWA (P < 0.001). Median rim volume in PWA (0.273 mm3) was 136.6% of that in controls (0.200 mm3). The ppRNFL was significantly thinner in PWA compared with controls (P < 0.001), especially in the temporal quadrant. In PWA, ppRNFL thickness was correlated to ganglion cell thickness at the central fovea (P ? 0.007). Several ONH abnormalities, such as cup to disc ratio, were related to higher refractive errors in PWA. CONCLUSIONS. In PWA, ocular maldevelopment is not just limited to the retina but also involves the ONH. Reduced ppRNFL thickness is consistent with previous reports of reduced ganglion cell numbers in PWA. The thicker rim volumes may be a result of incomplete maturation of the ONH.
关键词： albinism,optic nerve head,optical coherence tomography
更新于2025-09-23 15:23:52
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Fusion of Multi-Temporal Interferometric Coherence and Optical Image Data for the 2016 Kumamoto Earthquake Damage Assessment
摘要： Earthquakes are one of the most devastating types of natural disasters, and happen with little to no warning. This study combined Landsat-8 and interferometric ALOS-2 coherence data without training area techniques by classifying the remote sensing ratios of specific features for damage assessment. Waterbodies and highly vegetated areas were extracted by the modified normalized difference water index (MNDWI) and normalized difference vegetation index (NDVI), respectively, from after-earthquake images in order to improve the accuracy of damage maps. Urban areas were classified from pre-event interferometric coherence data. The affected areas from the earthquake were detected with the normalized difference (ND) between the pre- and co-event interferometric coherence. The results presented three damage types; namely, damage to buildings caused by ground motion, liquefaction, and landslides. The overall accuracy (94%) of the confusion matrix was excellent. Results for urban areas were divided into three damage levels (e.g., none–slight, slight–heavy, heavy–destructive) at a high (90%) overall accuracy level. Moreover, data on buildings damaged by liquefaction and landslides were in good agreement with field survey information. Overall, this study illustrates an effective damage assessment mapping approach that can support post-earthquake management activities for future events, especially in areas where geographical data are sparse.
关键词： damage assessment,Landsat-8,ALOS-2 interferometric coherence,urban damage area,liquefaction,landslides,Kumamoto earthquake
更新于2025-09-23 15:23:52
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Retinal vascular density evaluated by optical coherence tomography angiography in macular telangiectasia type 2
摘要： Purpose To evaluate the retinal and choroidal vascular changes through optical coherence tomography angiography (OCTA) in patients with macular telangiectasia type 2 (MacTel 2). Methods Our study included 20 patients (40 eyes) with MacTel 2, and age-matched and sex-matched 18 subjects (36 eyes) in the control group. Fundus color photographs, fundus autofluorescence, fundus fluorescein angiography, spectral-domain optical coherence tomography and OCTA were performed. Foveal vascular density and parafoveal vascular density (PFVD), and foveal retinal thickness and parafoveal retinal thickness, choroidal thickness (CT) and retinal ganglion cell–inner plexiform layer (GCIPL) were compared between MacTel 2 patients and normal age-matched controls. Results The retinal whole vascular density and PFVD of the deep plexus were significantly lower in patients with MacTel 2 than that of the control group (56.93% vs. 58.54%, p = 0.003; and 60.38% vs. 61.66%, p = 0.045). The foveal avascular zone (FAZ) of the deep plexus was significantly enlarged in patients with MacTel 2 than that of the control group (0.44 vs. 0.36, p = 0.009). There was a positive and statistically significant correlation between the FAZ of the superficial and deep plexus and CT in patients with MacTel 2. There was a positive and statistically significant correlation between retinal whole, parafoveal temporal quadrant vascular density of the superficial and deep plexus and GCIPL thickness in patients with MacTel 2. Conclusions Our study demonstrated that important retinal vascular density and FAZ changes in MacTel 2 occur in the deep capillary plexus of the retina.
关键词： Macular telangiectasia type 2,Vascular density,Choroidal thickness,Retinal ganglion cell–inner plexiform layer,Optical coherence tomography angiography
更新于2025-09-23 15:23:52
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Non-ionized, High-resolution Measurement of Internal and Marginal Discrepancies of Dental Prosthesis Using Optical Coherence Tomography
摘要： An internal and marginal fit between prosthesis and abutment are important factors of the durability of dental prosthesis. In this study we have proposed the use of swept-source optical coherence tomography (SS-OCT) as a novel application for non-ionized and high-resolution measurements of internal and marginal discrepancies at anatomically critical four points, such as occlusal, angle, axial, and margin during prosthesis attachment. A tooth model was fabricated by 3D printing technique and the dental prosthesis was designed using dental CAD software. The cross-sectional images along with intensity peak profile analysis of the sample were acquired using OCT system for measurements of fit. The demonstrated qualitative and quantitative evaluations can be well-utilized for assessment of the internal and marginal fit of dental prosthesis.
关键词： Intensity analysis,Dental prosthesis,Internal and marginal fit,Swept-source optical coherence tomography
更新于2025-09-23 15:23:52