Optical coherence tomography for laser transmission joining processes in polymers and semiconductors

Laser transmission welding applications become wide spread technology in joining transparent and turbid materials. The requirement of higher throughputs and lesser rejects support the need of alternative methods to commonly used machine vision or temperature measurements. Optical coherence tomography delivers the opportunity to qualitatively assess transmission welding seems and welding spots even in three dimensions. Fourier Domain Mode Lock Lasers (FDMLs) used in OCT enable high throughput by high sweep rates. Preliminary results of OCT used for qualitatively assessment of laser transmission welded polymers and fiber reinforced plastics are shown as well as first approaches of using OCT in a silicon chip bonding process

Laser-based molecular delivery and its applications in plant science

Lasers enable modification of living and non-living matter with submicron precision in a contact-free manner which has raised the interest of researchers for decades. Accordingly, laser technologies have drawn interest across disciplines. They have been established as a valuable tool to permeabilize cellular membranes for molecular delivery in a process termed photoinjection. Laser-based molecular delivery was first reported in 1984, when normal kidney cells were successfully transfected with a frequency-multiplied Nd:YAG laser. Due to the rapid development of optical technologies, far more sophisticated laser platforms have become available. In particular, near infrared femtosecond (NIR fs) laser sources enable an increasing progress of laser-based molecular delivery procedures and opened up multiple variations and applications of this technique. This review is intended to provide a plant science audience with the physical principles as well as the application potentials of laser-based molecular delivery. The historical origins and technical development of laser-based molecular delivery are summarized and the principle physical processes involved in these approaches and their implications for practical use are introduced. Successful cases of laser-based molecular delivery in plant science will be reviewed in detail, and the specific hurdles that plant materials pose will be discussed. Finally, we will give an outlook on current limitations and possible future applications of laser-based molecular delivery in the field of plant science

Wavefront sensorless adaptive optics for optical coherence tomography guided femtosecond laser surgery in the posterior eye

Surgery with fs-laser in the posterior part of the eye could be useful for separation of tractional epiretinal membrane and vitreous floaters treatment. However, focus degradation occurs near the retina due to induced aberrations by cornea and lens. To overcome this issue, adaptive optics with wavefront sensor and wavefront modulator can be utilized. We demonstrate an alternative concept for image guided femto second laser (fs-laser) surgery in the posterior eye with wavefront sensorless adaptive optics (WFSLAO). Our laboratory setup consists of an 800 nm fs-laser and a superluminescent diode (SLD) with 897.2 nm central wavelength. The SLD is used for optical coherence tomography (OCT) whereby the light for the OCT sample arm and the fs-laser share the same optical path which contains a deformable mirror, scanner and focusing optics. Energy calibrated photodiodes are used to measure the threshold energy for a laser induced optical breakdown inside a water filled chamber that acts as simple eye model. OCT image based metrics were used to determine a set of Zernike polynomials that describe a near optimal deformable mirror state. Such a mirror state improved OCT resolution and at the same time lowered the required fs-laser energy for a laser induced optical breakdown inside the eye model substantially. © COPYRIGHT SPIE

Characterization and digital aberration correction of a hyperspectral imaging system for plant disease detection

Hyperspectral imaging is a key technology for monitoring agricultural crops and vegetation. It can be used for health estimation and the early detection of disease symptoms in plants. This can help to reduce the use of pesticides by allowing targeted and early intervention. Cost-efficient hyperspectral imaging systems are necessary to meet the increasing demand for monitoring techniques for agricultural products. These systems usually suffer from sub-optimal image quality. Here we present a digital aberration correction for hyperspectral image data. Copyright 2023 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

Concept for high speed vocal cord imaging with swept-source optical coherence tomography

Optical coherence tomography (OCT) enables non-invasive depth-resolved investigation of laryngeal tissue. However, with conventional systems, OCT cross-sectional images of vibrating vocal cords always suffer from motion artifacts. This is the case even at low phonation frequencies of about 100 Hz. Motion artifacts of predictable repetitive movements can be avoided with carefully timed acquisitions. Irregular, non-repetitive movements, e.g. disturbed vocal cord vibration caused by laryngeal disorders, require different strategies, such as the use of high frame rates. We present a novel concept for dynamic vocal cord imaging with a high speed 1.6 MHz swept-source OCT system. Due to the high image rate, a graphics processing unit (GPU) based signal processing software has been developed in order to obtain real time OCT images. To demonstrate the feasibility of our approach on vibrating samples, we present a laboratory setup which includes a MHz swept source for OCT. To enable the transfer of our setup to clinical applications a concept for a curved rigid laryngoscope design, integrating the optical components for high-speed OCT, is proposed. Copyright © 2019 SPIE

Development of a portable and low-cost OCT system for horticultural research

Optical coherence tomography (OCT), a non-contact, non-destructive imaging technique, is becoming a popular tool in phytophotonics, helping to address research questions in plant biology and horticulture. However, the stationary nature of typical OCT systems compromises its non-destructive advantage since plants often need to be dissected for an analysis with a laboratory OCT system. Here we present a portable, low-cost OCT system that enables in-situ measurements of plants. We outline technical challenges encountered during the development and showcase initial measurements of different plant tissues. Copyright 2024 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

Ultraschnelle optische Kohärenztomographie an humanen Stimmlippen

Die optische Kohärenztomographie (OCT, engl. optical coherence tomography) ist ein nicht-invasives, dreidimensionales Bildgebungsverfahren, das hochauflösende Schnittbilder von biologischem Gewebe erstellt. Dabei sind Bildgebungstiefen von mehreren hundert Mikrometern in Gewebe bei optischen Auflösungen im ein- bis zweistelligen Mikrometerbereich typisch. Das Haupteinsatzfeld der OCT ist die Ophthalmologie, in der sie vor allem zur Diagnose von netzhautbetreffenden Augenerkrankungen eingesetzt wird. Neben dieser Hauptanwendung werden im biomedizinischen Bereich weitere Einsatzmöglichkeiten der OCT erforscht. Insbesondere endoskopische OCT-Anwendungen zeigen großes Potenzial, etablierte Diagnosemethoden wie die Entnahme von Gewebeproben für histologische Untersuchungen zu ergänzen oder in bestimmten Fällen zu ersetzen. Speziell bei der Diagnose von Stimmlippenerkrankungen bietet OCT die Möglichkeit, Biopsien zu ersetzen, welche zu Narbenbildungen und folglich zu dauerhaften Veränderungen der Stimme führen können. Seit einigen Jahren sind durchstimmende Lichtquellen verfügbar, die eine ultraschnelle OCT-Bildgebung mit über einer Million axialer Linienprofile pro Sekunde ermöglichen. Solch eine schnelle OCT-Bildgebung wird als MHz-OCT bezeichnet. Diese Arbeit befasst sich mit der Entwicklung eines starren, gekrümmten Endoskops für die Bildgebung von Stimmlippen mittels MHz-OCT. Anhand durchgeführter Optiksimulationen wurde ein Strahlengangdesign entwickelt, das auf handelsüblichen Linsen basiert. Diese Linsen wurden in ihrem Durchmesser angepasst und in ein gekrümmtes Endoskopgehäuse integriert. Das Gehäuse wurde mittels Rapid-Prototyping-Verfahren aus einem biokompatiblen Material (PolyJet MED610 von Stratasys Ltd.) gefertigt. Mit dem umgesetzten MHz-OCT-System können Schnittbilder mit einer Rate von über 3000 Hz erfasst werden. Diese hohe Bildrate eignet sich für die Darstellung dynamischer Prozesse, wie etwa der Vibration der Stimmlippen während der Phonation. Zur Erzeugung der Bilddaten müssen die erfassten OCT-Rohdaten zunächst verarbeitet werden. Dafür wurde eine Softwarelösung entwickelt, die OCT-Signalverarbeitung und Visualisierung auf einer Grafikkarte durchführt. Ein Plugin-Konzept ermöglicht die Integration zusätzlicher Hard- und Softwaremodule. Unter Verwendung dieses Konzepts wurde eine Arbeitsabstandsregelung realisiert, welche notwendig ist, da die Position der Stimmlippen interindividuell variiert. Die anatomisch bedingten Unterschiede können mehrere Zentimeter betragen, wohingegen die OCT-Bildgebungstiefe in Luft lediglich im Millimeterbereich liegt. Die Arbeitsabstandsregelung erfolgt durch Anpassung der Fokusposition des OCT-Strahls mittels einer Flüssiglinse sowie durch Einstellung der OCT-Referenzarmlänge durch einen motorisierten Linearverfahrtisch. Eine Herausforderung, die dabei gelöst wurde, ist die Umsetzung einer automatisierten Detektion der Probe, die zwischen regulärem Probensignal und Spiegelartefakt unterscheiden kann. Unter Spiegelartefakt versteht man hierbei das Probensignal, welches entsteht, wenn die Probe außerhalb des OCT-Bildbereichs gerät und infolgedessen umgekehrt dargestellt wird. Um kleine, hochfrequente Bewegungen, wie sie z. B. durch Handtremor beim Halten des Endoskops hervorgerufen werden können, auszugleichen, wurde eine digitale Bildstabilisierung implementiert. Diese hält die im Schnittbild detektierte Probenoberfläche auf einer festgelegten Höhe im Ausgabefenster, indem das Schnittbild entgegen der ungewollten Verschiebung versetzt wird. Im Vergleich zu bisherigen, aus der Literatur bekannten, OCT-Laryngoskopen ist das System dieser Arbeit das erste mit einer MHz-OCT-Bildgebung und einer automatisierten Arbeitsabstandsregelung mit einer Probendetektion, die reguläres Probensignal und Spiegelartefakt unterscheiden kann.Optical coherence tomography (OCT) is a non-invasive, three-dimensional imaging technique that produces high-resolution cross-sectional images of biological tissue. It typically achieves imaging depths of several hundred micrometers in tissue, with optical resolutions ranging from single to double-digit micrometers. While ophthalmology remains the primary application for OCT, especially in diagnosing retina-related eye diseases, there is growing interest in its broader biomedical applications. Notably, endoscopic OCT applications offer promising potential, either complementing or, in specific cases, replacing traditional diagnostic methods such as tissue biopsy for histological analysis. Particularly in diagnosing vocal fold disorders, OCT could substitute for biopsies, which might lead to scar formation, potentially causing a permanent alteration of the voice. For several years, swept-source lasers have been available, enabling ultra-fast OCT imaging with over a million axial line profiles per second. This high-speed OCT imaging is termed MHz-OCT. This thesis focuses on the design and development of a rigid, curved endoscope for imaging the vocal folds using MHz-OCT. Based on optical simulations, a design utilizing commercially available lenses was developed. The diameters of these lenses were adjusted to fit within a curved endoscope housing. This housing was produced from a biocompatible material (PolyJet MED610 by Stratasys Ltd.) using rapid prototyping methods. The implemented MHz-OCT system enables the acquisition of cross-sectional images at rates exceeding 3000 Hz. These high acquisition rates are beneficial for capturing dynamic processes, such as the vibration of vocal folds during phonation. Acquired OCT raw data must first be processed to generate the corresponding image data. For this purpose, a software tool was designed to perform OCT signal processing and visualization on a single graphics card. A modular plugin architecture was incorporated to allow for the integration of additional hardware and software components. Using this concept, a working distance control was implemented, which is necessary due to the interindividual variation in the position of the vocal cords. The anatomical differences can amount to several centimeters, whereas the OCT imaging depth in air is limited to the millimeter range. The working distance is adjusted by modifying the focus position of the OCT beam with a liquid lens and by altering the OCT reference arm length using a motorized linear translation stage. One challenge that was overcome involved implementing an automated sample detection system capable of distinguishing between a regular sample signal and a mirror artifact. A mirror artifact occurs when the sample moves out of the OCT imaging range, resulting in an image that is displayed upside-down. To compensate for small, high-frequency movements, such as hand tremors during endoscope handling, digital image stabilization was integrated. This ensures that the detected sample surface in the cross-sectional image remains at a set height within the output window by adjusting the cross-sectional image to counteract any unintended movement. In comparison to OCT-laryngoscopes previously published in the literature, the system presented in this thesis is the first to incorporate MHz-OCT imaging and an automated working distance control with a sample detection capability that can distinguish between regular sample signals and mirror artifacts

OCT wavenumber calibration with simple reference arm modification

FD-OCT systems with non-uniform wavenumber sampling require calibration and resampling routines to achieve optimal axial resolution. We present a simple calibration procedure and provide all necessary algorithmic components for wavenumber resampling

Laser-based Space Debris Removal - Laser-induced momentum generation on true scale debris-like targets

Laser-based space debris removal concepts have been around for decades now. Nevertheless, practical implementation is still connected to great technological risks. Most of the concepts plan to utilize the laser ablative process at the target. To investigate this common aspect in detail and to reduce the risk of misleadingly extrapolating parameters, we now experimentally investigated the generation of impulse under realistic conditions as to be expected in a real space scenario. An Nd:YAG based, 10 ns pulsed MOPA laser system providing a pulse energy of 80 J was weakly focused to a diameter of 3 cm onto debris-like targets with different sizes, shapes and materials. The target masses ranged between 1 g to 3 g, indeed representing dangerous objects, and were in free fall within a vacuum during single pulse irradiation. High speed 3D-tracking was applied to deduce the kinetic properties induced by the ablation process. Finally, the data was compared to raytracing based simulation results. Differences between materials and mechanical dynamics are discussed

Experimental verification of high energy laser-generated impulse for remote laser control of space debris

Walking along a beach one may notice debris being washed ashore from the vast oceans. Then, turning your head up at night you even might noticed a shooting star or a bright spot passing by. Chances are, that you witnessed space debris, endangering future space flight in lower earth orbit. If it was possible to turn cm-sized debris into shooting stars the problem might be averted. Unfortunately, these fragments counting in the 100 thousands are not controllable. To possibly regain control we demonstrate how to exert forces on a free falling debris object from a distance by ablating material with a high energy ns-laser-system. Thrust effects did scale as expected from simulations and led to speed gains above 0.3 m/s per laser pulse in an evacuated micro-gravity environment