This PDF file contains the front matter associated with SPIE Proceedings Volume 12170, including the Title Page, Copyright information, Table of Contents, and Conference Committee list.

There are numerous dental conditions that can appear in the human mouth, from bone diseases like periodontitis or bone loss produced by a massive infection, to common issues like dental cavities. We explored the possible range of dental (and associated bone) conditions using Optical Coherence Tomography (OCT) versus the gold standard of radiological investigations [Erdelyi R.A., Duma V.-F., et al, Materials 13, 4825, 2020]. Clinical and imaging investigations have been performed on real-life patients. Advantages and limitations of using these two imaging techniques were deduced, based on the fact that OCT has better resolution than radiographs (2 to 10 μm versus 75 to 150 μm, respectively), while radiography can perform a complete image of the entire mouth, in contrast to OCT, which has a limited penetration, of only 1 to 2 mm in tooth or soft tissue. The analyses of a range of dental conditions with both techniques clarified when it is better to choose a specific method: (i) for bone diseases, radiographs are more appropriate because they provide images of the entire mouth in one exposure and 3D images of dental conditions; (ii) OCT can spot small cavities in early stages, while radiographs cannot; (iii) measurements performed on cavities spotted with both imaging techniques proved that OCT can provide accurate dimensions, with high contrast and contrast-to-noise ratio. Thus, a classification of each of the two types of imaging techniques for each possible dental condition was obtained. A complementarity of OCT and radiography for investigations in dentistry was concluded.

We demonstrate our latest work towards a red-emitting semiconductor membrane external-cavity surface-emitting laser (MECSEL) for applications in OCT. This light source technology employs both a near-diffraction limited beam profile (M² ≥ 1.05) and a broad tuning range at tailorable emission wavelength. Due to their potential for mass production, combined with the usage of broadly available CMOS-sensors as detector units, OCT imaging device costs can be reduced to a significant amount, while delivering state-of-the-art image quality.

The quantum states of the Kapitza pendulum are investigated in the framework of the effective potential obtained by the method of averaging over fast oscillations. An analytical estimate of the energy spectrum of stabilized states is given using a model potential. For the lowest states of the inverted pendulum, an expression is obtained for the spectrum in the form of the energies of a harmonic oscillator, refined according to the perturbation theory. Tunneling corrections to the energies of resonance states in double-well effective potential are found. The results of calculations of the structure of vibrational and rotational spectra of the Kapitza pendulum by the semiclassical method and by the numerical Numerov’s algorithm are compared.

Flexible and stretchable optoelectronics have attracted attention in recent years due to their remarkable capabilities for use in wearable computers, personal monitors, and other systems. These devices can be attached to human skin or fabrics due to mechanical compliance, which is extremely suitable for biomedical or clinical applications, such as bionic devices, monitors, or curing diseases. Recent advanced studies on flexible and stretchable electronic devices and optoelectronics have made possible a variety of soft and performant electronic devices. The paper is focused on the stretchable battery that has great potential to power stretchable light-emitting diode (LED) arrays and other sensors attached on the human body, such as temperature sensors or wearable electrocardiography systems. The stretchable, microfabricated nanogenerator could be attached on the skin or fabrics and will produce energy based on the movements of the human body. The device was fabricated on a polymeric, elastomeric, poly(dimethylsiloxane) (PDMS) sheet. It consists of a piezoelectric thin film of ZnO sandwiched between two stretchable gold electrodes. An innovative technique was used for the deposition of ZnO thin film on the gold electrode-coated polymeric substrate at low temperatures below 150 °C. This is the first attempt to use a uniform film of ZnO, for energy harvesting. We demonstrated that under a strain of 8% the voltage output from this power generator was equal to 2 V and the power output was equal to 160 μW.

The demand for high-speed, high-accuracy optical scanners has already pushed Galvanometer Scanner (GS) and Polygon Mirror (PM) scanners' development limits. Both GS and PM families suffer from a change of the optical path length, change in the incidence angle to the work surface, and change in beam diameter at the work area. Additionally, the PM not only introduces much worse nonlinearity in positioning and speed than the GS, but also produces an asymmetric scan around the optical axis. In practice, the PM is also more challenging to implement, as its physical structure introduces production and tolerance errors such as balance, jitter, speed stability, and perpendicularity. The Øgon, Lens Free Optical Scanner (LFOS), (patented by Tecnica, Inc., New York, New York USA) on the other hand, provides a simple scanning method, linear transfer functions, fixed optical path length, incident beam always normal to the work surface, and a constant beam diameter. This paper describes the optics of the Øgon and compares it with the GS and PM. The analysis shows the Øgon delivering a linear transfer function, where the surface speed, surface beam location, and beam diameter are constant at all times, while the PM and GS fail to keep any of these values stable. More importantly, the Øgon optical performance is defined within the optics and linearly mapped onto the surface by having the light source optical axis, the optical axis of the first reflector, its rotational axis, and the curve path on the work surface rotational axis on the same line. This property alone ensures that the Øgon requires minimal alignment, thus enabling an easy implementation with no calibration. Applications of this novel scanning system are provided to validate the theory and to conclude the study.

This paper will start by mentioning some of the most advanced reflective optics for telescopes, weighting them against those of advanced EUV lithography, and going on to advocate for a reliability approach (trust) bridging technology (including EUV lithography) and system design for advanced CMOS silicon technology (dust). Focusing on the (un)reliability of nanometer transistors, the fact that chips fabricated in 5nm CMOS silicon technology require EUV tools which use holistic lithographic approaches is indirectly making the case for the potential of a much closer integration of circuit design with technology (currently only mildly connected), under a holistic design umbrella.

The paper is focused on the behavioral simulation of the lenses, defined by geometric characteristics (radius, thickness and diameter) and material characteristics, for a certain incident wavelength. The simulation provides a representative layout of the raytracing for refraction and for the second and third reflection on lens surfaces. At the same time, the user can display the rays distribution on a normal plane related to optical axis direction. The authors designed the simulation program and a graphic user interface as a tool to evaluate the parasite images caused by multiple reflections in the specter available for chosen material. Thus, the image disparity for a certain parameter will influence the transmittance through lenses for some radiation or specter. The simulation program is designed to be used in optics, optometry, to analyze the behavior of refractive components and can predict the useful diameter of lenses, diaphragms or aperture stop. The program is also useful, for example, for anyone interested to see how lenses work if the internal reflection of the light on the lens surfaces is considered. The idea of the program comes from the fact that with other ray tracing software and their toolboxes, the multiple reflections are not obvious. The developed simulation program and interface can highlight the ray distribution in an image plane as being suggestive for the ghost images presence and of lens aberrations. Also, there can be easily predicted some geometrical placements in the optical layout, the dimensions of the main apertures and the position of the second order images due to multiple reflection and refraction.

This study utilizes the graphical method we have introduced [V.-F. Duma, A. Schitea, Proc. of the Romanian Acad. Series A 19, 53-60, 2018] and developed [V.-F. Duma, A-L. Dimb, Applied Sciences 11, 8451, 2021] to obtain exact scan patterns of the different configurations of laser scanners with Risley prisms. This method is easier to apply than rather complicated analytical approaches. It is also exact, in contrast to approximate, first order approaches. Simulations are carried out using only simple prisms equations and a mechanical design program, in this case CATIA V5R20 (Dassault Systèmes, Paris, France). Examples of obtained scan patterns are presented and analyzed, continuing previous studies we have performed on this topic and with other prisms parameters, including prisms angles, distance between the prisms and from scanner to target, as well as the rotational speeds of the two prisms. Marshall’s elegant parameters are also considered: M, the ratio of the rotational speeds; k, the ratio of the angles of the prisms. An experimental part validates the simulation results, and an error analysis is performed, to assess the validation of simulation through experiments, but also to evaluate the precision in aligning and positioning the components of the optomechanical setup.

Laser scanners with Risley prisms are one of the most utilized 2D scanning systems. We have introduced a novel, graphical, easy-to-use method to generate exact scan patterns of such devices [V.-F. Duma, A. Schitea, Proc. of the Romanian Acad. Series A 19, 53-60, 2018]. This method was further on developed to study all the four possible configurations of such scanners and to deduce the angular and linear deviations they produce [V.-F. Duma, A-L.Dimb, Applied Sciences 11, 8451, 2021]. In the present study we investigate the way secondary scan patterns can be generated by a pair of rotational Risley prisms. While the issue of total reflections inside the prisms (and how to avoid them) has been approached, this is the first time to our knowledge that patterns using secondary reflections on the facets of the prisms are explored. Equations to obtain the scan patterns are discussed, as well as some of their characteristics.

Histopathology, while suffering from morbidity, cost and time associated with biopsy, plays a key role in detection and monitoring of disease. Optical technologies, with the capability to non-invasively image the cellular structures in real time, have the potential to revolutionize medicine. Gabor-domain optical coherence microscopy (GDOCM) is a noninvasive, high-definition, three-dimensional imaging technique leveraging concepts of low-coherence interferometry, liquid lens technology, confocal microscopy, high-speed imaging, and precision scanning. By operating at a high numerical aperture to improve transverse resolution and recovering the resulting loss in depth of focus by acquiring multiple volumes dynamically refocusing inside the sample with no moving parts, GDOCM breaks the cellular resolution limit of optical coherence tomography (OCT) and achieves isotropic 2 μm resolution in 3D. GDOCM enables optical biopsy capabilities that span both medical and industrial applications. In the past decade, GDOCM has been demonstrated for cellular imaging in 3D in a number of clinical applications, including dermatology, oncology and ophthalmology, as well as to characterize materials in industrial applications. The structural imaging capability of GDOCM has been enhanced by adding functional modalities and by incorporating machine learning techniques. In particular, convolutional neural networks were applied to automatically segment the endothelial cells in human cornea for quantitative, unbiased assessment of corneal health. A novel algorithm for optical coherence tomography angiography (OCTA), an attractive diagnostic tool for non-invasive, label-free vascular imaging in vivo, was demonstrated in conjunction with GDOCM to extract high-resolution cutaneous vasculature, significantly improving the visualization and characterization of micro-capillaries in vivo.

The astronomers and the general population are fascinated with the exoplanet detection. More than 4,000 planets in various stages of planetary evolution have been reported so far. By far the largest number of those are the so-called Super-Earths, relatively cold planets orbiting a large, red giant star, with diameters up to 1 AU, most of them at about one hundred light-year distance from us. For infrared spectral regions, the planet-to-star S/N ratio is about to 10⁻⁵. Interferometric techniques are often implemented to improve the detectability of a faint object. We proposed a rotational shearing interferometer (RSI) for exo-planet detection. We describe the status of this projects. The basic concept has been demonstrated in the laboratory. We are now expanding the detection capabilities of the RSI when the interferometer is not precisely aligned on the star. We analyze the extreme case of a Super Earth.

In the case of the adhesive fixations of the fully ceramic veneers, the light-curing diacrylic cement can be contracted towards the light source during its polymerizations. The scope of this work is to observe the differences in veneers adhesion, as well as the difference of all structures (i.e., dental surface, cement, and internal surface of the veneers) depending by the photopolymerization direction. The study is performed in vitro on five extracted teeth and held in formalin 10%. Each tooth is split in two, in the oral-vestibule direction. On each tooth section, a lithium disilicat veneer is fixed. Half of the tooth is photopolymerized during veneer fixing, perpendicular from the veneer direction, and the other half of the same tooth is photopolymerized from the direction of the tooth, by its structure. Using OCT, in both cases, the space between the tooth and the veneer is measured, and the difference of structure in the mass of the cement is followed. Due to the contraction towards the light source, there are significant differences in the structure of the cement mass, its particles being more concentrated in the direction of light-curing. The results are interpreted based on the perfomed OCT analysis. The adhesion of a veneer is better if the photopolymerization is made from the direction of the tooth, through its structure, practically pulling the cement particles, by its contraction towards the dental structure.

Aesthetic dentistry is in high demand today due to the various prosthetic options that enhance patients’ smile design and self-esteem, consequently. The aim of our in vitro studies was to assess the effect of our patented, crenelated veneers design compared to conventional ones on their marginal and internal gap to the prepared tooth surface [Măroiu, A.C., Sinescu, C., Duma, et al., Medicina 57, 772 (2021)]. Twenty-four lithium disilicate ceramic veneers were obtained using CAD/CAM technology. The samples were divided into two groups: twelve veneers with a linear marginal contour - conventional (CO), and twelve veneers with the novel sinusoidal marginal design - crenelated (CR). All veneers were subsequetly luted to the dental surface by using a specific dental cement. The marginal gaps along the adhesive interfaces were analyzed using optical microscopy. Micro-Computed Tomography (CT) was used to investigate both the internal fit of the veneers and the homogeneity of the luting cement. Significant differences between CO and CR veneers were determined by using STATA and one-way ANOVA tests: (i) the marginal gap was larger for CO than for CR veneers; (ii) the internal adaptation was better for CR veneers; (iii) the porosity mean within the cement was not significantly different for CO and CR veneers, with a smaller standard deviation for the CR group. The internal gaps were modelled using the micro-CT results. Characteristic functions were obtained to compare volumes of luting cement for these two veneers. The novel veneers’ design triggered better marginal and internal fit of the restorations to the prepared dental surface.

Advances in digital technologies create the opportunity for much more predictable and safe dentistry. From the examination of the patient to the final treatment plan, digital technologies can provide a much comprehensive visualization and understanding. A key aspect for any long-lasting prosthetic restoration is the accuracy of the impression, which generates a working model (digital or conventional). The precision of digital impressions is essential to obtain high-quality restorations, as well as to obtain the predictability of the treatment. There are some challenging factors that can influence the precision of direct digital impressions, that’s why the clinician must be aware and find methods to counteract them. The main advantages of intraoral scanners are the possibility to completely replace the conventional impression, reducing the discomfort for the patient, and the overall costs of the impression materials. Switching from digital to conventional in impression technique increase the predictability, the precision, and the efficiency. From the clinician point of view, the overall working time and the effort of the dentist can be reduced, in order to obtain the most appropriate treatment outcome for every patient.

An important challenge in today’s dentistry is to create sturdy and aesthetic restorations. Dental research aims to create restorations with long-term durability and optical properties similar to healthy natural teeth. Recent works have shown that the magnetic handling of a dental adhesive doped with magnetic nanoparticles (MNPs) improves the adhesion between the composite and the dentin. This study presents the preparation of dental adhesives loaded with iron oxide (Fe₃O₄) NPs incorporated in SiO₂ shells, and their applications in the creation of dental veneers. Extracted incisors were prepared for veneering and divided in two groups: Group A was bonded with normal adhesive and Group B was bonded with the augmented adhesive, in the presence of a permanent magnet. The samples were analyzed using stereomicroscopy, optical coherence tomography (OCT), and scanning electron microscopy (SEM), the latter combined with energy dispersive analysis of X-rays (EDAX). All techniques enabled the visualization of the veneer-adhesive and adhesive-dentin interfaces: (i) stereomicroscopy demonstrated that the adhesive layer was thinner for Group B and revealed conglomerates of MNPs in the adhesive layer; (ii) OCT enabled a visualization of the marginal closure, as well as of defects in the two interfaces; (iii) SEM provided a high-resolution image of the adhesive layer, whereas EDAX furnished an elemental analysis of the augmented adhesive. In conclusion, under the action of an external magnetic field, MNPs can penetrate deeper into the demineralized structure of the tooth, reducing the thickness of the adhesive layer and, thereby, decreasing the probability of microleakage.

Risley prisms systems consist of two-wedge aligned prisms that deviate a light beam or wavefront. The relative angle between prisms determines the displacement of the central point wavefront. In the case of wavefront propagation through the Risley system, the relative angle also can introduce a controlled tilt. Then, the beam’s or wavefront displacement direction is controlled by changing the relative angle between prisms. Risley prisms have been used in multiple applications such as super-resolution imaging and field of view (FOV) extension, steering systems, precision pointers, scanning systems, and wavefront alignment and positioning. This paper presents a description of the techniques used by Risley prisms making a compilation of their most essential characteristics. One of the related applications is reviewed on a Vectorial Shearing Interferometer. The paper overviews the advantages and disadvantages of using Risley prisms in different valuable applications.

The stabilization of portable laser systems is of major importance for improving performance and ensuring high mobility of devices. These systems can be grouped into two classes: resonant and non-resonant, each requiring different approaches. The article presents the conceptual and physical results of research, focused on the industrial application of a stabilization solution in the field of portable laser equipment used in the medical field. The proposed solutions to the major problems encountered are presented: mobile system motion detection and correction signal extraction, mechatronic positioning system design, feedback loop design, concept of a system performance certification stand. Aspects regarding the optimal actuation solution are discussed, comparing the piezoelectric, electrodynamic and electromagnetic ones. These are analyzed for gauge conditions imposed in terms of accuracy, range, thermal stability, the presence and size of nonlinearities and hysteresis. A major problem in these portable systems is their miniaturization. A scanning solution is presented based on the use of LIGA-Laser technology for mechanical microstructures and micromagnets, in bulk or 2D array structure manufacturing, which interact with planar coils. The solution has a practically proven improvement, not used so far in scanners, respectively a structure with two coupled degrees of freedom for each direction of movement, on the principle of dynamic absorber. The preliminary results for the numerical signal processing and the mechatronic construction of the dynamic positioning system of the entire laser assembly are also presented, as a possible option for the use of small size sources, having the advantage of an easy autofocus.

The paper presents an optical method of damping vibration present in manually operated laser surgical devices. Considering the frequency range of the physiological tremor of 5-15Hz, the design of two compliant positioning mechanisms on 2 axes was made, which will have the role of supporting and moving the focusing lens of the laser device. A couple of compliant structures were subjected to static and dynamic finite element analyzes (modal analysis) to determine the displacement-force characteristic and resonant frequencies, eliminating the risk of operating in the frequency band of physiological tremor. Finally, the structures were teste in laboratory for final experimental results.

This paper presents a review of the activities on optical coherence tomography (OCT) in the Applied Optics Group (AOG), University of Kent, encompassing optical devices, sources for OCT as well as OCT applications. Out of the directions of applications approached, two fields are selected, applications in medical imaging with emphasis on ophthalmology and endoscopy and in non destructive testing. An important advantage of OCT is that high axial resolution is achievable at comfortable working distances, which is an important requirement for safe scanning of patients as well as of valuable materials or objects of art.

As tremor is a condition which occurs in all individuals, its effects can have a big impact on person’s everyday life. If we are considering professionals who rely on manual labor to perform precise activities, tremor becomes the source of many problems. Moreover, as specific literature highlights, tremor occurs mostly at hands and fingers level. The aim of this paper is to provide an enhanced controller for a precision positioning system used in laser medical instruments. The controller shall be tuned in such way to overcome the constraints imposed by electromagnetic actuators, yet providing high precision positioning, considering the application requirements (approximatively 50 µm maximum displacement).

In this work a review of the research performed on laser ignition (LI) in internal combustion engines, especially of gasoline engines, will be presented. The path from the first demonstration of LI in an internal combustion engine to the first operation by LI of a 4-cylinder gasoline test engine and to the implementation of LI in a real automobile will be discussed. Steps taken toward developing a spark-plug-like LI system for automobile, stationary gas engines for energy cogeneration or for space applications will be described. Results on multi-point LI of methane-air mixtures in a static, constant-volume combustion chamber will be introduced, proving that multi-point LI can extend the limits of flammability. It is concluded that LI has reached a quite high degree of technical maturity and that the advantages of using LI technique versus ignition by an electrical spark plug were demonstrated.

The paper presents a solution for inspection of contact lens based on machine vision. Being characterized by a high degree of automation the proposed system satisfies the current manufacturing requirements that require short times to obtain the final product. The machine vision system(MVS) proposed integrates two classic systems used in the inspection process: a profile projector and a system for image acquisition and processing. For validating the results, three contact lenses from the same batch were inspected generating the possibility to identify possible defects or technological errors from manufacturing process. Evaluated parameters were the lens diameter(LD), front optical radius(FOR) and the front peripheral radius(FPR) of the lens. The study presents a series of important conclusions about the possibility of integrating vision systems(VS) in the contact lens inspection process, as well as the performance of the proposed system.

Nowadays the use of lasers in medicine is becoming more and more popular. To improve the quality of operations, attempts by various researchers are being made to use lasers in cooperation with robotic systems. Fiber lasers have a high potential for combining due to the fact that the fiber is quit flexible and allows to deliver laser emission to the operated tissues without significant losses. To fulfil the potential of using lasers in cooperation with robots, it is necessary to evaluate the data of the reflected optical signal. In this research the dependence of an optical reflected signal from the distance to different surfaces was evaluated. Experiments were conducted on motorized setting bench Tesa TPS 500 with wavelength 470 nm of a diode fiber laser and the range of power from 0.1 W to 1.6 W. Different materials were chosen for their reflective and mechanical properties: metal surface, plexiglas, and flexible composition based on (C₁₂H₁₈O₉)_n. The experiments showed that the dependence of the sensor data on the distance to the surface has a nonlinear form, which can be divided into three characteristic areas. The first one, from 0 to 0.2 mm, carries tip contact with the surface information and has no clearly expressed dependence. The second one, situated at the distance from the surface from 0.2 to 1 mm, has well approximated dependence. The third one, when the distance is more than 1mm from the surface, obeys the law of inverse squares. The results obtained can be used to improve robotic laser contact or noncontact cutting of soft tissues.

Robust, non-destructive testing imaging instruments, capable to provide valuable information from within the body of materials is important for both quality control and the development of new materials, for industrial and medical applications. Conventional non-destructive testing (NDT) methods, such as radiographic or ultrasound-based techniques, allow for deep axial range imaging, however, they are either using non-safe radiation or/and exhibit low imaging resolutions. The speed at which the standard NDT methods deliver images is also limited. The development of photoacoustic (PA) and optical coherence tomography (OCT) applications in the field of NDT have grown exponentially over the past years, offering faster, higher resolution images. Both techniques, PA and OCT bring a plethora of benefits to the current methods. However, a multitude of challenges still needs to be addressed to truly make either of them the technique of choice for NDT applications. In this manuscript, a short overview of the challenges that these two imaging techniques are facing when used for NDT applications is presented. Illustrative high-resolution images, produced by a dual PA/OCT imaging instrument developed within the Applied Optics Group at the University of Kent are presented. These images demonstrate unique capabilities for NDT applications.