Digital Laser Research Articles

Numerical model characterization of the sound transmission mechanism in the tympanic membrane from a high-speed digital holographic experiment in transient regime.

A methodology for the development of a finite element numerical model of the tympanic membrane (TM) based on experiments carried out in the time domain on a cadaveric human temporal bone is presented. Using a high-speed digital holographic (HDH) system, acoustically-induced transient displacements of the TM surface are obtained. The procedure is capable to generate and validate the finite element model of the TM by numerical and experimental data correlation. Reverse engineering approach is used to identify key material parameters that define the mechanical response of the TM. Finally, modal numerical simulations of the specimen are performed. Results show the feasibility of the methodology to obtain an accurate model of a specific specimen and to help interpret its behaviour with additional numerical simulations. STATEMENT OF SIGNIFICANCE: Improving knowledge of the dynamic behavior of the tympanic membrane is key to understanding the sound transmission system in human hearing and advance in the treatment of its pathologies. Recently we acquired a new tool to carry out experiments in transient regime by means of digital laser holography, capable of providing a large amount of information in a controlled transient test. In this work, these data are used to develop a methodology that generates a numerical model of the tympanic membrane based on numerical-experimental correlations. It is important to be able to develop models that fit specific patients. In this work, additional modal simulations are also presented that, in addition to validating the results, provide more information on the specimen.

Far field energy distribution control using a coherent beam combining femtosecond digital laser.

We report on far field energy distribution control using a coherent beam combining femtosecond digital laser employing 61 tiled channels. Each channel is considered as an individual pixel where amplitude and phase are controlled independently. Applying a phase difference between neighboring fibers or neighboring fiber-lines gives high agility for far field energy distribution and paves the way for deeper exploration of phase patterns as a tool to further improve tiled-aperture CBC laser efficiency and far field shaping on demand.

Nanosecond compressive fluorescence lifetime microscopy imaging via the RATS method with a direct reconstruction of lifetime maps.

The RAndom Temporal Signals (RATS) method has proven to be a useful and versatile method for measuring photoluminescence (PL) dynamics and fluorescence lifetime imaging (FLIM). Here, we present two fundamental development steps in the method. First, we demonstrate that by using random digital laser modulation in RATS, it is possible to implement the measurement of PL dynamics with temporal resolution in units of nanoseconds. Secondly, we propose an alternative approach to evaluating FLIM measurements based on a single-pixel camera experiment. In contrast to the standard evaluation, which requires a lengthy iterative reconstruction of PL maps for each timepoint, here we use a limited set of predetermined PL lifetimes and calculate the amplitude maps corresponding to each lifetime. The alternative approach significantly saves post-processing time and, in addition, in a system with noise present, it shows better stability in terms of the accuracy of the FLIM spectrogram. Besides simulations that confirmed the functionality of the extension, we implemented the new advancements into a microscope optical setup for mapping PL dynamics on the micrometer scale. The presented principles were also verified experimentally by mapping a LuAG:Ce crystal surface.

Influence of open joints on blasting damage and crack propagation of PMMA

In order to study the influence of open joint on blasting damage and crack propagation, plexiglass (PMMA) specimens with open joints were designed to carry out a study using a digital laser dynamic caustic experimental system. The results showed that the crack could not pass through the opening joint. The joint could promote the destruction of the medium between the borehole and the joint. Affected by the reflected stress wave at the joint, the crack was no longer simply subjected to tensile stress. Instead, it was influenced by the combined action of tensile stress and shear stress. The fracture type of crack changed from Type I to mixed Types I and II. During the reflected stress wave stage, the crack growth rate and intensity factor of dynamic stress increased.

HIBISCUS: Simulator for the development of control strategies for coherent beam combining lasers with PISTIL technique

CBC (Coherent Beam Combining) is a key technology for the realisation of intense lasers. In this context, PISTIL (PISton and TILt interferometry), a precise metrology tool for measuring segmented wave surfaces, has been developed and used in particular to characterise and diagnose CBC ultrafast and digital laser in the framework of the XCAN (X Coherent Amplification Network) project at the École Polytechnique. We propose here to use it in a way to help the optimisation of control techniques by including PISTIL in an XCAN type CBC laser simulator. This will allow an easy tuning of the control laws, outside the clean rooms in which these large lasers are deployed and without the need to start them up.

Chapter 7: Technological Aids and Coronal Caries.

In recent decades, dentistry has developed significantly in all areas. While in the past, caries was mainly treated operatively, the today's management has shifted toward noninvasive, minimal invasive, and, only if needed, invasive treatment options. Aiming at enabling the most noninvasive or conservative treatment option requires early caries detection, which, however, remains challenging. The progression of early or noncavitated caries lesions can nowadays be successfully controlled, as well as lesions arrested by oral hygiene procedures combined with the use of fluorides, sealants, or resin infiltration. Methods such as near-infrared light transillumination, fibre-optic transillumination, digital fibre-optic transillumination, laser fluorescence, or quantitative light fluorescence measurements were introduced in the dental market to provide X-ray-free caries detection, assessment, and monitoring. For approximal surfaces that are not directly visible, bitewing radiography is still the standard in detecting caries lesions. The use of artificial intelligence has become the most recent technological aid for the detection of caries lesions on bitewing radiographs and clinical images and has to be understood as an emerging technology, which requires extensive research in the future. The aim of this chapter is to give an overview of different possibilities to detect coronal caries lesions and suggestions of how to improve this process.

Evaluation of trueness and precision of removable partial denture metal frameworks manufactured with digital technology and different materials.

The aim of this study is to evaluate the accuracy of removable partial denture (RPD) frameworks produced using different digital protocols. 80 frameworks for RPDs were produced using CAD-CAM technology and divided into four groups of twenty (n = 20): Group 1, Titanium frameworks manufactured by digital metal laser sintering (DMLS); Group 2, Co-Cr frameworks manufactured by DMLS; Group 3, Polyamide PA12 castable resin manufactured by multi-jet fusion (MJF); and Group 4, Metal (Co-Cr) casting by using lost-wax technique. After the digital acquisition, eight specific areas were selected in order to measure the Δ-error value at the intaglio surface of RPD. The minimum value required for point sampling density (0.4 mm) was derived from the sensitivity analysis. The obtained Δ-error mean value was used for comparisons: 1. between different manufacturing processes; 2. between different manufacturing techniques in the same area of interest (AOI); and 3. between different AOI of the same group. The Δ-error mean value of each group ranged between -0.002 (Ti) and 0.041 (Co-Cr) mm. The Pearson's Chi-squared test revealed significant differences considering all groups paired two by two, except for group 3 and 4. The multiple comparison test documented a significant difference for each AOI among group 1, 3, and 4. The multiple comparison test showed significant differences among almost all different AOIs of each group. All Δ-mean error values of all digital protocols for manufacturing RPD frameworks optimally fit within the clinical tolerance limit of trueness and precision.

3D-Printing of succulent plant-like scaffolds with beneficial cell microenvironments for bone regeneration.

Biomimetic materials with complicated structures inspired by natural plants play a critical role in tissue engineering. The succulent plants, with complicated morphologies, show tenacious vitality in extreme conditions due to the physiological functions endowed by their unique anatomical structures. Herein, inspired by the macroscopic structure of succulent plants, succulent plant-like bioceramic scaffolds were fabricated via digital laser processing 3D printing of MgSiO3. Compared with conventional scaffolds with interlaced columns, the structures could prevent cells from leaking from the scaffolds and enhance cell adhesion. The scaffold morphology could be well regulated by changing leaf sizes, shapes, and interlacing methods. The succulent plant-like scaffolds show excellent properties for cell loading as well as cell distribution, promoting cellular interplay, and further enhancing the osteogenic differentiation of bone marrow stem cells. The in vivo study further illustrated that the succulent plant-like scaffolds could accelerate bone regeneration by inducing the formation of new bone tissues. The study suggests that the obtained succulent plant-like scaffold featuring the plant macroscopic structure is a promising biomaterial for regulating cell distribution, enhancing cellular interactions, and further improving bone regeneration.

Digitizing an Excavation: A Laser Scanning Database of Maya Architectural Remains

Excavating an ancient Maya city requires a long-term archaeological project that entails adequate documentation procedures for the unearthed remains, frequently of monumental scale and with difficult preservation conditions. A digital laser scanner survey methodology was designed and implemented to document the exposed architecture and to follow-up the archaeological excavation of the Maya site of La Blanca (Peten, Guatemala). All scans collected during the different field seasons were stored and aligned in a common reference system. Thus, an accurate digital three-dimensional database was obtained, including all the architectural remains found, some of which had to be reburied to ensure their preservation. The resulting database is a helpful repository that facilitates to extract all the graphic outputs required for: planning the next excavation campaigns, monitoring the preservation of the buildings, studying the architecture and construction technology in detail, and disseminating the excavation results. This paper describes the methodology and procedures used to build-up this database.

From direct to digital survey. The Abbey of San Giovanni Battista in Lucoli (L’Aquila)

Lucoli is a scattered municipality in the area of L’Aquila, in the Italian region of Abruzzo. In this place between the mountains of the conca Aquilana stands the Abbey of San Giovanni Battista, an important historic and religious site. Despite the damage suffered caused during the 2009 earthquake, the local people still use it and look at it as a symbol of community. With the aim of analyse and so mitigate the seismic vulnerability, the abbey has been the subject of an architectural survey with direct method in a first step, and then of digital laser scanning survey at a later stage, to integrate and verify the first.

Effect of picosecond laser cleaning on surface morphology and properties of stainless steel

In order to explore the influence of picosecond laser on the cleaning quality of 316L stainless steel, and verify the feasibility of laser cleaning technology on stainless steel. In this paper, we used a picosecond laser for cleaning experiments on contaminated 316L stainless steel to study the effect of different laser process parameters on its surface cleaning quality and used a scanning electron microscope, energy dispersive X-ray spectrometer, digital microhardness tester and laser confocal microscope and other testing techniques to test the samples before and after cleaning. The results show that picosecond laser removal of stainless steel surface contaminants was the most effective when the laser power density was 19.1 × 105 W/cm2, the repetition rate was 80 kHz, the scanning speed was 1900 mm/s and the scanning spacing was 0.03 mm. Compared with the traditional cleaning process, the surface quality of the laser-cleaned samples was higher and more effective, which provided a reference from the application of laser cleaning technology on stainless steel surfaces.

Digitally Printed Liquid Metal Composite Antenna for Energy Harvesting: Toward Energy‐Autonomous Battery‐Free Wearable Bioelectronics

AbstractRapid progress on wearable bioelectronics holds the promise for remote patient monitoring. However, there are concerns related with the use of batteries, including the need for frequent charging, user safety, and environmental pollution. The development of rapidly deployable battery‐free patches that harvest their energy from external sources is highly desired. Here, untethered battery‐free patches through far‐field energy harvesting are demonstrated. Taking advantage of a stretchable biphasic liquid metal‐based ink and digital fabrication techniques, that is, direct printing, and laser patterning, tailor‐made customized antennas are fabricated over various substrates, including polydimethylsiloxane, Kapton, and wound‐dressing medical‐grade adhesives. Folded dipole and planar inverted‐F antennas (PIFA) are evaluated and they are optimized for an over‐the‐body scenario. Compared to previous works that only show communication of data at <1 Hz, here, battery‐free acquisition and transmission of electrocardiogram (ECG) data at 100 Hz via Bluetooth is demonstrated. It is shown that using 3 parallel PIFA antennas, it is possible to harvest ≈10 mW at 30 cm from the transmitter, which is ≈7× the required power by the ECG circuit. This study proves the feasibility of next generation of battery‐free wearable biomonitoring patches/e‐textiles and demonstrates materials and methods for fabrication of optimized printed antennas.

New digital confocal laser microscopy may boost real-time evaluation of endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) from solid pancreatic lesions: Data from an international multicenter study

Pancreatic cancer is an aggressive malignancy and a leading cause of cancer death worldwide; its lethality is partly linked to the difficulty of early diagnosis. Modern devices for endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) were recently developed to improve targeting and sampling of small lesions, but innovative technologies for microscopic assessment are still lacking. Exvivo fluorescence confocal laser microscopy (FCM) is a new digital tool for real-time microscopic assessment of fresh unfixed biological specimens, avoiding conventional histological slide preparation and potentially being highly appealing for EUS-FNB specimens. This study evaluated the possible role of FCM for immediate evaluation of pancreatic specimens from EUS-FNB. It involved comparison of the interobserver agreement between the new method and standard histological analysis during international multicenter sharing of digital images. Digital images from 25 cases of EUS-FNB obtained with real-time FCM technology and 25 paired digital whole-slide images from permanent conventional paraffin sections were observed by 10 pathologists from different Institutions in Europe, Japan, and the United States, in a blinded manner. The study evaluated 500 observations regarding adequacy, morphological clues, diagnostic categories, and final diagnosis. Statistical analysis showed substantial equivalence in the interobserver agreement among pathologists using the two techniques. There was also good inter-test agreement in determining sample adequacy and when assigning a diagnostic category. Among morphological features, nuclear enlargement was the most reproducible clue, with very good inter-test agreement. Findings in this study are from international multicenter digital sharing and are published here for the first time. Considering the advantages of FCM digital diagnostics in terms of reduced time and unaltered sample maintenance, the exvivo confocal laser microscopy may effectively improve traditional EUS-FNB diagnostics, with significant implications for planning modern diagnostic workflow for pancreatic tumors. This study was not supported by any funding source.

Laser Additive Remanufacturing Cladding Thickness Detection System

As an important parameter in laser additive remanufacturing technology, cladding thickness is related to the quality of remanufacturing. Thickness detection during the cladding process can help improve the cladding quality and facilitate manual adjustment of parameters in real time to optimize the cladding thickness. This system develops a set of cladding thickness detection system based on laser displacement sensor. The system consists of hardware and software parts. The hardware part includes laser displacement sensor, mounting plate, digital signal acquisition device and laser cladding system. The software part a set of data acquisition software is developed according to Visual Studio. The system uses two methods to measure, and eliminates the error caused by the tilt factor of the worktable, and realizes the online measurement of cladding thickness.

AR/VR light engines: perspectives and challenges

Augmented reality (AR) and virtual reality (VR) have the potential to revolutionize the interface between our physical and digital worlds. Recent advances in digital processing, data transmission, optics, and display technologies offer new opportunities for ubiquitous AR/VR applications. The foundation of this revolution is based on AR/VR display systems with high image fidelity, compact formfactor, and high optical efficiency. In this review paper, we start by analyzing the human vision system and the architectures of AR/VR display systems and then manifest the main requirements for the light engines. Next, the working principles of six display light engines, namely transmissive liquid crystal display, reflective liquid-crystal-on-silicon microdisplay, digital light processing microdisplay, micro light-emitting-diode microdisplay, organic light-emitting-diode microdisplay, and laser beam scanning displays, are introduced. According to the characteristics of these light engines, the perspectives and challenges of each display technology are analyzed through five performance metrics, namely resolution density, response time, efficiency/brightness/lifetime, dynamic range, and compactness. Finally, potential solutions to overcoming these challenges are discussed.

Improved numerical method for determination of pavement mean texture depth from 3-dimensional digital image

The conventional manual sand-patch method of mean texture depth (MTD) measurement is unsuitable for network level pavement condition monitoring. Relying on 2-D mean linear profile depth (MPD) to estimate 3-D MTD is also unsuitable because MTD-MPD regression relationship varies from one pavement mix type to another. This problem of network level MTD measurements and monitoring can be overcome if MTD could be numerically determined from 3-D digital laser images. All the numerical MTD determination methods proposed by researchers in recent years made a common invalid assumption that the MTD top surface was defined by the high texture peaks of the test surface. This study presents evidence to show that the top surface defining MTD actually lies below the highest peaks of the test surface. Next, applying the concept of planation surface, a novel numerical procedure is proposed to identify a reference surface for MTD calculation by means of a second-derivative plot of peak-height percentiles. The validity of the proposed method was verified experimentally with measured MTD values of both laboratory fabricated specimens and in-service pavements. For four different surface course materials, the errors in the predicted MTD values range from 0.20 to 7.31 %. The proposed method produced improved accuracy in MTD predictions compared with the existing methods which were based on incorrectly assumed MTD top surfaces.

3D digital dental models’ accuracy for anthropological study: Comparing close-range photogrammetry to μ-CT scanning

X-rays micro-Computed Tomography (X-μCT) is a non-invasive and non-destructive technique primarily used for the 3D reconstruction of internal/external object structures. Despite the great potential, X-ray exposure for samples of archaeo-anthropological interest can compromise the integrity of the finds, altering the results for future investigations. The aim of this study is to evaluate whether close-range photogrammetry is a viable alternative in terms of non-invasiveness, low cost, efficiency and precision to the 3D external surface models with respect to X-μCT scanning. Photogrammetry was applied to small and highly diagenized archaeological human teeth characterized by irregular and fragmented surfaces. The accuracy of the 3D model and the metric information obtained from photogrammetry was evaluated comparing the micro-measurements obtained by digital caliper and Confocal laser scanning microscope (CLMS). The results obtained show the effectiveness of close-range photogrammetry to create a 3D model with metric information as accurate as those from micro-CT, with the advantage of reproducing textural information.

Self-loading microfluidic platform with ultra-thin nanoporous membrane for organ-on-chip by wafer-level processing

Embedded porous membranes are a key element of various organ-on-chip systems. The widely used commercial polymer membranes impose limits with regard to chip integration and thinness. We report a microfluidic chip platform with the key element of a monolithically integrated, ultra-thin (700 nm) nanoporous membrane made of ultra-low-stress (<35 MPa) SixNy for culturing and testing reconstructed tissue. The membrane is designed to support various in vitro tissues including co-cultures and to allow passage of molecules but not of cells. A digital laser write method was used to produce nanopores with deterministic but highly flexible positioning within the membrane. A thin layer of photoresist was exposed by accumulation of femtosecond pulses for local two-photon polymerization, which allowed nanopores as small as 350 nm in diameter to be generated through the membranes in a subsequent plasma etch process. The fabricated membranes were used to separate a microfluidic chip into two compartments, which are connected to the outside by microchannel structures. With unique side inlets for fluids, all cells are exposed to identical flow velocities and shear stresses. With the hydrophilic nature of chip materials the self-loading seeding is controlled bottom-up by capillary forces, which makes the seeding procedure homogeneous and less dependent on the operator. The chip is designed to allow fabrication by wafer-level MEMS manufacturing technologies without critical assembly steps, thereby promoting reproducibility and scale-up of fabrication. In order to establish a fully functional test system to be used in a lab incubator, a holder for the bare chip was designed and 3D-printed with additional elements for gravity driven pumping. In order to mimic physiological conditions, the holder was designed to provide not only media delivery but also appropriate shear stress to the tissue. To prove usability, murine microvascular endothelial cells (muMEC) were seeded on the membrane within the chip. Cell compatibility was confirmed after 3 days of dynamic cultivation using fluorescence live/dead assays. Cultivation proved to be reproducible and led to confluent layers with cells preferentially grown on nanoporous areas. The system can in future be cost effectively manufactured in larger quantities in MEMS foundries and can be used for a wide variety of in vitro tissues and test scenarios including pumpless operation within cell incubator cabinets.

Research on protective mechanism of semicircular arc pre-crack under impact load

In this paper, a plexiglass (PMMA) specimen is designed for dynamic impact testing based on the digital laser dynamic caustics experimental system. The impact of offset distance on dynamic fracture behavior of PMMA specimens with semicircular arc pre-cracks in two different directions is investigated. Research shows that: the pre-crack initiates anew when the horizontal distance between the moving crack and the semicircular arc pre-crack is small. With the increase of horizontal distance, the pre-crack attracts the crack first and then repels it. When the distance reaches a critical threshold, the pre-crack has no considerable effect on the moving crack. The above conclusions are not affected by the direction of the semicircular arc pre-crack. Furthermore, the crack deflection angle and the horizontal offset distance of the two groups of experiments conform to a linear function. When the horizontal offset distance is small, the middle part of the pre-crack initiates again. When the moving crack is outside the arc pre-crack, the medium in the pre-crack is the stress relief zone, according to the numerical data. The ability of the medium to resist impact damage can be effectively boosted by placing acceptable pre-cracks on the medium's periphery.

Function Integration in Additive Manufacturing: Design and Realization of an LPBF Built Compressed Air Motor.

We present a compressed air motor, completely built by laser powder bed fusion. To highlight the fully functional integration by additive manufacturing, the rotor, stator, bearings, turbine, gas inlet and outlet were all built in a single print job. The material used was Inconel 718, and the motor was 44 mm tall and 12 mm in diameter. With the rotation axis of the motor in print in the direction of the laser powder bed fusion process, no build supports are needed, and thus the rotor and stator are fully moveable against each other. Plain bearings were used to position the rotor inseparably inside the stator, with a bearing gap of 0.2 mm, resulting in stable rotation. The idle rotation speed of the motor was measured with a digital laser measuring device as a function of air pressure and inlet size. With linear behavior between the rotation speed and gas pressure of up to 5.5 bar, the motor can be easily controlled. With varying gas inlet sizes, the idle rotation speed of the compressed air motor is also varied. A maximum rotation speed of 90,000 rpm was achieved at 1.5 mm gas inlet size and 3 bar gas pressure.