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Graphene quantum dots (GQDs) are attractive fluorescent nanoparticles that have wide applicability, are inexpensive, nontoxic, photostable, water-dispersible, biocompatible and environmental-friendly. Various strategies for the synthesis of GQDs have been reported. However, simple and efficient methods of producing GQDs with control over the size of the GQDs, and hence their optical properties, are sorely needed. Herein, an ultra-fast and efficient laser writing technique is presented as a means to produce GQDs with homogeneous size from graphene produced by the instantaneous photothermal gasification and recrystallization mechanism. Controlling the laser scan speed and output power, the yield of GQDs can reach to be about 31.458 mg/s, which shows promising potential for large-scale production. The entire process eliminates the need for chemical solvents or any other reagents. Notably, the prepared laser writing produced GQDs (LWP-GQDs) exhibit blue fluorescence under UV irradiation of 365 nm and the Commission Internationale de L’Eclairage (CIE) chromaticity coordinates is measured at (0.1721, 0.123). Overall, this method exhibits superior advantages over the complex procedures and low yields required by other existing methods, and thus has great potential for the commercial applications.

Integration of functional structures onto foldable, stretchable and disposable paper substrates is a growing field in low cost electronics. Herein this paper, we present a laser printing technology to directly convert fibrous paper to molybdenum carbide-graphene composite with exceptional conductivity (

At present the trends in paper and packaging industries are the personalization of products and the use of novel high-tech materials. Laser processes as non-contact and flexible techniques seem to be the obvious choice to address those developments. In this paper we present a basic understanding of the occurring mechanisms of laser based engraving of different paper and paperboard materials, using a picosecond laser source at 1064 nm. The influences on the beam-paper-interaction of grammage, the composition of the paper matrix, as well as the paper inherent cellulose fibers were investigated. Here the ablation threshold of commercially available paper was determined and a matrix ablation effect under the 1064 nm radiation observed. These results were characterized and qualified mainly by means of laser scanning microscope (LSM) micrographs in combination with color-space analytics.

Traditional industry sectors, like paper making industry, tend to stay within well-known technology rather than going forward towards promising, but still quite new technical solutions and applications. This study analyses the feasibility of the laser cutting in large-scale industrial paper making processes. Aim was to reveal development and process related challenges and improvement potential in paper making processes by utilizing laser technology. This study has been carried out, because there still seems to be only few large-scale industrial laser processing applications in paper converting processes worldwide, even in the beginning of 2010's. Because of this, the small-scale use of lasers in paper material manufacturing industry is related to a shortage of well-known and widely available published research articles and published measurement data (e.g. actual achieved cut speeds with high quality cut edges, set-up times and so on). It was concluded that laser cutting has strong potential in industrial applications for paper making industries. This potential includes quality improvements and a competitive advantage for paper machine manufacturers and industry. The innovations have also added potential, when developing new paper products. An example of these kinds of products are ones with printed intelligence, which could be a new business opportunity for the paper industries all around the world.

Paper making and converting industry in Europe is suffering from transfer of basic manufacturing to fast-growing economies, such as China and Brazil. Pulp and paper production volume in Finland, Sweden and France was the same in 2011 as it was in 2000. Meanwhile China has tripled its volume and Brazil doubled. This is a situation where innovative solutions for papermaking and converting industry are needed. Laser can be solution for this, as it is fast, flexible, accurate and reliable. Before industrial application, characteristics of laser beam and paper material interaction has to be understood. When this fundamental knowledge is known, new innovations can be created. Fulfilling the lack of information on interaction phenomena can assist in the way of lasers for wider use of technology in paper making and converting industry. This study was executed by treating dried kraft pulp (grammage 67 g m-2) with different laser power levels, focal point settings and interaction time. Laser equipment was TRUMPF TLF HQ2700 CO2 laser (wavelength 10.6 μm). Interaction between laser beam and dried kraft pulp was detected with multi-monitoring system (MMS), which consisted of spectrometer, pyrometer and active illumination imaging system. There is two different dominating mechanisms in interaction between laser beam and paper material. Furthermore, it was noticed that there is different interaction phases within these two interaction mechanisms. These interaction phases appear as function of time and as function of peak intensity of laser beam. Limit peak intensity divides interaction mechanism from one-phase interaction into dual-phase interaction.

Nowadays, lasers are applied in many industrial processes: the most developed technologies include such processes as laser welding, hybrid welding, laser cutting of steel, etc. In addition to laser processing of metallic materials, there are also many industrial applications of laser processing of non-metallic materials, like laser welding of polymers, laser marking of glass and laser cutting of wood-based materials. It is commonly known that laser beam is suitable for cutting of paper materials as well as all natural wood-fiber based materials. This study reveals the potential and gives overview of laser application in processing of paper materials. In 1990's laser technology increased its volume in papermaking industry; lasers at paper industry gained acceptance for different perforating and scoring applications. Nowadays, with reduction in the cost of equipment and development of laser technology (especially development of CO 2 technology), laser processing of paper material has started to become more widely used and more efficient. However, there exists quite little published research results and reviews about laser processing of paper materials. In addition, forest industry products with pulp and paper products in particular are among major contributors for the Finnish economy with 20% share of total exports in the year 2013. This has been the standpoint of view and motivation for writing this literature review article: when there exists more published research work, knowledge of laser technology can be increased to apply it for processing of paper materials.

Laser technology has been used in industrial processes for several decades. The most advanced development and implementation took place in laser welding and cutting of metals in automotive and ship building industries. However, there is high potential to apply laser processing to other materials in various industrial fields. One of these potential fields could be paper industry to fulfill the demand for high quality, fast and reliable cutting technology. Difficulties in industrial application of laser cutting for paper industry are associated to lack of basic information, awareness of technology and its application possibilities. Nowadays possibilities of using laser cutting for paper materials are widened and high automation level of equipment has made this technology more interesting for manufacturing processes. Promising area of laser cutting application at paper making machines is longitudinal cutting of paper web (edge trimming). There are few locations at a paper making machine where edge trimming is usually done: wet press section, calender or rewinder. Paper web is characterized with different moisture content at different points of the paper making machine. The objective of this study was to investigate the effect of moisture content of paper material on laser cutting parameters. Effect of moisture content on cellulose fibers, laser absorption and energy needed for cutting is described as well. Laser cutting tests were carried out using CO2 laser.

We report the use of a laser-based fabrication process in the creation of paper-based flow-through filters that when combined with a traditional lateral flow immunoassay provide an alternative pathway for the detection of a pre-determined analyte over a wide concentration range. The laser-patterned approach was used to create polymeric structures that alter the porosity of the paper to produce porous flow-through filters, with controllable levels of porosity. When located on the top of the front end of a lateral flow immunoassay the flow-through filters were shown to block particles (of known sizes of 200 nm, 500 nm, 1000 nm and 3000 nm) that exceed the effective pore size of the filter while allowing smaller particles to flow through onto a lateral flow immunoassay. The analyte detection is based on the use of a size-exclusive filter that retains a complex (∼3 μm in size) formed by the binding of the target analyte with two antibodies each of which is tagged with different-sized labels (40 nm Au-nanoparticles and 3 μm latex beads), and which is larger than the effective pore size of the filter. This method was tested for the detection of C-reactive protein in a broad concentration range from 10 ng/ml to 100,000 ng/ml with a limit-of-detection found at 13 ng/ml and unlike other reported methods used for analyte detection, with this technique we are able to counter the Hook effect which is a limiting factor in many lateral flow immunoassays.

In this study, we demonstrate up to 30% increase in power density of carbon paper electrodes for vanadium redox flow batteries (VRFB) by introducing perforations into the structure of electrodes. A CO 2 laser was used to generate holes ranging from 171 to 421 μm diameter, and hole densities from 96.8 to 649.8 holes cm −2 . Perforation of the carbon paper electrodes was observed to improve cell performance in the activation region due to thermal treatment of the area around the perforations. Results also demonstrate improved mass transport, resulting in enhanced peak power and limiting current density. However, excessive perforation of the electrode yielded a decrease in performance due to reduced available surface area. A 30% increase in peak power density (478 mW cm −2 ) was observed for the laser perforated electrode with 234 μm diameter holes and 352.8 holes cm −2 (1764 holes per 5 cm 2 electrode), despite a 15% decrease in total surface area compared to the raw un-perforated electrode. Additionally, the effect of perforation on VRFB performance was studied at different flow rates (up to 120 mL min −1 ) for the optimized electrode architecture. A maximum power density of 543 mW cm −2 was achieved at 120 mL min −1 .

The combined de-inking technology of ultrasonic, UV irradiation and enzymatic methods was introduced into the de-inking process of HP laser printed paper. The purpose was to reduce the consumption of alkali or even preprocess without alkali absolutely for the purpose of environment protection. The de-inking effects of cellulase, amylase, lipase and their mixture were compared and the experiment results showed that combined enzymes of cellulase and amylase have the best de-inking efficiency which has a 12% increment of brightness. The de-inking efficiencies of several different de-inking technologies were compared, which can provide basis to establish combined de-inking technologies.

Using a molecular fluorine laser at 157 nm foxing stains were removed successfully from a 16th century old paper. Laser cleaning of stains and foxing from old paper manuscripts is far more effective at 157 nm in comparison to different wavelengths without leaving any yellowish after-effect on the paper. This is because at 157 nm illumination of old paper, complete bond breaking of all the organic molecules of the paper is taking place. Mass spectroscopy at 157 nm and for moderate laser intensities up to 1 mJ/cm 2 of old paper suffering from foxing indicate organic matter disintegration to small photofragments atomic, diatomic or triatomic, which are flying apart with supersonic speed. In addition high spatial resolution energy dispersive X-ray system (EDXS) analysis over the effected areas indicate the presence of iron, suggesting that biological activity is taking place preferentially in paper areas containing iron.

In this work we describe the design of our simulation tool for solid state lasers. The software is based on modules to simplify several complex processes. Primarily, the adaptation of laser physics (e.g. thermal lensing, optical wave) with the appropriate simulation technique. Another aspect is to provide the possibility of exchanging the applied calculation methods or even to change the representation of the computational domain on demand.

This paper reports the effects of multipass laser ablation over large areas and single lines of multiple layered coloured inks which have been printed upon ordinary white wood pulp paper. The aim of the work is to investigate the characteristics and feasibility of selectively removing subsequent layers to reveal different coloured inks and ultimately to generate a full coloured image with a tactile quality. An image generated in such a way would be considered to have features for anti-counterfeiting by colour copying. Ablation was performed using a Q-switched Nd:YAG laser. The results show that it is possible to selectively expose cyan, magenta and yellow layers, respectively, with repeated passes of the laser beam. SEM and colour analysis were carried out to examine the effect of laser ablation on the colour properties of the pigments. It was found that under the fundamental mode of the laser (1.06 μm wavelength) and a pulse width of 8 μs, the colours exposed by laser ablation were paler than those of the original prints and that the laser-treated surface is highly porous. An evaporation mechanism is proposed, whereby the laser energy is absorbed physically into the ink layers which then sublime, causing the pock marked surface.

High-intensity photodecomposition of 2-methoxyphenols using 248 nm laser excitation leads to the formation of small yields of ortho-quinones through the intermediacy of phenoxyl radicals, which undergo photocleavage of the O C bond. This process was studied using the laser-drop technique and the products were characterized by fluorescence spectroscopy following derivatization with 1,2-phenylenediamine. It is suggested that, given the long lifetime (several days) of related lignin-derived phenoxyl radicals in paper, similar processes may be partially responsible for quinone-mediated color development in papers manufactured from high-yield pulps.

A conventional problem of paper handling in a page-printing printer is to design a reliable paper path. Sometimes, this also affects the printing quality. The nonlinear theory of elastica has often been used to model paper deflection shape and to predict the paper path between some guiding rollers. The present paper proposes another method that can solve this problem more efficiently. Considering a piece of paper as a nonlinear beam, finite element analysis with geometric nonlinearity and manipulating the contact gap element between paper and guiding surfaces can be used to simulate the large-deflection behavior of paper. In this paper, the paper path in the vicinity of an OPC (organic photoconductive) drum is investigated with a general purpose finite element package. The effect of the electrostatic force between the OPC drum and the paper is considered, and the deformed shape of the paper for different forces lengths is obtained. According to those results an appropriate paper guide is added for an exact paper path.

Strongly luminescent fingerprints can be produced on paper by initial treatment of the latent print with the chemical reagent NDB chloride (4-chloro-7-nitrobenzofurazan), followed by excitation with a 150-W xenon arc lamp filtered to transmit light in the 475-nm spectral region. The fingerprint quality and ridge detail obtained using the xenon arc lamp was equal to that obtained using a 3-W argon ion laser. The marked cost and operational advantages of the xenon arc lamp clearly offsets the small increased photographic exposure time (about 6-fold) needed to obtain photographic records with this light source compared with the laser. Each source produces fluorescent images suitable for visual examination of test objects, with the xenon lamp requiring less stringent eye protection facilities than the laser. Some of the limitations of this reagent are discussed.

In banknote production, several security features are introduced into banknotes, including perforation of organic substrates like paper, polymer or their composites. This paper describes a comparative study about efficiency and quality aspects of laser drilling processes of organic substrates with different laser systems. The substrates investigated are cotton-based paper, Guardian™ (Biaxially Oriented Polypropylene) and two composite substrates composed of cotton paper and polymer (Durasafe™ and Hybrid™). The used laser wavelengths are 515 nm, 1060/1070 nm and 2940 nm. Laser systems with pulse durations covering the ultra-short pulse regime (ps), nanosecond pulses (ns) and microsecond pulses (µs) were used. This article gives an overview of this topic, deals with the tasks and challenges in this special field of laser manufacturing and compares different laser systems with respect to drilling quality and energy specific volume.

In the packaging industry, cutting dies are used to process paper based material. The dies are mainly manufactured via steel strip principle, which consists of many manual steps and is difficult to automate. Laser material processing represents a promising approach to simplify manufacturing. This study realized additively manufactured cutting edges post-processed by laser ablation to achieve a defined final profile shape. First verification shows that laser ablation appears to be attractive for finishing of additively manufactured cutting edges.

We made an attempt to form a high quality epitaxial zinc oxide, diamond-like-carbon and graphene oxide composite thin-film on device substrate p -Si(1 0 0) using third-harmonic (Nd:YAG Ultraviolet) laser at single footstep. Pulsed laser deposition (PLD) technique using 366 nm (energy~150 mJ), vacuum 10 −6 mbar has been used to grow these films in reactive gas oxygen with argon (O 2 |Ar) ambiance. Synthesized thin-films were investigated systematically by fingerprint technique of confocal micro-Raman and field emission studies. As synthesized pure ZnO, nanocomposite thin films like DLC/ZnO and GO/ZnO shows the enhanced field emission (F-E) performances in this present study.

We demonstrate a laser-based technique to directly synthesize few layer graphene on quartz substrates without using any metal catalyst. In our approach, a photoresist S-1805 (from Shipley Comp.) film coated on quartz wafers was heated, and then decomposed, by irradiation of a continuous-wave laser. The carbon atoms from the photoresist were dissolved in the molten quartz, and then extracted to form graphene when the temperature of the quartz was decreased. Raman spectroscopy shows the as-produced graphene is two to three layers thick. This laser-based method will provide a new approach and platform for applications of graphene-based devices. (C) 2012 Elsevier Ltd. All rights reserved.

In principle, this paper suggests powerful laser technology as a promising instrument that can be experimentally useful to control the lifetime and branching ratio for an unstable particle decay. In a recent paper [ arXiv:2101.00224 ], we calculated theoretically the W − -boson leptonic decay ( W − → l − ν l ) in the presence of a circularly polarized laser and we showed that the laser significantly contributed to the diminution of the leptonic decay rate. In this paper, as a continuation of the previous one, we mainly deal with the theoretical calculation of the W − -boson hadronic decay ( W − → q q ′ ) and we combine the analytical results obtained in both papers to examine the effect of an intense laser, in terms of its field strength and frequency, on the three measurable quantities in W − -boson decay (total decay rate, lifetime and branching ratios). It was found that the laser has notably contributed to the reduction of the total decay rate leading to a longer lifetime. Most importantly, the two branching ratios (one for leptons and the other for hadrons) are affected (increased or decreased) by the presence of a strong external electromagnetic field. Combined together, these two complementary works may provide an in-depth and comprehensive study that would be useful for any experimental investigation in the future.

In order to maximize the lethality and reversibility of the non-lethal laser weapons (NLLW) at the same time and thus provide a theoretical basis for the R&D of laser weapons in the future, this paper accurately analyzed the limiting biological dose of irreversible damage to human skin caused by the NLLW. Firstly, based on the burn theory in medicine and the actual tactical background, this paper redefines the evaluation criteria of the limiting laser dose of NLLW to the human body. Secondly, on the basis of anatomical knowledge, a 5-layer finite element model (FEM) of superficial skin is proposed, constructed and verified, which can accurately describe the limiting reversible damage. Based on the optimized Pennes bioheat transfer equation, the diffusion approximation theory, the modified Beer-Lambert law, the Arrhenius equation, and combined with dynamic thermophysical parameters, this paper highly restored the temperature distribution and accurately solved the necrotic tissue distribution inside the human skin irradiated by 1064 nm laser. Finally, it is concluded that the maximum human dose of the 1064 nm NLLW is 8.93 J/cm2, 8.29J/cm2, and 8.17 J/cm2 when the light spots are 5 mm, 10 mm and 15 mm, respectively, and the corresponding output power of the weapon is 46.74 W,173.72 W and 384.77 W. Simultaneously, the temperature and damage distribution in the tissue at the time of ultimate damage are discussed from the axial and radial dimensions, respectively. The conclusions and analysis methods proposed in this paper are of great guiding significance for future research in military, medical and many other related fields.

The paper presents the possibilities of, and methods for, acquiring, analysing and processing optical signals in order to recognise, identify and counteract threats on the contemporary battleground. The main ways electronic warfare is waged in the optical band of the electromagnetic wave spectrum have been formulated, including the acquisition of optical emitter signatures, as well as ultraviolet (UV) and thermal (IR) signatures. The physical parameters and values describing the emission of laser radiation are discussed, including their importance in terms of creating optical signatures. Moreover, it has been shown that in the transformation of optical signals into signatures, only their spectral and temporal parameters can be applied. This was confirmed in experimental part of the paper, which includes our own measurements of spectral and temporal emission characteristics for three types of binocular laser rangefinders. It has been further shown that through simple registration and quick analysis involving comparison of emission time parameters in the case of UV signatures in “solar-blind” band, various events can be identified quickly and faultlessly. The same is true for IR signatures, where the amplitudes of the recorded signal for several wavelengths are compared. This was confirmed experimentally for UV signatures by registering and then analyzing signals from several events during military exercises at a training ground, namely Rocket Propelled Grenade (RPG) launches and explosions after hitting targets, trinitrotoluene (TNT) explosions, firing armour-piercing, fin-stabilised, discarding sabots (APFSDS) or high explosive (HE) projectiles. The final section describes a proposed model database of emitters, created as a result of analysing and transforming the recorded signals into optical signatures.

The laser technology has made remarkable progress over the past couple of decades. It is being widely employed in diverse domains, such as holography, space sciences, spectroscopy, medical sciences, micro and power electronics, industrial engineering, and most distinctively, as directed energy military weapons. Owing to their active transmissions, laser systems are similar to microwave radars to some extent; however, unlike conventional radars, the laser operates at very high frequencies thus making it a potent enabler of narrow-beam and high energy aerial deployments, both in offensive and defensive roles. In modern avionics systems, laser target indicators and beam riders are the most common devices that are used to direct the Laser Guided Weapons (LGW) accurately to the ground targets. Additionally, compact size and outstanding angular resolution of laser-based systems motivate their use for drones and unmanned aerial applications. Moreover, the narrow-beam divergence of laser emissions offers a low probability of intercept, making it a suitable contender for secure transmissions and safety-critical operations. Furthermore, the developments in space sciences and laser technology have given synergistic potential outcomes to use laser systems in space operations. This paper comprehensively reviews laser applications and projects for strategic defense actions on the ground or in space. Additionally, a detailed analysis has been done on recent advancements of the laser technology for target indicators and range-finders. It also reviews the advancements in the field of laser communications for surveillance, its earlier state of the art, and ongoing scientific research and advancements in the domain of high energy directed laser weapons that have revolutionized the evolving military battlefield. Besides offering a comprehensive taxonomy, the paper also critically analyzes some of the recent contributions in the associated domains.

Potholes are bowl-shaped distresses that negatively influence driving safety. Using 3D line laser technology, a high-resolution pavement profile can be acquired to derive pothole properties. This paper presents a novel method to measure pothole properties comprehensively and precisely by using 3D line laser data. A laboratory test was performed on a simulated pothole to validate the reliability of proposed method. The test results indicate that the relative error of pothole properties measurement ranges from 3.66% to 4.78%. And the small standard deviation shows good repeatability. In addition, this paper proposes that the longitudinal spacing between two adjacent transverse profiles is sensitive to pothole property measurements, and the optimum spacing should be less than 2 mm to accurately measure pothole properties. Using the optimum spacing, 2 field potholes data were collected on interstate way 107, Xi’an, Shaanxi Province. The field test results have shown that the relative error of pothole properties measurement can be less than 8%, which is sufficiently accurate for practical applications. This paper demonstrated that 3D line laser is very promising to provide a reliable measurement results for pothole properties.

This article is the second in a four-part series of articles providing an overview of the challenges and opportunities in microscale additive manufacturing (AM) processes with applications in fabrication of high precision micro/nano-products. Laser-based microscale additive manufacturing processes are discussed this article. Compared to the other AM processes, laser-based processes provide several unique advantages, especially in terms of a wide variety of processable materials and high volumetric throughputs. The processes discussed in this paper can fabricate complex microscale features with minimum resolutions ranging from hundreds of nanometers to hundreds of microns. However, there are several fundamental limits and trade-offs which hinder the scalability of these processes. The paper discusses the limits to the materials, resolution, geometry, and volumetric throughput and proposes approaches to mitigate these limits and improve the scalability of laser-based microscale AM processes.

This paper presents new measurements of species concentrations, temperature and mixture fraction in selected regions of a turbulent ethanol spray flame. The line-Raman–LIF–CO OH setup developed at the Sandia's Combustion Research Facility is utilised to probe regions of a spray flame where laser breakdown of liquid droplets is avoided and the remaining interferences can be corrected. The spray flame is stabilised on the piloted Sydney needle spray burner, where axial translation of the liquid injecting needle in the air-blast stream can transition the spray from dilute to dense. The solution to obtaining successful measurements is found to be multifaceted and includes: the appropriate selection of flame conditions; high sensitivity of the Raman detection system permitting reduced laser energies; development of a pre-processing algorithm to reject strong droplet interferences; and application of the hybrid matrix inversion method combined with wavelet denoising to account for interference corrections and noise at the very low signal levels obtained. Unique and necessary for the successful measurements reported in this paper, a pre-processing algorithm is outlined that removes data points corrupted with strong interferences from droplets. These interferences arise from a range of sources, but the most intense are due to the laser interaction with surrounding mist or liquid fragments, such that measurements near the jet centreline are corrupted and hence discarded. Reliable measurements of mixture fraction, temperature obtained from the sum of the species number densities, and species mole fractions are reported for regions in the flames sufficiently far from the centreline. The paper demonstrates the feasibility of the judicious use of Raman scattering in turbulent spray flames, the results of which will be extremely useful for validating numerical simulations.

International audience; This feature article highlights the recent advances on the lanthanide-activated nanoparticles prepared by pulsed laser ablation in liquids (PLAL). In the past decade, rare-earths-activated nanoparticles have been recognized from various applications including lots of high-tech products, green technologies, bioimaging and medical utilization. To obtain inorganic nanoparticles with different morphologies and sizes, pulsed laser ablation in liquids is a green and versatile technique. In this paper, a survey of the nanoparticle's formation during the laser ablation in the liquids is first introduced. We focus on the control of the size and morphology through proper laser parameters, choice of the reaction solution and proper surfactants. In the last part of the paper, we successfully prepared persistent luminescent SrAl 2 O 4 : Eu 2+ , Dy 3+ by laser ablation in liquids and their optical features are investigated.

The variances in local processing conditions during Selective Laser Melting (SLM), a powder bed Additive Manufacturing (AM) process, can cause defects that lead to part failure. The nature of SLM permits in-situ monitoring of radiometric signals emitted from the part surface during the process, including optical emission from excited alloying elements. Using Optical Emission Spectroscopy (OES) to measure the spectral content of light emitted gives insight into the chemistry and relative intensities of excited species vaporized during SLM processing. The contribution from investigating the use of in-situ OES to gain information about local processing conditions during SLM is reported in this paper. A spectrometer is split into the SLM system laser beam path to measure visible light emitted from the melt pool and plume during the processing of 304L stainless steel. The in-line configuration allows signal collection regardless of the laser scan location. The spectroscopic information is correlated to the melt pool size and features of SLM samples for various build conditions (i.e., process parameters, build chamber atmosphere type, and pressure).The limitations that exist in OES implementation for certain build chamber conditions are discussed. The results in this paper are initial progress towards the use of OES in SLM part qualification and controls applications.

Ultrashort-pulsed lasers allow a precise, low thermal damage and material independent micro processing. However the full potential of ultrashort pulsed lasers with their currently available laser power cannot be used due to limitations in ablation rate per pulse keeping the high quality in ablation. Beside scaling up by multi spot technology, the application of ultrashort pulse bursts is another possibility to increase the ablation rate. In this paper a newly developed ultrashort pulsed laser with a seeder frequency of 500 MHz has been investigated in cylinder micro engraving application. The laser offers the possibility to control the shape of a burst sequence in amplitude and timing. The influence of the pulse sequence on the ablation rate and quality in combination with the different metals has been investigated. The pulse burst frequency has been changed between 1 - 5 MHz with a scanning speed of 16 m/s. The pulse to pulse overlap at the work piece was adjusted from 0% to 90%. Comparing to single pulse ablation the ablation rate with GHz pulse burst is increased by factor 2.2. The surface roughness is Ra = 0.38µm with GHz pulse burst, whereas the roughness is Ra = 1.423 µm with single pulse. In this paper experimental ablation results and quality aspects will be presented and discussed.

This paper discusses fatigue life prediction of laser and mechanically formed commercially pure grade 2 titanium alloy plates. It should be noted that predicting fatigue damage for structural components is a complex issue that needs various factors involved in fatigue analysis to be taken into account. This paper looked at available fatigue life prediction theories as a start which then helped formulate and develop the fatigue life prediction analysis used in this study. The predicted fatigue life was not off the mark as it also incorporated the effects of residual stresses which are usually disregarded in studies of this nature. The validity of the fatigue life prediction concept is shown with the aid of calculations versus actual fatigue data results. The results show fatigue life prediction that is stable and less erratic on certain irradiation parameters, while other formed components behaved in a predictable manner. Fatigue life prediction analysis is a challenging undertaking and the behavior of benchmarking components is explained and possible reasons for this elucidated.

In many industrial applications, especially for automotive, aerospace and electronics, laser welding is the preferred joining process due to its high flexibility, short process time and high precision. In conventional single-mode laser welding, the laser beam is fine (typical spot diameter 10 – 40 µm) producing a very narrow weld profile. Wobbling or oscillating the laser beam ensures the weld width and depth of penetration can be achieved in a controlled manner. The wobble technique is most useful for highly conductive and reflective materials as it helps to reduce the spatter formation, back-reflection and instability with the laser. Joining with an overlap configuration created using the wobble technique have been most commonly investigated. But the fillet edge weld is considered more useful for sealing applications without the need for additional filler material. This paper investigates the feasibility of producing fillet edge welds, using the wobble technique, to join 0.3 mm thin aluminium to 1.5 mm thick aluminium sheet. A 1.0 kW CW IR laser was used to produce the fillet edge welds aiming for both joining and sealing applications. The effects of process parameters including laser power, welding speed, wobble amplitude and wobble frequency were studied to evaluate the weld quality. Joint strength and weld microstructural features including penetration depth and interface width were evaluated as indicators of weld quality. The relations between the input laser process parameters and output quality indicators were identified and the weld quality was classified into under-weld, good-weld and over-weld categories. In the case of the good-weld condition, average lap shear strength was around 418.64 N. The results suggested that preferred penetration depth and interface width can be obtained by controlling the laser power, welding speed and wobble amplitude. Overall, this paper demonstrates the feasibility of obtaining good fillet edge joint using laser wobble technique.

This paper presents a robust multivariable predictive control for laser-aided powder deposition (LAPD) processes in additive manufacturing. First, a novel control-oriented MIMO process model is derived. Then, the objective of achieving desired geometrical and thermal properties is formulated as one of generating and tracking nominal reference profiles of layer height and melting pool temperature. This is accomplished via a nonlinear model predictive control with guaranteed nominal stability. Furthermore, a local ancillary feedback law is derived to provide robustness to bounded uncertainties. The paper verifies the effectiveness of the proposed control via a case study on a laser cladding process.

International audience; This paper presents a novel approach for the measurement of vapor fuel concentration at engine relevant conditions for the investigation of preferential evaporation in multicomponent fuel GDI sprays.The result is achieved by combining in synergy two different tools: i) two-tracer laser induced fluorescence (2T-LIF), a laser diagnostics capable of investigating qualitatively the preferential evaporation by the simultaneous employ of two fluorescent tracers and, ii) a numerical model capable of relating the tracers concentration to the vapor fuel composition.In order to make this approach reliable for future spray application, this paper presents in details the methodology, including the definition of the surrogate fuel and the tracers. Moreover, results of a fuel evaporation experiment in a simplified environment are presented to validate the numerical model and to assess the uncertainties associated to the technique in spray applications.The evaporation experiment includes parametric variations of the effect of system pressure (1-5-10 bar), and ethanol concentration (0%, 20% and 85% vol.), exploring problematic relevant to real GDI engines.The experimental results provided also fundamental understanding of the preferential evaporation process.Ethanol is observed to form an azeotrope with lighter compounds segregating the evaporation of the heaviest compounds at the end of the evaporation process.Finally, the systematic error related to the calculation of vapor phase composition related to the thermodynamic model approximations was assessed for GDI relevant application. The results indicated a very low impact on the final results and discrepancies lower than 5%.

The possibilities for detecting defects in multilayer carbon composites occurring as a combination of layers of carbon fiber fabric with thin layers of epoxy resin (CFRP) are presented in this paper. The most common defect in this type of structure is delamination . For non-destructive testing of CFRP samples with deliberately introduced defects, infrared thermography with laser thermal stimulation was used and both computer numerical simulations (using the ThermoCalc program) and experimental tests were carried out. In the experimental testing, a semiconductor laser with a wavelength of 808 nm and a maximum power of 32 W was used for thermal stimulation. Changes of temperature field on the surface of the test sample were recorded with a thermal camera, FLIR 7600 SC. Both pulsed and lock-in thermography methods were used, and this paper presents selected results, together with their analysis. The results presented in this paper show that it is possible to use a laser as a heating source in thermographic non-destructive testing of CFRP composite.

At present, wired and wireless charging methods for electric vehicles (EVs) have a number of drawbacks including short charging ranges and long charging times. Laser power transfer (LPT) is a wireless power transfer technique which can be used for UAV (unmanned aerial vehicle) and satellite charging. Recent developments in photovoltaic cells and laser technology allows the transfer power using light which might overcome many of the issues related with other charging methods. In this paper, we describe the design and implementation (in MATLAB) of a novel, high-power charging method using a laser (monochromatic light) to charge electric vehicles. The paper examines the overall efficiency of the LPT for a various input power-level. In addition, it also examines the safety and the possible charging infrastructure for LPT technology. Using this technique, we believe that an overall efficiency of 10-37% can be achieved using existing technology.

This paper develops an analytical model of temperature in Laser Powder Bed Fusion (LPBF) considering the geometrical effect of the build part, which is reflected by the part size and shape. The model is established based on the moving point heat source under a semi-infinite medium. A modified coefficient is utilized to calibrate the temperature along the build direction. The heat sink is adopted to consider the heat loss at the edge of the build part, and the superposition method is applied to calculate the multi-tracks effect of the laser beam. The material thermal properties are dependent on the temperature, and an iteration method is utilized to obtain the dynamic stable melt pool during the process. To validate the proposed model, the experimental data in the published paper are compared with the model predictions. Good agreement is found about the melt pool size. Based on the verified model, a sensitivity analysis of temperature with respect to the laser process parameters, the material properties, and the geometry of the build part is discussed. Both the depth and width of the melt pool have a negative relationship with the size of the part within the explored range. It is also shown that the size of the melt pool has a negative correlation with the length of the previous track, which is determined by the shape of the build part.

It has been shown that quality of components built using selective laser sintering (SLS) are strongly affected by the thermal history of the building process. Temperature variations of a few degrees across the powder surface can alter the mechanical properties of components and render them unsuitable for their intended purpose. Therefore, to improve the quality of SLS components and ease their adoption into the marketplace, temperature fluctuation issues must be addressed. Some success has been demonstrated in the past at reducing temperature non-uniformity by improving the heater system that pre-heats the polymer powder prior to sintering with the laser. This paper will cover a complimentary approach of actively controlling laser fluence on the powder surface based on infrared temperature measurements. By controlling the amount of energy input by the laser, a high level of control over the final part temperature can be achieved and uniformity can be improved. This paper will cover development of the feed-forward control system and will present results showing that for constant cross-section specimens, a 45% improvement in ultimate flexural strength standard deviation was achieved.

While various techniques have been developed for manipulation of biological cells or micro-objects using optical tweezers, the performance and feasibility of these techniques are mostly dependent on the physical properties of the target objects to be manipulated. In these existing techniques, direct trapping and manipulation of the manipulated objects using laser traps are performed, and therefore, existing techniques for optical manipulation are not capable of coordinating and manipulating various types of objects in the micro-world, including untrappable micro-objects, relatively large micro-objects, and laser sensitive biological cells. In this paper, a cooperative control technique is proposed for coordinative and mobile manipulation of multiple microscopic objects using micro-hands with multiple laser-driven fingertips and robot-assisted stage control. Several virtual micro-hands are formed by coordinating multiple optically trapped micro-particles that serve as the laser-driven fingertips, and then utilized for individual and coordinative manipulation of the target micro-objects. Simultaneously, global transportation of all the grasped target objects is performed by controlling the robot-assisted stage. While it is difficult to design multi-fingered hands in micro-scale due to scaling effect, this paper presents the first result on cooperative and mobile manipulation of multiple micro-objects using multiple micro-hands with laser-driven fingertips and robot-assisted stage control. In this paper, a primary study on repositioning strategy of the laser-driven fingertips is also introduced to allow the fingertips in a grasping formation to be repositioned. Rigorous mathematical formulations and solutions are derived to achieve the control objective, and experimental results are presented to demonstrate the effectiveness of the proposed control technique. Accepted version

In this paper, the results of numerical experiments verifying a novel setup for laser beam profiling are presented. The experimental setup is based on infrared thermography and includes laser beam illuminating a thin metal plate. The method allows to determine four parameters of the short high-power laser pulse, namely the Super-Gaussian profile coefficient, laser power, pulse start time and duration. The unknown parameters are retrieved based on temporal and spatial temperature distributions at the rear side of the illuminated plate. The applied inverse method is based on Levenberg-Marquardt technique and is implemented in the GNU Octave environment. Solutions of the forward problem are obtained numerically, with the aid of three-dimensional transient heat transfer model implemented in the commercial software ANSYS Fluent. The paper presents the results of the sensitivity analysis as well as calibration and verification of the developed inverse algorithm through application of numerically-generated simulated (artificial) experimental data instead of the physical one. Strengths and weaknesses of the applied approach are widely discussed.

In plasma wakefield accelerators (e.g. AWAKE) the proton bunch self-modulation is seeded by the ionization front of a high-power laser pulse ionizing a vapour and by the resulting steep edge of the driving bunch profile inside the created plasma. In this paper, we present calculations in 2D linear theory for a concept of a different self-modulation seeding mechanism based on electron injection. The whole proton bunch propagates through a preformed plasma and the effective beam current is modulated by the external injection of a short electron bunch at the centre of the proton beam. The resulting sharp edge in the effective beam current in the trailing part of the proton bunch is driving large wakefields that can lead to a growth of the seeded self-modulation (SSM). Furthermore, we discuss the feasibility for applications in AWAKE Run 2. In plasma wakefield accelerators (e.g. AWAKE) the proton bunch self-modulation is seeded by the ionization front of a high-power laser pulse ionizing a vapour and by the resulting steep edge of the driving bunch profile inside the created plasma. In this paper, we present calculations in 2D linear theory for a concept of a different self-modulation seeding mechanism based on electron injection. The whole proton bunch propagates through a preformed plasma and the effective beam current is modulated by the external injection of a short electron bunch at the centre of the proton beam. The resulting sharp edge in the effective beam current in the trailing part of the proton bunch is driving large wakefields that can lead to a growth of the seeded self-modulation (SSM). Furthermore, we discuss the feasibility for applications in AWAKE Run 2.

This paper reviews the main issues arising from the use of fiber Bragg gratings as temperature sensors in the presence of significant thermal gradients. These conditions occur for example during laser thermal ablation of tumors. In particular, the paper focuses on the identification of the grating position along the fiber, which represents one of the main uncertainty contributions. A novel experimental setup for the grating center localization is proposed and the corresponding characterization procedure has been devised. The setup is built in such a way as to generate reproducible linear temperature distributions. Tests carried out using a sensor prototype have shown that the grating position can be found with a standard uncertainty of 0.3 mm.

Many applications in additive manufacturing involve the dynamic deposition of powders and the in-flight heating of such material by a laser. In order to characterize such systems, the Discrete Element Method (DEM) is employed. Specifically, this paper focuses on the initial stages of this process by developing a modular discrete-element type multiphysics simulation method for the particle dynamics and heating by a laser and detailed thermal behavior. The objective is to provide researchers with a framework to construct computational tools for this growing industry. In order to achieve this, from a simulation standpoint, the overall particle-mixture system is constructed by coupling submodels for each primary physical process (dynamics and heating) together. An iterative staggering scheme is developed whereby, within every time step, each individual particle is solved “freezing” the state of the remaining multiparticle system. The state of the particle is then updated and the algorithm moves to the next particle in the system and the process is repeated. The overall process sweeps through the entire system repeatedly until convergence is achieved in an appropriate norm. As the system evolves, an error estimate dictates the time-step size that is needed to induce convergence to below an appropriate error level. Thus, the process can be considered as an implicit time-stepping scheme, which is combined with an (internal) iterative staggering process. In order to control rates of convergence within a time-step, the algorithm adjusts the time-step size. If the iterative process does not converge within a desired number of iterations, below an error tolerance, the time-step is reduced. The degree of time-step reduction is determined by utilizing an estimate of the spectral radius of the coupled system. Since the construction of model and solution process is modular, one can easily replace physical submodels with other choices, making it easy to numerically experiment with a variety of models. Qualitative and quantitative analyses are provided, as well as three-dimensional numerical examples. This paper addresses the first of two overall “macrostages” of a complex manufacturing process with DEM. The first stage, addressed in this paper, concentrates on dry-powder materials, which are of a discrete particulate character, using DEM to characterize the deposition and in-flight particle heating. Other papers of the author (Zohdi, 2010, 2013, 2014, 2015 [81,82], 2008) have addressed stage two, namely phase transformations, curing (cooling) and stress analysis, using more appropriate continuum and hybrid DEM-continuum approaches.

In this paper a new contribution to the optimization of processing parameters in the process of laser sharpening grinding wheels is presented. In the establishment of the three-dimensional heat conduction model, the laser heat source model is improved and the temperature field of the pulsed laser ablation material is obtained. The effects of laser power, laser line spot overlap ratio and laser scanning track overlap ratio on the sharpening efficiency and accuracy have been studied through the established numerical model. Like what happened in the actual machining process, the morphology of the bond material surface after laser sharpening was obtained by the simulation. The results show that the optimal values of laser power, laser line spot overlap ratio and laser scanning track overlap ratio are 20 W, 70%, and 70%, respectively. The simulation results have been verified and compared with the experimental results, revealing a good correlation between the simulation and experimental data. In a word, the numerical model established in this paper can be conveniently used in the optimization of the process parameters in the laser sharpening grinding wheel.

Although TiB reinforced titanium matrix (TiB-Ti) composites exhibit superior wear resistance and strength, they still demonstrate severe problems resulted from lowered toughness and ductility, as compared with titanium and its alloys. To reduce these problems, this paper tailors a three-dimensional quasi-continuous network (3DQCN) microstructure within TiB-Ti composites by in-situ laser deposition-additive manufacturing process. Results show that the laser power has great impacts on the formation of 3DQCN microstructure and the 3DQCN microstructure is beneficial to both strengthening and toughening effects on TiB-Ti composites. To have a quantitative understanding of strengthening effects, this paper, for the first time, has modeled the yield strength of TiB-Ti composites with 3DQCN microstructure.

We present a new method to create ultrashort electron pulses by integrating a photoconductive switch with an electrostatic deflector. This paper discusses the feasibility of such a system by analytical and numerical calculations. We argue that ultrafast electron pulses can be achieved for micrometer scale dimensions of the blanker, which are feasible with MEMS-based fabrication technology. According to basic models, the design presented in this paper is capable of generating 100 fs electron pulses with spatial resolutions of less than 10 nm. Our concept for an ultrafast beam blanker (UFB) may provide an attractive alternative to perform ultrafast electron microscopy, as it does not require modification of the microscope nor realignment between DC and pulsed mode of operation. Moreover, only low laser pulse energies are required. Due to its small dimensions the UFB can be inserted in the beam line of a commercial microscope via standard entry ports for blankers or variable apertures. The use of a photoconductive switch ensures minimal jitter between laser and electron pulses.

This paper deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites that took place in the first two years of the H2020 CompInnova project which. The aim is a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. This will affect the increasing societal need for safer aircraft in the lowest possible cost, while new and effective techniques of inspection are needed because of the rapidly expanding use of composites in the aerospace industry.

The terahertz (THz) quantum cascade laser (QCL), first demonstrated in 2002, is among the most promising radiation sources in the THz region owing to its high output power and broad frequency coverage from ∼1.3 to ∼5.4 ​THz and sub-terahertz, without and with assistance of external strong magnetic field. The operation of THz QCLs, however, has thus far been limited to applications below room temperature. Recent advances in THz QCL research have principally focused on optimization of quantum design, fabrication, and growth techniques to improve the maximum operating temperature of THz QCLs; these efforts culminated in a recent demonstration of pulse-mode lasing at temperature up to 250 ​K. Research interests continue to be propelled as new maximum lasing temperature record are set, heating up the race to realize room-temperature operation of THz QCLs. This paper critically reviews key achievements and milestones of quantum designs, fabrication techniques, and simulation methods applicable to the high temperature operation of THz QCLs. In addition, this paper provides a succinct summary of efforts in this field to pinpoint the remaining challenges and provide a comprehensive picture for future trends in THz QCL research.

This paper presents a study on the incubation effect during fs-laser micromachining of gallium nitride films with three different wavelengths (1030, 515 and 343 nm) by varying the number of laser pulses applied per sample surface area and measuring the damage threshold fluence using the zero damage method. As we implemented the exponential defect accumulation model to the experimental incubation data, we determined the value of the incubation parameter of (0.02 ± 0.01) for 1030 nm, (0.07 ± 0.01) for 515 nm and (0.4 ± 0.1) for 343 nm. This shows that for excitation in the green and infrared spectral region, GaN requires approximately 100 overlapping pulses in order for the incubation to take place while, for ultraviolet excitation, the incubation was achieved faster, with the overlap of about 10 pulses. Furthermore, we compared our data for the single pulse damage threshold with a theoretical model that takes into account multiphoton and avalanche ionization. Our results indicate that at 343 nm and 515 nm, micromachining is dominated by multiphoton ionization, while at 1030 nm other effects, such as tunneling ionization, must also be contributing. Finally, we believe this paper brings relevant information on the fs-laser micromachining of GaN.