Search

The recently emergent laser induced graphene paper (LIGP) has endowed the large-scale assembly of 2D electronics with freestanding and multifunctional natures. Liquid sensors, a crucial component in next-generation smart devices, were developed in this report through LIGP technology. Attributed to the one-step process of computer-aided laser scribing, the new sensor was fulfilled easily with arbitrary 2D shapes, sizes and array modalities. In comparison to indirect sensing manners existed majorly in polymer binder/substrate enabled carbon devices, the novel LIGP sensors with self-supported graphitic structures evidently showed multiple superiorities, including faster response, greater reproducibility, and higher sensitivity for micro-volume liquid detections. Benefiting from the laser-process dependent structures, we further proved the tunable sensing characteristics relying dominantly on specific surface area, a critical factor for introducing capillary pressure to facilitate liquid infiltration and electrical disruption. Additionally, a dual-mode liquid-recognition strategy based on both time and speed was creatively proposed for identification of various liquids. With successful utilization of 5 × 5 LIGP array for mapping the distribution of different fluid emissions on composite structures, we highly anticipate the escalation of LIGP sensors for commercialization, roll-to-roll manufacturing, and multimodal safety-assurance applications.

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.

Paper-based supercapacitors have attracted more and more attention for high electrochemical performance. However, most of them adopt sandwiched structure. Here, we prepared planar polypyrrole (PPy) coated paper-based supercapacitors by applying simple laser carving assisted method. The planar device showed a significant performance improvement (13.9 mF/cm2) compared to the sandwiched device (12.3 mF/cm2). In addition, by adjusting the polymerization time of pyrrole, the device capacity can be further increased to 87.4 mF/cm2. We firmly believed that the laser carving assisted method has a significant role in promoting the development of flexible planar electronic devices.

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.

This work investigated the effect of a chelator-mediated bio-mimetic free radical treatment on repulping and flotation operations during the deinking of laser printed copy paper. A chelator-mediated free radical treatment was carried out at two different chemical levels and a two-step repulping method, which combined conventional alkaline repulping as well as free radical treatment, was also developed. Flotation trials were performed on each of these treated samples to separate ink particles. Results from image analysis and paper physical properties testing are presented, and the deinking efficiency for these different treatments is also compared. Results indicate that under properly controlled conditions, free radical treatment can perform better than conventional chemical deinking methods.

Paper-based laser induced fluorescence immunodevice for alpha fetoprotein (AFP) detection was developed in this work by using CdTe quantum dots (QDs) embedded silica nanoparticles as the signal enhancement label. A homemade laser induced fluorescence device with two optical fibres was used here for the fluorescence detection. Laser issued by a semiconductor laser light source (405 nm, 1 mW) was exposed to the paper-based chip with very lower background through an optical fiber and the fluorescence (542 nm) induced by laser was collected to a photomultiplier tube (PMT) through a glass fiber. The paper-based chip was fabricated by the wax-printing method and the antibody can be directly immobilized on the plasma treated paper surface. Then CdTe QDs embedded silica nanoparticles with the signal enhancement function was labeled on the signal antibody. After a sandwich-type immunoreaction, AFP was linearly detected in the range from 0.001 ng/mL to 20.0 ng/mL with a detection limit of 0.4 pg/mL. Laser induced fluorescence with the homemade device was for the first time applied on the paper-based chip with very higher sensitivity. What’s more, the proposed strategy opened a promising platform for sensitive monitoring of cancer biomarkers in biological analysis and medical diagnostics.

This study investigates why a silver nanoparticle (SNP)-induced surface-enhanced Raman scattering (SERS) paper chip fabricated at low successive ionic layer absorption and reaction (SILAR) cycles leads to a high SERS enhancement factor (7 × 10 8 ) with an inferior nanostructure and without generating a hot spot effect. The multi-layered structure of SNPs on cellulose fibers, verified by magnified scanning electron microscopy (SEM) and analyzed by a computational simulation method, was hypothesized as the reason. The pattern of simulated local electric field distribution with respect to the number of SILAR cycles showed good agreement with the experimental Raman intensity, regardless of the wavelength of the excitation laser sources. The simulated enhancement factor at the 785-nm excitation laser source (2.8 × 10 9 ) was 2.5 times greater than the experimental enhancement factor (1.1 × 10 9 ). A 532-nm excitation laser source exhibited the highest maximum local electric field intensity (1.9 × 10 11 ), particularly at the interparticle gap called a hot spot. The short wavelength led to a strong electric field intensity caused by strong electromagnetic coupling arising from the SNP-induced local surface plasmon resonance (LSPR) effects through high excitation energy. These findings suggest that our paper-based SILAR-fabricated SNP-induced LSPR model is valid for understanding SNP-induced LSPR effects.

A more noble and biocompatible Ti alloy was achieved at fluence of 140 J cm−2 where the implant indicated a higher degree of hardness (825HV), higher corrosion resistance (−0.21 V) and highest hydrophilicity (i.e. θc = 37°) compared with 70° of the control sample. These values corresponded to 58 and 39 mN m−1 of surface tension respectively. The laser treated samples at 140 J cm−2 showed higher wettability characteristics than mechanically roughened surface. Cell growth and their spreading condition in a specific area were analyzed by SEM and Image J Program software. Clearly, more cells were attached (1.2 × 105) to and spread (488 μm2) over the surface at 140 J cm−2 than in any other condition. Pathologically, the treated samples indicated no sign of infection.

Machine learning methods are being successfully applied in various domains of human activity, including optics. Can they become a universal instrument capable of improving user aspect of photonic devices? Is their application a necessary element of such improvement? Answers to fundamental questions arising from application of machine learning methods in ultrashort-pulsed lasers are discussed. Future prospects and current fundamental limitations of such methods are analysed.

Development of the flexible electronics, especially electronic skin, put forward new requirements for flexible substrates and sensing materials. Herein, using printing paper substrate and Bi2S3 microflowers, the high performance flexible laser detector is successfully fabricated. The laser detector has a flexible and fast response to 450, 532, 650 and 780 nm laser beams of different intensity. The flexible laser detector is able to measure as weak laser signal as 3.3 mW/cm2 at 450 nm. The mechanism of the photo response of laser detector based on Bi2S3 microflowers is discussed. Our work here opens up opportunities for the fabrication of flexible optoelectronic devices with quite high and stable spectral property.

We report a simple hydrochloric acid (HCl) impregnation method to substantially improve the lyophobicity of a paper against gallium-based liquid metal. Based on the HCl-impregnated paper, we also propose an extremely simple fabrication method of microfluidic channel for gallium-based liquid metal, Galinstan®. Due to its low cost, easy fabrication, and flexibility, recently paper has drawn attention as microfluidic platforms for various applications. We have treated two different types of paper (paper towel and printing paper) with various treatment methods such as laser printer flattening, fluorocarbon polymer coating, HCl-impregnation, and combination of these methods. We then studied their lyophobicity characteristics by measuring static and dynamic contact angles as well as bouncing experiment. We found that HCl-impregnation is a simple yet powerful method to engineer certain types of papers to make them super-lyophobic substrates against gallium-based liquid metals and effective for more than 30-days after impregnation. To show the feasibility, we demonstrated manipulation of a Galinstan® droplet along microfluidic channels formed on the HCl-impregnated paper.

Ground wood cellulose paper exhibits a practicable cleaning laser fluence window during middle-UV radiation processing. In this case, a minimum dose volume density should be applied. However, cleaning of bleached cellulose paper is accompanied by strong yellowing and destruction. The presence of charcoal graphite particulates shows substantial influence on the yellowing with increasing coverage.

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 .

Lasers have served as cleaning tools for historical objects and artworks for about 40 years. In many cases, superior results of laser cleaning were achieved with respect to traditional methods. In this technique, contaminations on the surface of the object are ablated by laser irradiation. In order to apply laser cleaning method to fragile materials such as paper made of cellulose or parchment, heat deposition to the bulk should be minimal, to prevent damage. In this work, it is demonstrated that laser pulses with femtosecond (fs) duration can exhibit non-thermal ablation of contaminants on paper samples. In particular, laser cleaning studies are concentrated on paper samples with sizing. Fs laser cleaning is performed on artificially soiled and aged samples, as well as on historical ones. The laser used in the experiments has pulse duration of 550 fs and 1030 nm center wavelength. The fluence of the laser is varied and the post-cleaning statuses of samples are investigated. The analyses are color changes, fiber integrity, chemical composition changes and mechanical strengths. These results show that fs lasers can be very efficient in cleaning paper samples, yielding minimal discoloration and no damage to fibers distinguishable on microscopic examination. The presence of sizing also provides further protection against possible side effects.

In the present work, the analytical potential of laser induced breakdown spectroscopy (LIBS) for the discrimination of paper types and prints made by digital printers on these papers was assessed. Six different paper types (including standard office papers, color paper and non-bleached paper), and eight printers (including laser and inkjet, as well as color and black printers) were included in the study. Only one or two laser shots were delivered to each sample in order to cause minimal sample destruction and provide maximum spatial resolution. The statistical evaluation of LIBS spectra was performed by multiple methods including three comparative functions (linear correlation, sum of squared deviations and overlapping integral) as well as two advanced statistical methods (multivariate curve resolution alternating least squares (MCR-ALS) combined with classification tree and discriminant analysis (DA)). The best classification results were obtained with the newly introduced MCR-ALS/DA approach, which proved to be 96.3% accurate in the identification of the paper type and 83.3% accurate in the identification of the printer type, based on the LIBS spectrum collected from just a single laser shot to the sample. It was found that the UV part of the LIBS spectrum can be used most efficiently for the discrimination.

Mode-locked fiber lasers emitting short pulses of light at wavelengths of 2 μm and longer are reviewed. Rare-earth doped silica and fluoride fiber lasers operating in the mode-locked regime in the mid-IR (2–5 μm) have attracted attention due to their usefulness to spectroscopy, nonlinear optics, laser surgery, remote sensing and ranging to name a few. While silica fiber lasers are fundamentally limited to emission wavelengths below 2.2 μm, fluoride fiber lasers can reach to nearly 4 μm. The relative infancy of fluoride fibers as compared to silica fibers means the field has work to do to translate the mode-locking techniques to systems beyond 2 μm. However, with the recent demonstration of a stable, mode-locked 3 μm fiber laser, the possibility of achieving high performance 3 μm class mode-locked fiber lasers looks promising.

A novel and low-cost wall paper single-walled carbon nanotubes (SWCNTs) absorber was fabricated by high viscosity of polyvinyl alcohol (PVA) aqueous solution and vertical evaporation technique. Sandwich structure wall paper SWCNT (SSWA-SWCNT) absorber was constructed by a piece of wall paper SWCNT absorber, a piece of round quartz and an output coupler mirror. We exploited it to realize mode locking operation in a diode-pumped Nd: GdVO 4 laser. A pulse duration of 9.6 ps was produced with an average power of 870 mW. The stable mode locking operation was obtained when the average power is less than 300 mW.

Current methods used in document examinations are not suitable to associate or discriminate between sources of paper and gel inks with a high degree of certainty. Nearly non-destructive, laser-based methods using laser induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to improve the forensic comparisons of gel inks, ballpoint inks and document papers based on similarities in elemental composition. Some of the advantages of these laser-based methods include minimum sample consumption/destruction, high sensitivity, high selectivity and excellent discrimination between samples from different origins. Figures of merit are reported including limits of detection, precision, homogeneity at a micro-scale and linear dynamic range. The variation of the elemental composition in paper was studied within a single sheet, between pages from the same ream, between papers produced by the same plant at different time intervals and between seventeen paper sources produced by ten different plants. The results show that elemental analysis of paper by LIBS and LA-ICP-MS provides excellent discrimination (> 98%) between different sources. Batches manufactured at weekly and monthly intervals in the same mill were also differentiated. The ink of more than 200 black pens was analyzed to determine the variation of the chemical composition of the ink within a single pen, between pens from the same package and between brands of gel inks and ballpoint inks. Homogeneity studies show smaller variation of elemental compositions within a single source than between different sources (i.e. brands and types). It was possible to discriminate between pen markings from different brands and between pen markings from the same brand but different model. Discrimination of ~ 96–99% was achieved for sets that otherwise would remain inseparable by conventional methods. The results show that elemental analysis, using either LA-ICP-MS or LIBS, provides an effective, practical and robust technique for the discrimination of document paper and gel inks with minimum mass removal (9–15 μg) and minimum damage to the document's substrate.

HV transformers are taken into account as the heart of the power distribution system. The on-line monitoring based on the oil analysis offers a rapid diagnostic technique to detect the probable faults. In fact, the transformer malfunctions can be detected using UV laser spectroscopic methods. Here, a novel technique is presented based on simultaneous laser induced fluorescence (LIF) and laser induced breakdown (LIB) spectroscopy for hyper sensitive identification of the oil degradation. Oil is mainly degraded due to the internal transformer faults such as overheating and partial discharge. The spectroscopic characteristics of oil in paper substrate were obtained due to ArF laser irradiation. It was shown that the amplitude of fluorescence signal increases when the oil suffers aging and degradation. A couple of additional characteristic carbon and H α emissions appear in the corresponding breakdown spectra too.

Laser ablation was applied for surface cleaning and spectroscopic diagnostics of historical paper documents and model samples in the framework of the conservation projects. During cleaning the spectra of ablation products were recorded by means of the LIBS technique which allowed for nearly non-destructive identification of surface layers such as contaminants, substrate and pigments. For consecutive laser pulses a strong decrease of band intensities of the emission lines of Ca, Na, K, Al and Fe ascribed to contaminants were observed. The effect was used for monitoring of the cleaning progress of stained paper. For surface cleaning and spectra excitation the Q-switched Nd:YAG laser of 6 ns pulsewidth operating at wavelengths of 266, 355, 532, and 1064 nm and of fluence selected from the range 0.3–0.9 J/cm 2 was applied. The ablation parameters were optimized in agreement with the literature and the results were confirmed by surface studies and testing of the mechanical and chemical properties, and also by the response to the ageing process of the paper substrate. In case of the model paper irradiated in the UV range at 266 and 355 nm a visual inspection revealed local damages of the cellulose fibers accompanied by a decrease of the mechanical strength of the substrate. The effect was more pronounced after artificial ageing. The best results were obtained for samples irradiated at 532 nm and at laser fluence below the damage threshold of 0.6 J/cm 2 , which is in agreement with literature.

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.

A comparison between single- and double-pulse LIBS for the quantitative elemental analysis of used engine oils has been performed. Paper substrates have been utilised for the analysis and are shown to provide better limits of detection (LODs), no splashing and easier sample handling compared to the previously reported experiments using laminar liquid jets and static liquid surfaces. Single-pulse LIBS analysis of oil on paper substrates has had on average 2× better LODs than was obtained using flowing liquid jets, while double-pulse LIBS showed 4× improvement. Single-pulse LIBS has been found preferable for the analysis, as the use of an additional laser in double-pulse LIBS yielded only a minor improvement while adding substantially to the complexity and cost of the system.

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.

Photorefractive interferometers have been employed for the detection of ultrasound in metals and composites since 1991 [1–4]. Instances of laser-generated ultrasound and laser-based detection in paper were reported in 1996 [5]. More recently, bismuth silicon oxide (BSO) photorefractive interferometers were adapted to detect ultrasound in paper [6]. In this article we discuss BSO and GaAs photorefractive detection of ultrasound on different paper grades and present the resulting waveforms. Compared to contact piezoelectric transducer methods, laser interferometry offers signifcant advantages. One of these is that it is a noncontact technique. This is especially important for on-line application to lightweight papers which could be marked or damaged by contact transducers. Broadband ultrasonic laser generation matched with the broadband sensitivity of laser interferometers is another beneft. This is important for obtaining narrow pulses in nondispersive time-of-fight determinations and for measuring the phase velocity of dispersive modes over a wide frequency band. Also, laser ultrasonic techniques provide a measure of bending stiffness through the analysis of low frequency A0 waves.

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.

Material distributions in paper and paper coatings are important factors which determine the characteristics and quality of paper. We have used laser-induced plasma spectroscopy (LIPS) to determine various properties of coated and uncoated papers. Depth profiles of double coated papers were determined. Microscopic variations of pigments in a double-coated paper were analyzed. It was observed, that the two coating layers can be distinguished, if they differ enough in composition. Filler distributions of uncoated copier papers were determined. The surface of the paper was studied for five samples containing different amounts of binder in the coating. Lateral contamination in paper analysis i.e. splash over effect of ablation was studied by varying the sampling distance and number of laser pulses used for ablation. Influence of splash over effect on lateral analysis is briefly discussed.

We argue that recent paper “Radially polarized terahertz radiation in laser-induced linear plasma wake” by Suyun Zhou and Yanfang Li [Optik 127 (2016) 3495–3498] is incorrect. These authors computed THz radiation from a plasma filament produced by a curl-free current. However it has been long known that curl-free current does not radiate.

This paper reports the effects of laser ablation upon multiple-layered coloured inks which have been printed on an ordinary white paper. The aim of this work is to examine the feasibility of generating a fully tactile three-coloured image by selectively removing ink layers to reveal underlying layers of a different colour. In this paper laser ablation has been carried out upon four layered ink samples consisting of white/cyan/white/black layers. Ablation was carried out using a Q-switched Nd : YAG laser. The results show that it is possible to selectively remove the inks to expose both the top white and the cyan layers, although charring occurs with deeper ablation. An evaporation/decomposition mechanism is proposed to describe process of ink ablation.

An experimental study of radiative ignition of sheet paper has been performed in microgravity to determine the events occurring in ignition processes in a quiescent field. Experiments were conducted on filter paper using a CO2 laser with a mean incident flux of about 5.8 W/cm2 in various oxygen concentrations (0%–35%) and at various pressures (0.5–2 atm). The laser beam was irradiated perpendicular to the sample surface. The ignition delay was measured for various experimental conditions with high-speed video images or Hi-8 video images taken in microgravity. The gas-phase and solid-surface temperature changes were observed by a Mach-Zehnder interferometer and an infrared camera. The results showed that the ignition delay became shorter with increases in oxygen concentration, and it was observed that the gas-phase temperature increased more than that of the solid surface. Further, the increase in gas-phase temperature was larger with oxygen than without oxygen, though there were increases in the gas-phase temperature even without oxygen. The results showed that chemical processes, such as gas-phase reactions, are essential in the ignition mechanism, as are physical processes, such as heating the solid material, and gas-phase laser absorption. The research clearly showed the importance of each process by utilizing a non-convective flow field where gravitational forces were not acting.

It is shown that the work entitled “Conversion of Laguerre-Gaussian beams into Gaussian beams of reduced focal spot by use of a circular echelon” repoted by S.Cherif et al. (Optik 127 (2016) 3134–3137), follows the same procedures as presented in the papers of the authors ([A. Hasnaoui, A.Bencheikh and K.ait ameur, Opt. Lasers Eng. 49 (2011) 248–251], [A. Hasnaoui, A. Bencheikh, M. Fromager, E. Cagniot, K. Ait-Ameur, Creation of a sharper focus by using a rectified TEMp0beam, Opt. Commun. 284 (2011) 1331–1334]), but concludes that their results are substantially different from the results of the authors. We find that there is no new result in the whole work, in addition there are big mistakes that we look to clarify and to correct.

The spectra of laser excited surface plasma (LIPS) recorded for historical, originally contaminated paper and also for model samples reveal reach structures which vary strongly for successive excitation pulses. The characteristic bands are ascribed to contaminants (Na I, Ca I) and pigments (e.g. V I, V II, Ti II, Fe I). Results confirm that the applied technique allows for nearly non-destructive identification of the composition of surface layers such as contaminations and pigments.

The propagation velocities of laser-generated ultrasonic plate waves were measured on paper moving at 10 m s −1 using a Mach–Zender interferometer and scanning mirror. Fast- and slow-propagating plate wave vibrational modes were detected. Velocity measurements were made on four types of paper, perpendicular to and in the direction of paper motion. Laser-ultrasonic measurements of phase velocities for the fast-propagating vibrational mode were compared with contact transducer-based measurements. The effect on signal amplitude of (1) distance from the detection point to the ultrasound generation point and (2) the pulse energy of the ultrasound generation laser was studied using stationary paper.

Laser cleaning of delicate biological composite materials such as ancient parchment manuscripts from the 15th and 16th century and printed paper from the 19th century is demonstrated with an ultraviolet excimer pulsed laser at 308 nm. Laser fluence levels must stay below the ablation and destruction threshold of the parchment or paper substrate, and have to surpass the threshold of the contaminant matter. Foreign layers to be removed must exhibit a higher optical density than the artifact substrates. Synthetic carbonaceous dirt modelled by water-soluble black crayons showed a characteristically weak featureless laser-induced plasma spectroscopy spectrum near the noise limit. It turned out that laser-induced plasma spectroscopy is of limited use in monitoring halting points (or etch-stops) because it relies on the destruction not only of the laterally inhomogenously distributed contaminant but also of pigment phases on a microscopically rough parchment substrate. Laser-induced fluorescence spectroscopy, however, promises to be a valuable non-destructive testing technique for etch-stop monitoring.

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.

Experiments have been conducted to study the generation of ultrasonic Lamb waves in copy paper using a pulsed Nd : YAG laser. The signals were detected with an out-of-plane heterodyne Ar+ laser interferometer. The effect of the generation laser spot size, energy density, and total energy on the transfer of energy from the generation laser to the two lowest Lamb wave modes, a0 and s0, was investigated. As with metals excited in the linear thermoelastic regime, the signal energy increases as the square of the input laser energy. However, unlike in metals, significant statistical variations of the waveforms (peak amplitudes, arrival time) were observed and quantified by means of cross-correlation techniques. Also unlike in metals, it appears that there is an optimum spot radius of about 90 ± 20 μm (i.e. an energy density of about 22.4 J/cm2) for efficient generation of both a0 and s0 mode in the copy paper we studied. The shift in frequency content of the Lamb waves was examined as a function of the generation spot size. Damage at the generation spot was assessed by photographic microscopy.

The paper reports on immediate effects of pulsed laser operating at 532 nm and fluences below 2.5 J cm –2 on soiled cellulose. The degree of polymerisation was determined viscometrically, while diffuse reflectance FTIR was used to gain insight into the changes in the chemical composition. Although no detectable immediate changes were observed after treatment of paper with laser beam at 532 nm, the irradiation of paper containing carbonaceous dirt resulted in significant discoloration of the treated substrate. The possible reasons for the extensive formation of yellow chromophores are discussed.

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.

Web speed and draw measurements on an industrial paper machine are generally obtained by means of rotating speeds. It is now possible to measure true linear speed, without contact by several techniques which are briefly reviewed. The principle of speed measurement by correlation of two optical signals is given. An instrument based on the autocorrelation of a single signal laser transducer is described as well as its signal processing specific unit. Results are presented, the main features of the instrument are discussed. Possible applications in the paper industry and on other materials are listed, having in mind process control.

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 the present study, continuous wave fiber laser of 400W capacity with CNC controller is used for the cladding operation. SS316 +WS2+Cr powder mixture is taken as clad materials and SS316 of 5 mm thick plate as substrate materials. A homogeneous powder mixture is pasted over the substrate surface and laser beam is scanned by imparting motion to the XY table to get required cross-section area of the clad surface. By adjusting the (±) z–axis of working table the required size of spot diameter (divergence of laser beam) is obtained. For getting the required scan cross-section area, a CNC programmed was built with the help of SINUMERIK 828D SIEMENS controller. A gas chamber made of perpesx sheet having quartz window with different gas purging facility is used to creating required working environment. The laser beam is passed through a quartz window and strike on the surface of the powder layer. Various input process parameters were consider during the experiment such as laser power: 100-200 W, scanning speed: 500-1000 mm/min, % v/v composition of WS2: 5-15 and % v/v composition of Cr: 10 considered as variable process parameters and laser spot diameter: 0.4 mm, hatching gap: 0.2 mm, powder layer thickness: 0.7 mm. The prepared clad specimens were cut with the help of wire-EDM machine for characterization purpose. Then the sectioned specimens were polished using emery paper of different grit size followed by diamond paste polishing to get mirror finishing. Field emission scanning electron microscope (FESEM) (Model: Supra 55, Make: Zeiss, Germany) was used to study the microstructure and to do the elemental analysis. X- Ray diffraction (XRD) technique was used for phase analysis. The diffraction angle (2θ) was kept in the range of 20°-120° to detect the range of chemical compounds formed during the laser cladding process. From XRD analysis, it is can be observed that different intermetallic compounds were formed during laser cladding operation such as WS2, FeS2, FeS, CrS. The micro-hardness of the sectioned surface was measured along the clad depth using a Vickers micro hardness tester (Model: Economet VH-1 MD, Make: Chennai Metco, India). The dry sliding wear behaviour of the clad samples was analysed using a pin on disk tribometer (Make-DOCUM, India, Model: TR 201LE). The wear tests were conducted at an angular speed of 500 rpm at a radial distance of 60 mm. A dead load of 3kgf was maintained during the test for a period of 10 minutes

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.