Scanning CO2 Laser Research Articles

Reactivity of high active aluminum powder with RDX and HMX mixtures

In order to reveal the interaction law of high active aluminum powder with RDX and HMX mixture, the thermal decomposition behavior of highly active Al powder and its interaction with typical nitramine explosive RDX and HMX were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), thermo-mass spectrometry (TG-DTG-DSC-MS) and CO2 laser ignition technology. Results show that when the nanometer aluminum powder and RDX and HMX respectively, two typical nitramine explosive mixing action is of little influence on the mixing action to respond to the thermal decomposition of HMX, depress RDX points liberation degree of temperature, both the thermal decomposition process of mixed system for random nucleation and subsequent growth process, the ignition delay time decreases with the increase of laser ignition power density. The ignition delay time and ignition energy of the mixture of high active aluminum powder and RDX are greater than that of the mixture of high active aluminum powder and HMX and the high active aluminum powder.

Evolution Regularity of Continuous Surface Structures Shaped by Laser-Supported Fictive-Temperature Modifying

The influence of residual heat on the fictive temperature modification zone of fused silica for different CO2 laser scanning time intervals was investigated to precisely control the profiles of hydrofluoric (HF) acid-etched fused silica surface, which were formed by the increasing HF acid-etching rate for fused silica with increasing fictive temperature induced by CO2 laser scanning. The surface profiles of HF acid-etched fused silica treated by different scanning time intervals of CO2 laser were measured by a stylus profilometry, and experimental results indicate that the CO2 laser scanning time intervals intensively influence the HF acid-etched surface profiles of fused silica. The increasing depth of surface profiles treated by shorter scanning time intervals shows that the fictive temperature modification zone significantly expands. Numerical simulations of the fictive temperature modification zone induced by different scanning time intervals indicate that the residual heat of CO2 laser scanning with shorter time intervals leads to a dramatical increase in the fictive temperature modification zone. By adjusting the residual heat of CO2 laser scanning intervals, various surface profiles of fused silica can be obtained by HF acid-etching of fused silica.

Laser-Sculptured Hierarchical Spinous Structures for Ultra-High-Sensitivity Iontronic Sensors with a Broad Operation Range.

Tactile pressure sensing over a wide operation range (>1 MPa) is challenging for a variety of applications in fields such as aviation, oceanography, and biomedicine. Recently, innovative strategies have been utilized to improve the performances of tactile sensors using specially designed structures, dielectric layers, and electrodes. Here, a hierarchical structural design based on ionic gel films has been utilized to build iontronic pressure sensors with ultrahigh sensitivities and broad operation ranges. Sculptured patterns made by a controlled CO2 laser scanning process have been produced on polyimide films to achieve two kinds of protrusion structures for high specific surface areas and strength to withstand high pressure. The iontronic sensor has been constructed by adding two screen-printed electrodes of high surface areas to achieve an ultrahigh sensitivity of 2593 kPa-1 and a wide pressure range from 0 Pa to 3.36 MPa. The prototype device also has a fast response and recovery time of 26 and 13 ms, respectively, and an excellent mechanical durability in the endurance test of over 2700 repeated loading and unloading cycles under a pressure of 1 MPa. Several application examples have been demonstrated, including the detection of physiological signals on human volunteers, the feedback control of intelligent robots, the grasping operation of underwater soft grippers, and the environmental wind-speed monitoring. As such, this work demonstrates a versatile and economical methodology to produce high-performance flexible sensors for various potential applications.

Raman suppression in 5 kW fiber amplifier using long period fiber grating fabricated by CO2 laser

Long period fiber grating (LPFG) can be used as a band rejection component, providing a potential effective way for Stimulated Raman scattering (SRS) suppression in high power fiber laser. Here, an improved CO2 laser scanning system with a galvanometer is built up for fabrication of LPFGs, which greatly improves the speed and consistency of grating inscribing. The characteristics of the manufactured LPFG is measured in detail, then a direct laser diode pumped 5 kW-level fiber amplifier system is established to test the validity of the LPFGs for Raman suppression for the first time. Experimental results show that the SRS suppression ratio is about 14 dB at 5.1 kW with the LPFG being inserted between the seed and the amplifier stage, meanwhile the effective output signal laser power is increased. In contrast to the ultraviolet laser exposed band rejection components, such as chirped and tilted fiber Bragg grating (CTFBGs), this type of LPFG does not need photosensitive fibers, annealing treatment and has a much lower thermal effect, which is very useful for high-power fiber lasers applications.

3D-Printing of Proton Conducting Ceramics

3D-printing technology is being extensively utilized in energy sector, as it allows for manufacturing complex structures (compacted stacks, desired microarchitectures and porosity) and customizable shapes for specific devices. Moreover, fast prototyping time and reduction of production cost make this technology promising for industrial applications. Up to now, plenty of 3D-printed energy conversion and storage devices and hence precursor materials have been proposed. Reported examples concern solar cells, biofuel cells, rechargeable ion batteries, carbon-based supercapacitors and others [1-2]. On the other hand, 3D-printing of proton-conducting materials is rarely reported. The pioneering research was presented by Mu et al., who have developed novel laser 3D-printing method which allows to obtain protonic ceramics with the desired crystal structures, microstructures, and geometries [3]. The method consists of the preparation of printable paste from component raw materials (carbonate and single metal oxides) mixed with sintering aid, the deposition of a thin green film of the targeted protonic ceramics, and the reactive sintering by rapid CO2 laser scanning. Such method was successfully applied for the synthesis of dense electrolytes (e.g. BCZYYb, BZY20), porous electrodes (e.g. BCZYYb+NiO, BaCo0.4Fe0.4Zr0.1Y0.1O3-δ), dense interconnect (La0.7Sr0.3CrO3-δ/LSC), and dense mixed protonic and electronic-conduction composite (BaCe0.85Fe0.15O3-δ– BaCe0.15Fe0.85O3-δ/BCF) [4]. The second available example is devoted to the 3D-printed proton exchange membrane and has been recently reported by K. Iwase and co-workers [5]. Scientists developed UV-cured ink (mixture of proton-conducting ionic liquids, inorganic silica nanoparticles, and UV-sensitive photocurable resins) which can be successfully applied to the printing of proton exchange membranes.In the present study, we developed 3D-printing of protonic ceramics- Ba0.5La0.5Co1-xFexO3-δ (0 ≤x≤ 1), which are promising materials for positrodes in protonic ceramic fuel cells [6]. The Project is devoted both to the construction of 3D-printer and ink preparation. Two printing technology- fused deposition modeling and extrusion-based 3D-printing were selected and embedded into one 3D-printer. In addition, the system was equipped with IR laser for post-processing. Ink (solid filament or gel) was prepared from ceramic powder and polymer (i.e. polylactic acid or polyvinyl alcohol), which act as a matrix and is removed at the end. Various compositions (e.g.ceramic to polymer ratio, polymer concentration, solvent) and synthesis conditions (e.g. time, temperature) were tested. A lot of attention was paid to the proper ceramic dispersion, which ensures printouts homogeneity. Therefore, various approaches such as ball-milling of ceramic and ultrasonication of gel were optimized and implemented. The last important step was devoted to the laser post-processing, during which polymer is removed and ceramic is sintered. Various laser powers, scan speeds and number of scans were tested. Printed layers before and after post-processing were characterized by X-Ray diffraction, Fourier Transform Infra-Red spectroscopy and Scanning Electron Microscopy. In the future it is planned to adopt developed technology and use it for the printing of multi-layered positrodes with graded functionality.

Strain-Insensitive Simultaneous Measurement of Bending and Temperature Using Long-Period Fiber Grating Inscribed on Double-Clad Fiber with CO₂ Laser.

Here we report an optical fiber sensor capable of performing strain-insensitive simultaneous measurement of bending and temperature using a long-period fiber grating (LPFG) inscribed on doubleclad fiber (DCF) with a CO₂ laser at ˜10.6 μm. The LPFG inscribed on DCF, referred to as a DC-LPFG, was fabricated by scanning CO₂ laser pulses on an unjacketed DCF with a specific period. Due to co-directional mode coupling, the fabricated DC-LPFG has discrete attenuation bands widely distributed over hundreds of nanometers. Among these wavelength-dependent loss dips, adjacent two dips with different resonance wavelengths were selected as sensor indicators for the measurement of bending and temperature. For these two indicator dips designated as dips A and B, their bending and temperature responses were investigated in a curvature range of 4.90 to 21.91 m-1 and a temperature range of 30 to 110 °C. With increasing bending applied to the DC-LPFG at room temperature, dips A and B showed different blue shifts. The bending sensitivities of dips A and B were measured to be approximately -0.77 and 0.51 nm/m-1, respectively. Unlike the bending response, they showed red shifts of different amounts with increasing ambient temperature, while the sensor head (i.e., the DC-LPFG) remained straight without any applied bending. The temperature sensitivities of dips A and B were measured to be ˜0.094 and ˜0.078 nm/°C, respectively. Owing to their linear and independent responses to bending and temperature, bending and temperature changes applied to the DC-LPFG could be simultaneously estimated from the measured wavelength shifts of the two indicator dips using their pre-determined bending and temperature sensitivities. Moreover, in a strain range of 0 to 2200 με (step: 200 με), strain-induced spectral variations of dips A and B were also measured, and the strain sensitivities of dips A and B were evaluated as approximately -0.028 and -0.013 pm/με, respectively. These strain-induced wavelength shifts were so small that they had little effect on the measurement results of bending and temperature. Thus, it is concluded that the fabricated DC-LPFG can be employed as a cost-effective sensor head for strain-insensitive separate measurement of bending and temperature.

Ultrasonic doping and photo-reduction of graphene oxide films for flexible and high-performance electrothermal heaters

Thermotherapy has emerged as one of the most promising treatments for arthritis, a prevalent, crippling, painful bone disease. This demands more flexibility, energy-efficiency, safety, and light-weight in thermotherapy packs and hot clothing. Heteroatom doping is a metal-free, cost-effective way to improve carrier concentration and hence electrical and thermal conductivity in reduced Graphene Oxide (rGO) thus rendering it suitable for wearable joule heaters. However, the current doping techniques result in complex chemical structures that hinder phonon propagation and suffer other problems such as low yield, low scalability, and rigidity of the final product. Here, we disclose a novel and facile, low-temperature technique for nitrogen doping and photoreduction of graphene oxide (GO) films for high-performance, flexible graphene-based electrothermal heaters. The nitrogen atoms are introduced into the GO lattice with the aid of ultrasonic power in a wet chemical doping phase and maskless, automated, rapid CO2 laser scanning is used for the concurrent removal of oxygen-containing functional groups and the rearrangement of nitrogen atoms in the graphene lattice. X-ray Photoelectron Spectroscopy (XPS) studies reveal up to 5.43% nitrogen dopant concentration with a high carbon to oxygen ratio of 16, while Raman studies uniquely show improved atomic ordering with ID/IG ratio of 0.51 in the nitrogen-doped Laser reduced graphene oxide (N-LrGO) films. The fabricated N-LrGO heater has a sheet resistance of 26 O/sq. and attains a higher steady-state temperature of up to 245.7 °C at a low driving voltage of 9 V with a low power demand of 0.7 Wcm−2 and a heating rate of 103 °C/s. Its excellent temperature distribution and high flexibility join with the scalability of the preparation technique to demonstrate great potential for its incorporation with next-generation wearable electronics powered by low voltage portable energy storage devices.

In vivo spectral guided removal of composite from tooth surfaces with a CO2 laser.

Dental composites are used as restorative materials to replace tooth structure after the removal of caries, shaping, covering teeth for esthetic purposes and as adhesives. Dentists spend more time replacing existing restorations that fail than they do placing new restorations. Tooth colored restorations are difficult to differentiate from the surrounding tooth structure making them challenging to remove completely without incidental removal of healthy tooth structure. Previous studies have demonstrated that CO2 lasers in conjunction with spectral feedback can be used to selectively remove composite from tooth surfaces. In addition, we assembled a system feasible for clinical use that incorporates a spectral feedback system, scanning system, articulating arm and a clinical handpiece and subsequently evaluated the performance of that system on extracted teeth. The purpose of this study was to test this system in vivo to demonstrate its efficacy relative to dental clinicians. Eight test subjects with premolar teeth scheduled for extraction for orthodontic reasons had bilateral premolars prepared with small occlusal cavity preparations and filled with dental composite. The laser scanning system was used to remove the composite from one of the preparations and a dental handpiece was used to remove the composite from the other. Cross polarization optical coherence tomography was used to measure the volume of the preparation before and after composite placement and removal. There was no significant difference in the loss of enamel and residual composite between the laser and the handpiece. This study demonstrated that a computer controlled spectral guided CO2 laser scanning system can be used in vivo to selectively remove composite from tooth surfaces.

Single Crystal Ge Core Fiber Produced via Pressure Assisted Melt Filling and CO2 Laser Crystallization

We present a simple two step process for the fabrication of single crystal germanium core fibers. Germanium is deposited into a capillary in a highly polycrystalline state using the pressure assisted melt filling technique. This core material is then melted and recrystallized in single crystal form using a scanning CO2 laser process. This combination of techniques is an efficient means of producing fibers of practical lengths and core sizes for optical and optoelectronic devices. We produce small core fibers of $\mathrm {1~ \mu \text {m} }$ radii and lengths in the centimeter regime. It is anticipated that this process can be optimized so that sub-micron cores can be produced to create fibers that have single-mode operation.

Torsion bidirectional sensor based on tilted-arc long-period fiber grating.

Fiber torsion sensor has been researched for many years due to its various structure and sensitive response. In order to distinguish the torsion direction, fiber sensor still faces some difficult problems, including complex fabricating condition, special fiber structure and limited sensitivity. In this paper, a novel long-period fiber grating (LPFG) formed by tilted-arc grids is designed and fabricated in the normal simple-mode fiber, showing small size and high sensitivity. The asymmetrical tilted-arc grid structure can induce considerable chirality into the tilted-arc LPFG to enable it to distinguish torsion direction, which doesn't need any equipment to rotate or twist the fiber in the fabrication process. Theoretical analysis indicates that the structure can respond opposite wavelength shifting to the opposite torsion directions, and the torsion sensitivity is related to both the radius and tilted angle of grid. A series of tilted-arc LPFGs are fabricated with CO2-laser scanning and tested in torsion experiment, all of whom can distinguish bidirectional torsion. The maximum sensitivity value can reach 0.514 nm/(rad·m-1), which is higher than many normal tilted LPFGs and twisted fiber structures. The novel LPFG has the potential to be applied in directional torsion field due to its direction-distinguishing ability, high sensitivity and simple fabrication.

High precision laser ablation of fused silica using pulsed CO<sub>2</sub> laser

Laser polishing is a novel processing method which can achieve a super-smooth surface of an optical component. However, there are residual ripples and surface distortions after laser polishing. High precision laser ablation can be used to correct the residual ripple and shape of the component, making it a promising figuring method. In this paper, the experiment of high precision laser ablation of fused silica was carried out with pulsed CO2 laser. It is verified that high-precision uniform ablation in a local region can be achieved by controlling the laser overlap rate, and different nanometer ablation depths can be obtained by controlling the laser power density. However, it has been found that there is thermal accumulation and over-ablation during the laser ablation process. A three-dimensional numerical model was established to simulate the process of pulsed CO2 laser scanning on a fused silica surface. The surface temperature distribution and evolution of fused silica with different overlap rates and pulse repetition frequencies were analyzed. The numerical results show that the increase of the overlap rate could lead to over-ablation. With a suitable overlap rate, the high pulse repetition frequency could result in significant heat accumulation.

Laser surface modification of structural glass for anti-slip applications

The use of soda-lime silicate glass as a structural element has become frequent in modern buildings. The load-bearing applications of glass in floors, footbridges, terraces, or stairs require an optimal combination of non-slippery properties of the surface, element weight, and strength, and structural glazing can be compromised by the incorporation of laser surface patterned ornamental motifs. Laser surface modification has significant advantages for selective surface area modification; nevertheless, the mechanical performance of the processed glass remains unknown, which precludes reliable structural calculations and employment in construction. In this study, we investigated the surface modification of annealed and heat-strengthened glass via CO2 laser scanning for the production of rough anti-slip surfaces. The surface roughness and the reduction of the bearing load strength were quantified. Slip resistance-enhanced surfaces with roughness values (Rz) above 20 μm and characteristic bending strength preservation up to 74% were obtained. The results pave the way for the use of laser surface-modified plates in laminated glass elements with optimized strength calculation and weight reduction.

Effect of Laser-derived Surface Re-melting of YSZ Electrolyte on Performance of Solid Oxide Fuel Cells

A simple and effective technique to reduce the overall fuel cell polarization resistance was introduced on a conventionally sintered YSZ electrolyte by creating a hybrid microstructure using low-intensity CO2 laser scanning methods. After laser modification of the YSZ electrolyte surface on the cathode side, the overall polarization resistance was reduced from 513 to 124 Ω cm2, and the maximum power density was increased by 28% from 1.86 to 2.38 mW/cm2 at 450 °C. This improvement was due to the enhanced surface kinetics by higher grain boundary density on the YSZ surface from recrystallization after laser scanning.

Laser-Induced Graphene on Additive Manufacturing Parts.

Additive manufacturing (AM) has become more prominent in leading industries. Recently, there have been intense efforts to achieve a fully functional 3D structural electronic device by integrating conductive structures into AM parts. Here, we introduce a simple approach to creating a conductive layer on a polymer AM part by CO2 laser processing. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy were employed to analyze laser-induced modifications in surface morphology and surface chemistry. The results suggest that conductive porous graphene was obtained from the AM-produced carbon precursor after the CO2 laser scanning. At a laser power of 4.5 W, the lowest sheet resistance of 15.9 Ω/sq was obtained, indicating the excellent electrical conductivity of the laser-induced graphene (LIG). The conductive graphene on the AM parts could serve as an electrical interconnection and shows a potential for the manufacturing of electronics components. An interdigital electrode capacitor was written on the AM parts to demonstrate the capability of LIG. Cyclic voltammetry, galvanostatic charge-discharge, and cyclability testing demonstrated good electrochemical performance of the LIG capacitor. These findings may create opportunities for the integration of laser direct writing electronic and additive manufacturing.

Active thermographic inspection of carbon fiber reinforced plastic laminates using laser scanning heating

In this study, inspection capability of active thermographic nondestructive inspection using the laser scanning method was examined. Carbon fiber reinforced plastic (CFRP) specimens were heated using a CO2 laser scanning device and their inspection capability was investigated. The experimental results indicate that the temperature and phase behavior after laser scanning heating were similar to those after conventional instantaneous flash heating. We also investigated the effect of the relationship between the scanning direction and fiber direction of the tested CFRPs on defect detection. The numerical and experimental results showed that the observed temperature contrast appearing on the defective surface varied depending on the scanning direction, and the temperature contrast increased when the scanning direction was the same as the fiber direction of the laminates. In addition, it was found that defects in a CFRP specimen located 10 m from the heat source could be detected using the laser scanning heating. These results suggest that using the laser scanning heating method is effective to inspect large objects located at far distances.

Sustainable Fabrication of Glass Nanostructures Using Infrared Transparent Mold Assisted by CO2 Laser Scanning Irradiation

Abstract Direct thermal imprinting of nanostructures on glass substrates is reliable when manufacturing net-shaped glass devices with various surface functions. However, several problems are recognized, including a long thermal cycle, tedious optimization, difficulties in ensuring high level replication fidelity, and unnecessary thermal deformation of the glass substrate. Here, we describe a more sustainable and energy efficient method for direct thermal imprinting of nanostructures onto glass substrates; we use silicon mold transparent to infrared between 2.5 and 25 μm in wavelength combined with CO2 laser scanning irradiation. The glass strongly absorbed the 10.6 μm wavelength irradiation, triggering substantial heating of a thin layer on the glass surface, which significantly enhanced the filling of pressed glass material into nanostructured silicon mold cavities. For comparison, we conducted conventional direct glass thermal imprinting experiments, further emphasizing the advantages of our new method, which outperformed conventional methods. The thermal mass cycle was shorter and the imprint pattern quality and yield, higher. Our method is sustainable, allowing more rapid scalable fabrication of glass nanostructures using less energy without sacrificing the quality and productivity of the fabricated devices.

CO2 laser-induced weakening in chemically strengthened glass: Improvement in processability and its visualization by Raman mapping

Chemically strengthened glass has become essential in our daily lives and the demand is rapidly increasing in a variety of fields. However, the conventional cutting process is not applicable because of its tough layer with the compressive stress. To achieve higher-throughput production of the glass, we report spatially selective weakening of the compression layer by CO2 laser scanning and provide its visualization by Raman mapping. We demonstrate cutting the scanned glass without shattering using a typical scribing wheel. Finally, we discuss the improvement in processability from the viewpoint of microscopic structures by means of thermal analysis and Raman spectroscopy.

Swirling Gas Jet-Assisted Laser Trepanning for a Galvanometer-Scanned CO2 Laser

Laser-drilled hole arrays are part of an important field that aim to improve efficiency without affecting the quality of laser-drilled holes. In this paper, a swirling gas jet was implemented to assist with laser trepanning for a galvanometer scanned CO2 laser. The proposed swirling gas jet is based on laser trepanning. This swirling gas jet nozzle was composed of four inlet tubes to produce the flow of the vortex. Then, the plume particles were excluded, and spatter on the surface of the workpiece decreased. Thus, this approach can mitigate the problem of overcooling. This study manipulated the appropriate parameter settings, which were simulated by computational fluid dynamics software ANSYS CFX. The proposed swirling gas jet can be used with galvanometer-based scanner systems to keep the laser beam from interference by spatter. In addition, a hollow position of the vortex was achieved by using the four inlet tubes, which resulted in pressure asymmetry in the nozzle and velocity distribution on the surface of the workpiece. The experiment verified that the depth of processing could be enhanced by 110% when trepanning at a scanning speed of 30 mm/s, and that the removal of volume could be enhanced by 71% in trepanning at a diameter of 1 mm by using a swirl assistant compared with a non-assisted condition. Furthermore, the material removal rate of the swirling jet increases when the machining area of the galvanometer-based scanner is larger.

High Sensitivity Chiral Long-Period Grating Sensors Written in the Twisted Fiber

A chiral long-period grating (CLPG) was fabricated successfully by scanning CO2 laser in a twisted conventional single-mode fiber. The strong mode coupling can be achieved in a short grating length. The sensing characteristics of the CLPGs were investigated experimentally. Compared with the conventional long-period fiber gratings, the CLPGs were found to have the similar temperature and refractive index sensitivities and much higher torsion, bending, and strain sensitivities. The high sensitivity of the CLPG can be attributed to the screw-type waveguide structure induced by the scanning laser in the twisted fiber. The proposed CLPGs could have great potential applications as filters and optical sensors.

遠隔加熱装置を利用した構造物のアクティブサーモグラフィ検査システムの開発

This study focuses on active thermographic non-destructive testing using remote heating equipments. Inspection capability using two different heating systems were examined, one is halogen lamp with light collecting mirror and another is CO2 laser scanning system. Experimental results showed that defect in a concrete specimen located at 20-m distance from heater was detected by using the focused halogen lamp, and that defects in a CFRP specimen were detected in thermal images obtained after laser scanning heating. These results imply that inspection system with these heating equipments is effective to inspect objects located far from observers.