Heat conduction analysis of laser CFRP processing with IR and UV laser light

To investigate carbon fiber reinforced plastic (CFRP) composite processing, cutting experiments are performed using a Nd:YAG laser. Both ultraviolet (λ = 266 nm) and infrared (λ = 1064 nm) lights are examined to optimize the laser conditions for cutting CFRP. The experimental data are compared to the results calculated by heat conduction models. The good agreement between the experimental and calculated results indicates that the cutting quality depends on the wavelength of the cutting laser.     

Defect detection in CFRP by infrared thermography with CO2 Laser excitation compared to conventional lock-in infrared thermography

This paper presents a NDT by a CO₂ Laser infrared thermography applied to defect detection in CFRP. The CO₂ Laser is an infrared laser with the wavelength of 10.6 μm. This excitation has a controllable heating beam by a geometric relation D = 0.01575·d, which allows to heat the samples at a specific position (placed at the distance “d”) and area (of a diameter “D”). The PPT interpretation principle was used to reduce the non-uniformity’s effect of the excitation causing inhomogeneous heat. The test with this excitation is much faster than the tests with conventional lock-in thermography method.     

Characterization of diamond thin films deposited by a CO2 laser-assisted combustion-flame method

Diamond thin films were deposited by a CO₂ laser-assisted O₂/C₂H₂/C₂H₄ combustion-flame process. The effect of the deposition parameters, in particular the laser wavelength and power, on the film surface morphology, microstructure and phases present was the primary focus of the work. The laser power was set at 100, 400 and 800 W while the wavelength was varied and set at 10.591 µm in the untuned condition and set at 10.532 µm to resonantly match the CH₂-wagging vibrational mode of the C₂H₄ molecule when in the tuned condition. When the laser was coupled to the combustion flame during deposition the diamond film growth was enhanced as the lateral grain size increased from 1 µm to greater than 5 µm. The greatest increase in grain size occurred when the wavelength was in the tuned condition. Scanning transmission electron microscopy images from focused-ion beam cross-sectioned samples revealed a sub-layer of smaller grains less than 1 µm in size near the substrate surface at the lower laser powers and untuned wavelength. X-ray diffraction results showed a more intense Diamond (111) peak as the laser power increased from 100 to 800 W for the films deposited with the tuned laser wavelength. Micro-Raman spectra showed a diamond peak nearly twice as intense from the films with the tuned laser wavelength.     

Recent developments in garnet based solid state electrolytes for thin film batteries

This paper reviews the current status of, and new progress in, the field of solid state electrolytes (SSE) for lithium ion batteries. In addition to a review of current technologies, we are also presenting our novel results on pulsed laser processing of garnet based SSEs, specifically Li₇La₃Zr₂O₁₂ (LLZO). LLZO powders with a tetragonal structure were prepared by a sol–gel technique, then a pulsed laser annealing process was employed to covert the powders to cubic LLZO without any loss of lithium. The tetragonal LLZO exhibited a Li ion conductivity of 1.8 × 10⁻⁷ S/cm, whereas the laser annealed cubic LLZO showed a Li ion conductivity of 1.0×10⁻⁴ S/cm at room temperature. A systematic study of the effect of pulsed laser annealing (PLA) on the crystal structure, morphology, composition, and ionic conductivity of LLZO was performed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) measurements. These results demonstrate that PLA is a powerful processing technique for synthesizing the high ionic conductivity cubic phase of LLZO at relatively low temperatures, as compared to conventional methods.     

Improving the hot corrosion resistance of plasma sprayed ceria–yttria stabilized zirconia thermal barrier coatings by laser surface treatment

Ceria–yttria stabilized zirconia (CYSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying on NiCoCrAlY-coated Inconel 738LC substrates. After that, the surface of plasma sprayed CYSZ TBCs were glazed using a pulsed Nd:YAG laser. The effects of laser glazing on hot corrosion resistance of the coatings were evaluated in presence of 45 wt%Na₂SO₄ + 55 wt%V₂O₅ corrosive molten salt at 1000 °C. The results revealed that the hot corrosion resistance of plasma sprayed CYSZ TBCs were enhanced more than twofold by laser surface glazing due to reducing specific reactive area of the dense glazed surface layer and consequently, decreasing the reaction between molten salt and zirconia stabilizers.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Laser stimulated piezoelectricity in Er3+ doped GeO2–Bi2O3 glasses containing silicon nanocrystals

We report the first observation of the laser stimulated piezoelectricity in Er³⁺ doped GeO₂–Bi₂O₃ glasses containing silicon nanocrystals, prepared using the simple well known melt quenching technique. Two split beams originated from the same nanosecond lasers were used for the performance of the bicolor laser treatment.The fundamental (λ = 1064 nm) and the doubled frequency (λ = 532 nm) signal of a pulsed nanosecond Nd:YAG laser, as the fundamental (λ = 1540 nm) and the doubled frequency (λ = 770 nm) signal of an Er:glass laser were used.The ratio of power densities between the fundamental and the doubled frequency beams has been varied from 4:1 to 8:1. This value was chosen to achieve the maximum output photoinduced piezoelectric response. The present photoinduced piezoelectricity effect opens a new road for obtaining optically operated piezoelectric devices in germanate composites doped with rare-earth ions.     

Structural and optical properties of neodymium-doped lutetium fluoride thin films grown by pulsed laser deposition

Neodymium-doped lutetium fluoride (Nd³⁺:LuF₃) thin films were successfully grown on MgF₂ (0 0 1) substrates by pulsed laser deposition (PLD). It is void of cracks that are otherwise prevalent due to structural phase transitions in Nd³⁺:LuF₃ during thin film deposition and bulk crystal growth. Cathodoluminescence (CL) spectra revealed multiple emission peaks, with a dominant peak in the vacuum ultraviolet (VUV) region at 179 nm. This peak has a decay time of 6.7 ns. The ability to grow high quality Nd³⁺-doped fluoride thin films would enable fabrication of VUV light-emitting devices that will enhance applications requiring efficient VUV light sources.     

Laser-assisted vibrational control of precursor molecules in diamond synthesis

Control of chemical reactions is the essence of chemistry, producing designed outcomes while suppressing unwanted side products. Laser-assisted molecular vibrational control has been demonstrated to be a potential approach to influencing the outcome of a chemical reaction. In this article, we reviewed recent progress in the laser control of diamond synthesis through vibrational excitation of precursor molecules in a laser-assisted combustion chemical vapor deposition process. Significantly promoted diamond deposition rate (139 μm/h) and crystalline quality were achieved by resonantly exciting the Q-branch (ΔJ = 0) of the CH₂-wagging mode (v₇ mode 949.3 cm⁻¹) of C₂H₄ molecules. Resonant excitation of the fundamental vibrational modes is more effective in promoting diamond growth than random vibrational excitation. Control of diamond crystallographic orientation was also realized by resonantly exciting the R branch (ΔJ = 1) of the CH₂-wagging mode of C₂H₄ molecules and resulted in the preferential growth of {1 0 0}-oriented diamond crystals. Nitrogen-doped diamond films with a nitrogen concentration of 1.5 × 10²⁰ atoms/cm³ were synthesized by resonantly exciting the rotational–vibrational transition (J = 5 → J′ = 6, K = 0) of the N–H wagging mode (v₂ mode) in ammonia molecules. The findings demonstrate the feasibility of laser-assisted vibrational control in steering chemical reactions and controlling reaction outcomes.     

Performance of reinforced concrete slabs strengthened with different types and configurations of CFRP

A total of eight reinforced concrete slabs, 2440 × 600 × 125 mm strengthened with different layers and configurations of CFRP sheets were fabricated and tested. In addition, nonlinear finite element analysis (NLFEA) using ANSYS package was used to simulate the behavior of the test specimens. After reasonable validation of NLFEA with the experimental test results of companion slabs, NLFEA was expanded to provide a parametric study of eighteen slabs. The load–deflection, load strain, and failure modes obtained from the experimental test results and the NLFEA evidently confirmed that strengthening of under-reinforced concrete slabs with CFRP improves the flexural strength capacity and reduce the ductility. This was observed for both types of CFRP. The increase in the flexural strength and the reduction in the ductility increased with the increase in the number of CFRP layers. It was concluded that CFRP strengthening of slabs could be categorized as effective, economical, and successful only if substantial increase in the flexural strength capacity is achieved without changing the failure mode to a shear failure mode at the face of the supports or to a compression failure mode. Comparison between the two CFRP types, for almost equivalent applied area of CFRP, showed that the type of CFRP has significant influence on the behavior of the strengthened slabs. The difference is attributed to the difference in the mechanical properties and the bonding quality of the CFRP material.     

Biomolecular urease thin films grown by laser techniques for blood diagnostic applications

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for bio-sensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (λ = 248 nm, τ_FWHM ? 30 ns, ν = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm². Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Determining fracture toughness from cutting tests on polymers

A cutting test method has been developed for polymers and analysis schemes derived for the determination of the fracture toughness, G_c from the cutting data. The experimental scheme requires the measurement of forces for a cut of width b, in both the cutting direction, F_c/b and the transverse direction, F_t/b. Depths of cut were varied from 0.025 mm to 0.25 mm and the tool rake angle was varied from ?20° to 30°. Cutting was performed at a speed of 10 mm s^?1 on three polymers (HIPS, PA 4/6 and LLDPE). In addition, values of fracture toughness and yield strength were determined for the polymers using standard tests for comparison with the values obtained from cutting. Three analysis methods were derived to analyse the cutting data with the most favoured scheme based on an energy balance and using Merchant’s force minimisation criterion to determine the shear plane angle. This avoids the need to measure the cut chip thickness. Results for HIPS and PA 4/6 gave values of G_c in good agreement with the values determined via LEFM. However, the cutting method is intended for materials such as LLDPE which has a low yield stress and moderately high toughness, i.e. materials which cannot be tested using standard LEFM fracture mechanics tests. The cutting analysis appeared to give valid values of G_c for LLDPE in that they were independent of rake angle. There were some complications when analysing this polymer due to visco-elastic recovery effects in the chip and these have been considered. Finally, the cutting analyses always determined high values of yield stress which would appear to indicate work hardening.     

Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites

Yttria-neodymia double stabilized ZrO₂-based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 °C range. The Y₂O₃ stabilizer content was fixed at 1 mol% whereas the Nd₂O₃ co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 °C was assessed.The nanocomposites with 1–1.75 mol% Nd₂O₃, PECS at 1400 or 1450 °C, have an excellent fracture toughness of 8 MPa m^1/2, although the grain size of both ZrO₂ and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10^?5 Ω m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO₂-based composites with the same overall stabilizer content.     

Optical nonlinearities of BaTiO3 matrix-embedded Au nanoparticles

Composite thin films Au/BaTiO₃ comprising nanometer-sized gold particles embedded in BaTiO₃ matrices were synthesized on MgO(1 0 0) substrates by co-depositing Au and BaTiO₃ targets using pulsed laser deposition technique. The nanostructure of the films and the size distributions of the Au particles were analyzed by high-resolution transmission electron microscopy. Crystal lattice fringes from the Au nanocrystals and BaTiO₃ matrices were observed. The nonlinear optical properties of the Au/BaTiO₃ films were measured using z-scan method at the wavelength of 532 nm with a laser duration of 10 ns. The nonlinear refractive index n₂ and the nonlinear absorption coefficient β were determined to be 2.72 × 10⁻⁶ esu and −1.1 × l0⁻⁶ m/W, respectively.     

Investigation of CFRP laser milling using a 30 W Q-switched Yb:YAG fiber laser: Effect of process parameters on removal mechanisms and HAZ formation

A study on laser machining of Carbon Fibre Reinforced Polymer (CFRP) is presented. Experimental tests were carried out on a 4 mm thick CFRP sheet, using a Q-switched 30 W Yb:YAG fiber laser. The aim of the paper is to detect which process parameters and how they affect the laser beam–material interaction, and to explain the effect of the process parameters on the removal mechanisms and HAZ formation. The process parameters examined were: the laser beam scan speed, the pulse frequency, the number of repetitions of the geometric pattern, the distance between two consecutive scan lines and the scanning strategy. The ANalysis Of VAriance (ANOVA) was applied to a two-level factorial design, specifically developed for this aim. Experimental results showed the presence of different interaction mechanisms such as: ablation, matrix burning and mechanical effect. The damage mechanisms and the influence of the process parameters on the HAZ extent are discussed too.     

Phase transition and microstructure evolution during the carbothermal preparation of Ti(C,N) powders in an open system

Phase transition and microstructure evolution during carbothermal reduction–nitridation of TiO₂ in an open system were investigated using XRD, TGA, SEM and laser particle analysis device. The results show that, the phase evolution sequences are: TiO₂ (anatase) → TiO₂(rutile) → Ti_nO_2n-1(n ? 4) → Ti₃O₅ → Ti(N,O) → Ti(C,N,O) → Ti(C,N). In the reaction process, the predominant reaction mechanism is TiO₂/C solid–solid reaction in the beginning and subsequent the gas–solid reactions mainly between oxides and CO, C and CO₂. The synthesizing powders gradually become finer in form of uniform spherical particles with the formation of cubic phase.     

Monocrystalline silicon surface passivation by Al2O3/porous silicon combined treatment

In this paper, we report on the effect of Al₂O₃/porous silicon combined treatment on the surface passivation of monocrystalline silicon (c-Si). Al₂O₃ films with a thickness of 5, 20 and 80 nm are deposited by pulsed laser deposition (PLD). It was demonstrated that Al₂O₃ coating is a very interesting low temperature solution for surface passivation. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 2 μs to 7 μs at a minority carrier density (Δn) of 1 × 10¹⁵ cm^?3 and the reflectivity reduce from 28% to about 7% after Al₂O₃/PS coating.     

Two-photon absorption of Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single crystalline alloys and their nanocrystallites

Two-photon absorption (TPA) of Tl_1−xIn_1−xSn_xSe₂ (x = 0, 0.1, 0.2, 0.25) was studied at CO₂ laser wavelength 9.4 μm with pulse duration 1 μs. The studies were performed at different temperatures and for the nanocrystallite sizes varying within the 7–200 nm. The nanocrystals were fabricated by mechanical milling with simultaneous acoustical field treatment and porous filter size separation. The studies have shown that the TPA may be enhanced during the decrease of the nanocrystallite sizes below 50–60 nm. There exists also some critical x value at which the TPA value begin substantially to increase. The comparison with other chalcogenide crystals is performed. The studied nanocrystallites are relatively stable to the infrared laser treatment and are not hygroscopic which allow to use them in different IR optoelectronic devices.     

Study of the physical properties of PLD grown cobalt doped nanocrystalline Zn0.9Cd0.1S thin films

We report a systematic study of structural, optical, and magnetic measurements on Zn_0.9Cd_0.1S:yCo films in the concentration range of 0.005 ≤ y ≤ 0.05 M using pulsed laser deposition technique. Structure, composition analysis, and optical measurements revealed that Cobalt is incorporated into the lattice, as Co²⁺ substituting Zn²⁺ ions, forming a solid solution with cubic structure instead of Cobalt precipitates. Low temperature magnetization measurements reveal a paramagnetic behavior. UV–vis measurements showed a red shift with respect to undoped sample in the energy band gap with increasing Cobalt concentration. Photoluminescence measurements shows ~ 300 times increase in intensity by Cobalt doping in Zn_0.9Cd_0.1S matrix.