Laser Irradiation Process Research Articles

Theoretical and experimental research on laser-induced damage of cylindrical subwavelength grating.

We designed and fabricated two-dimensional cylindrical subwavelength gratings (SWGs) on fused silica for use in 1064 nm laser system. The transmittance and laser-induced damage threshold (LIDT) under the irradiation of 1064 nm pulses were performed, and a lower LIDT compared to blank fused silica was obtained. To understand damage mechanism quantitatively, macro-temperature on the SWGs integrated fused silica and micro-Electric field, micro-thermal-stress distribution on SWGs during the laser irradiation process were investigated by Finite Element Analysis, and the comparison between theoretical and experimental research indicated the presence of absorption centers and the non-uniform thermal mechanical distribution of SWGs contributed to the LIDT reduction on SWGs integrated fused silica.

Superhydrophobic laser-ablated stainless steel substrates exhibiting Cassie–Baxter stable state

In order to produce long-lasting, non-wettable surfaces, femtosecond laser ablation process was used to produce micro/nano structures on metallic surfaces. The effects of femtosecond laser irradiation process parameters (fluence, scanning speed and laser beam overlap) on the hydrophobicity of the resulting micro/nano-patterned morphologies on stainless steel were studied in detail. Seven distinctly different micro/nano patterns, namely nano-rippled, paraboloidal, sinusoidal, triple roughness, cauliflowered, tulip and scaly patterns, were fabricated. The latter pattern (scaly) was found to be identical to that of the butterfly wing structure. All patterns were classified according to laser intensity and scanning speed. Consequently, the fabricated substrates were chemically treated by silanization (Young contact angle (CA) of about 105°) in order to examine the additional effects of nanopatterning on wettability. The analysis of wettability revealed enhanced superhydrophobicity for most of these structures, particularly for the cauliflowered and scaly patterns with CAs in excess of 160° and contact angle hysteresis of less than 10°. Finally, the cauliflowered pattern was found to possess a stable composite state, which is important for certain applications such as friction (Cassie–Baxter).

Electronic Reconstruction of α-Ag2WO4 Nanorods for Visible-Light Photocatalysis

α-Ag2WO4 (AWO) has been studied extensively due to its H2 evolution and organic pollution degradation ability under the irradiation of UV light. However, the band gap of AWO is theoretically calculated to be 3.55 eV, resulting in its sluggish reaction to visible light. Herein, we demonstrated that, by using the electronic reconstruction of AWO nanorods upon a unique process of laser irradiation in liquid, these nanorods performed good visible-light photocatalytic organics degradation and H2 evolution. Using commercial AWO powders as the starting materials, we achieved the electronic reconstruction of AWO by a recrystallization of the starting powders upon laser irradiation in liquid and synthesized AWO nanorods. Due to the weak bond energy of AWO and the far from thermodynamic equilibrium process created by laser irradiation in liquid, abundant cluster distortions, especially [WO6] cluster distortions, are introduced into the crystal lattice, the defect density increases by a factor of 2.75, and uneven intermediate energy levels are inset into the band gap, resulting in a 0.44 eV decrease of the band gap, which modified the AWO itself by electronic reconstruction to be sensitive to visible light without the addition of others. Further, the first-principles calculation was carried out to clarify the electronic reconstruction of AWO, and the theoretical results confirmed the deduction based on the experimental measurements.

Laser-induced chemical transformation of graphene oxide–iron oxide nanoparticles composites deposited on polymer substrates

Ultraviolet laser irradiation of films composed of graphene oxide (GO) and GO–magnetite (Fe3O4) nanoparticles deposited on polydimethylsiloxane substrates is carried out. The irradiations are performed in vacuum and ammonia-rich gas environments. Electron and scanning probe microscopies reveal a rippling process in GO sheets as the accumulation of laser pulses proceeds, being the effect more pronounced with the increase of laser fluence. X-ray photoelectron spectroscopy analyses point to laser-induced chemical reaction pathways in GO completely different depending on the environment and the presence or absence of Fe3O4 nanoparticles. It is demonstrated that GO-based films with diverse type of oxygen- and nitrogen-containing chemical groups can be obtained by means of laser irradiation processes. The sheet resistance of these materials is also correlated to their structure and composition.

Superhydrophobic laser ablated PTFE substrates

The effect of femtosecond laser irradiation process parameters (fluence, scanning speed and beam overlap) on the wettability of the resulted micro/nano-patterned morphologies on polytetrafluoroethylene is studied in detail. Several distinctly different micro/nano-patterns were fabricated including uniaxial and biaxial patterns. In particular, using biaxial scanning well defined pillared morphology was fabricated. The wettability analysis of the biaxially scanned samples revealed enhanced superhydrophobicity exhibiting high contact angles and low contact angle hysteresis.

Ultrafast Graphene Growth on Insulators via Metal-Catalyzed Crystallization by a Laser Irradiation Process: From Laser Selection, Thickness Control to Direct Patterned Graphene Utilizing Controlled Layer Segregation Process.

Despite the vast progress in chemical vapor deposition (CVD) graphene grown on metals, the transfer process is still a major bottleneck, being not devoid of wrinkles and polymer residues. In this paper, a structure is introduced to directly synthesize few layer graphene on insulating substrates by a laser irradiation heating process. The segregation of graphene layers can be manipulated by tuning the metal layer thickness and laser power at different scanning rates. Graphene deposition and submicrometer patterning resolution can be achieved by patterning the intermediate metal layer using standard lithography methods in order to overcome the scalability issue regardless the resolution of the laser beam. The systematic analysis of the process based on the formation of carbon microchannels by the laser irradiation process can be extended to several materials, thicknesses, and methods. Furthermore, hole and electron mobilities of 500 and 950 cm(2) V(-1) s(-1) are measured. The laser-synthesized graphene is a step forward along the direct synthesis route for graphene on insulators that meets the criteria for photonics and electronics.

Fabrication of polymer microcomponents using CO2 laser melting technique

A new method of laser melting molding to produce high-efficiency and high-quality polymer microcomponents was proposed. Numerical simulation was used to analyze the temperature changes of polymer melt during the laser irradiation process. An orthogonal experiment was also employed to investigate the factors influencing molding accuracy. The molding experiments were conducted on molds with various degrees of roughness, and the surface quality of the molded pieces was tested. The simulation analysis and experimental results showed that the laser power plays a critical role in improving the repetition accuracy. The next factors are irradiation time and mold temperature, followed by molding force. Optimized technological parameters (1.2 W of laser power, 6 mm of laser beam width, 6 s irradiation time, 150 N molding force, and 80 °C mold temperature) were applied to obtain a molded pieces with high repetition accuracy and a microstructure dimensional deviation of less than 1 µm. Using a mold with lower surface roughness provides that we can obtain a molded piece with lower roughness, the roughness difference between the mold and the molded piece was less than 0.012 µm.

Laser irradiated bending characteristics of the ultra-high strength steel sheets

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. This is a new manufacturing technique that forms the metal sheet only by thermal stress. Analyzing the effect of process parameters on the deformation behavior is very important for the application of laser forming process to the real product. In this paper, deformation mechanism and bending behaviors of the ultra-high strength steel sheet SPFC1180Y were investigated numerically and experimentally. Coupled thermo-mechanical FE simulations were firstly conducted to analyze the response related to the bending angle of a square sheet part. The thermo-mechanical behaviors during the straight-line laser irradiated process were presented in terms of temperature, stress and strain. Experiments were then carried out to identify the deformation behaviors with various process parameters such as laser powers, scanning speeds, number of laser irradiations and beam diameters. Results indicate that the bending angle increases with the increase of the laser powers and the absorptivity related to the scanning speeds and number of irradiations. The results also provide a relationship between the bending angle and the line energy imposed on the specimen. The relationship obtained from the paper can be used as a process guide-lines in the laser irradiated bending of SPFC1180Y steel sheets.

Distinct photoresponse in graphene induced by laser irradiation

The graphene-based photodetector with tunable p-p+-p junctions was fabricated through a simple laser irradiation process. Distinct photoresponse was observed at the graphene (G)-laser irradiated graphene (LIG) junction by scanning photocurrent measurements, and its magnitude can be modulated as a result of a positive correlation between the photocurrent and doping concentration in LIG region. Detailed investigation suggests that the photo-thermoelectric effect, instead of the photovoltaic effect, dominates the photocurrent generation at the G-LIG junctions. Such a simple and low-cost technique offers an alternative way for the fabrication of graphene-based optoelectronic devices.

Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film

A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.

Reversible nanodiamond-carbon onion phase transformations.

Because of their considerable science and technical interest, nanodiamonds (3-5 nm) are often used as a model to study the phase transformation between graphite and diamond. Here we demonstrated that a reversible nanodiamond-carbon onion phase transformation can become true when laser irradiates colloidal suspensions of nanodiamonds at the ambient temperature and pressure. Nanodiamonds are first transformed to carbon onions driven by the laser-induced high temperature in which an intermediary bucky diamond phase is observed. Sequentially, carbon onions are transformed back to nanodiamonds driven by the laser-induced high temperature and high pressure from carbon onions as nanoscaled temperature and pressure cell upon the laser irradiation process in liquid. Similarly, the same bucky diamond phase serving as an intermediate phase is found during the carbon onion-to-nanodiamond transition. To have a clear insight into the unique phase transformation the thermodynamic approaches on the nanoscale were proposed to elucidate the reversible phase transformation of nanodiamond-to-carbon onion-to-nanodiamond via an intermediary bucky diamond phase upon the laser irradiation in liquid. This reversible transition reveals a series of phase transformations between diamond and carbon allotropes, such as carbon onion and bucky diamond, having a general insight into the basic physics involved in these phase transformations. These results give a clue to the root of meteoritic nanodiamonds that are commonly found in primitive meteorites but their origin is puzzling and offers one suitable approach for breaking controllable pathways between diamond and carbon allotropes.

A non-destructive surface burn detection method for ferrous metals based on acoustic emission and ensemble empirical mode decomposition: from laser simulation to grinding process

Grinding is usually done in the final finishing of a component. As a result, the surface quality of finished products, e.g., surface roughness, hardness and residual stress, are affected by the grinding procedure. However, the lack of methods for monitoring of grinding makes it difficult to control the quality of the process. This paper focuses on the monitoring approaches for the surface burn phenomenon in grinding. A non-destructive burn detection method based on acoustic emission (AE) and ensemble empirical mode decomposition (EEMD) was proposed for this purpose. To precisely extract the AE features caused by phase transformation during burn formation, artificial burn was produced to mimic grinding burn by means of laser irradiation, since laser-induced burn involves less mechanical and electrical noise. The burn formation process was monitored by an AE sensor. The frequency band ranging from 150 to 400 kHz was believed to be related to surface burn formation in the laser irradiation process. The burn-sensitive frequency band was further used to instruct feature extraction during the grinding process based on EEMD. Linear classification results evidenced a distinct margin between samples with and without surface burn. This work provides a practical means for grinding burn detection.

Fabrication of Freestanding Graphene Nanoribbon Network by Utilizing Laser Technology

ABSTRACTLaser is used to produce graphene nanoribbons (GNRs) by unzipping carbon nanotubes (CNTs). It is found that laser can not only unzip CNTs, but also join GNRs through covalent reconnections. Because the CNTs are aligned in a freestanding CNT sheet, the laser irradiation process results in a freestanding GNR network. Experimental results show that the expected results can be achieved by controlling the delivery of laser beam energy to the sheet. Moreover, this process is a solid-state process and a scalable manufacturing process.

In situ monitoring of excimer laser annealing of tin-doped indium oxide films for the development of a low-temperature fabrication process

In this paper, in situ monitoring of excimer laser irradiation processing is examined for application to the production of thin films of transparent conductive oxides (TCOs) such as tin-doped indium oxide (ITO). Numerical simulations reveal that differences in the thin film state, for example, in the dopant levels, could greatly affect the proper laser fluence, suggesting the importance of in situ monitoring of the excimer laser processing. The thermal emission signals of ITO thin films under irradiation by a pulsed ultraviolet laser were successfully detected in situ with a near-infrared sensor on a nanosecond timescale. Non-monotonic decay of the thermal radiation from the ITO thin films was observed under XeCl laser irradiation above a certain fluence. At this fluence, the surface morphology of the ITO thin films observed by atomic force microscopy changed to a microstructure reflecting melting and solidification. This correspondence between the thermal radiation and morphology suggests that the observed non-monotonic decay was caused by recalescence upon solidification and that the in situ monitoring technique can be used to detect such phase changes.

Numerical and experimental investigation on laser irradiated bending process of advanced high strength steel

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. This is a new manufacturing technique that forms the metal sheet only by thermal stress. Analysing temperature and stress fields are very important to identify the deformation mechanism in laser forming. In this paper, temperature distributions and deformation behaviours of DP980 steel sheets are investigated numerically and experimentally. Coupled thermomechanical finite element simulations are firstly conducted to evaluate the response related to the bending angle of a square sheet part. The effects of process parameters such as laser power and scanning speed are analysed numerically. The thermomechanical behaviours during the straight line heating process are presented in terms of temperature, stress and strain. Experiments are then carried out to validate the simulation results. It is observed that the numerical results are in good agreement with the experimental results. Results also represent the relationship between line energy and bending angles for laser bending of DP980 steel sheets.

Local Modification of Speed of Sound in Lithium Alumino-Silicate Glass/Ceramic Material by Pulsed Laser Irradiation and Thermal Processing

Glass and glass/ceramics are now used in modern devices with increasing frequency. A list of the notable material properties commonly will not include a capability to guide ultrasonic waves. The photosensitive glass ceramics (PSGCs), an old invention with recent technological rebirth, may enable this capability. The speed of sound (SoS) has been measured at an ultrasonic frequency (75 MHz) in a commercially available PSGC material. The measurements are made using a pulse echo time-of-flight (TOF) technique as a function of UV laser exposure and thermal processing. The measured increase in the SoS correlates with the density of crystalline matter present, which can be metered by controlling the exposure dose. For the Li2SiO3 crystalline phase, the results show the shear (transverse) wave mode velocity can be increased by 4.8% relative to an unexposed area where no crystalline matter exists. The maximum change in velocity for the longitudinal (compressional) wave mode is only 2%. However, by altering the thermal processing protocols to grow the high temperature Li2Si2O5 crystalline phase, the measured change in the SoS increases to 11% and 9%, respectively. These results permit the volumetric patterning of delay lines by laser direct write techniques for generating complex profile ultrasonic wave patterns. Moreover, by patterned 3D shaping (i.e., photostructuring), ultrasound energy can be harnessed and utilized to advantage.

Femtosecond laser irradiation of metallic surfaces: effects of laser parameters on superhydrophobicity

This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence and scanning speed) on the hydrophobicity of the resulting micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nano-structures. All of the produced structures were classified according to a newly defined parameter, the laser intensity factor (LIF); by increasing the LIF, the ablation rate and periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluoroalkylsilane agent. Analysis of the wettability revealed enhanced superhydrophobicity for most of these structures, particularly those possessing the triple roughness pattern that also exhibited low contact angle hysteresis. The high permanent superhydrophobicity of this pattern is due to the special micro/nano-structure of the surface that facilitates the Cassie–Baxter state.

Effect of Temperature Induced by Laser Irradiation Processing on Fatigue Damage Repairing for Copper Thin Film

Based on laser irradiation processing experiment for repairing damaged copper thin film specimens, the effect of temperature field induced by pulsed laser surface irradiation on fatigue damage repairing of copper thin film was studied by numerical simulation method. First the temperature field of copper thin film after laser irradiation was analyzed by ANSYS under different pulse energies and pulse numbers. Then the surface morphologies of copper thin film specimens were observed by optical microscope before and after laser surface irradiation. The results showed that laser irradiation processing has a better effect on fatigue damage repairing when the temperature induced by laser surface irradiation reaches about 1200 °C. A slightly melted morphology on the surface of copper thin film was observed in this case. In addition, except for the full healing of fatigue damage, the total fatigue life was increased about 2 times at the nominal stress level of 120MPa.

Approach to recovery of fatigue damage for copper film by pulsed laser irradiation

Based on pulsed laser irradiation processing, an approach to the recovery of fatigue damage was investigated by an excimer laser for copper film with thickness of 25 μm. First, optimal parameters of laser irradiation were identified by the obtained fatigue life results under different laser treatment conditions. Then, the specimens with different amounts of fatigue damage were treated by the obtained optimal laser parameters. The results showed that the copper film can show a good degree of hardening and a smooth surface feature after the specimen surface was slightly melted by the laser irradiation, which makes the residual fatigue life be extended. When fatigue damage is less than 70%, the damage can be recovered by pulsed laser irradiation treatment. The obtained residual fatigue life of specimens is about 6 times that of no laser treatment.

Physical characteristics of localized surface plasmons resulting from nano-scale structured multi-layer thin films deposited on D-shaped optical fiber

Novel surface plasmonic optical fiber sensors have been fabricated using multiple coatings deposited on a lapped section of a single mode fiber. UV laser irradiation processing with a phase mask produces a nano-scaled surface relief grating structure resembling nano-wires. The resulting individual corrugations produced by material compaction are approximately 20 μm long with an average width at half maximum of 100 nm and generate localized surface plasmons. Experimental data are presented that show changes in the spectral characteristics after UV processing, coupled with an overall increase in the sensitivity of the devices to surrounding refractive index. Evidence is presented that there is an optimum UV dosage (48 joules) over which no significant additional optical change is observed. The devices are characterized with regards to change in refractive index, where significantly high spectral sensitivities in the aqueous index regime are found, ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity.