Continuous Wave Nd-YAG Laser Research Articles

Optimization of Variable Parameters in Diode Pumped SHG Nd-YAG Lasers

Second Harmonic Generation (SHG) produces many parameters which are the consequences of interaction of fundamental incident power  and those created inside the second harmonic cavity, external employing monolithic crystals. In this study, a low power of  continuous wave (CW) Nd-YAG laser with principal output of  and maximum power of  theoretically was used. The crystal is [MgO: LiNbO3] which is lithium niobate, magnesium oxide doped with specific optical properties explained, the parameters in questions are both reflection  and circulating  powers in the second harmonic cavity. Both are functions of fundamental incident power . The results are compared with their experimental correspondents and interpretation for the causes is discussed.

Synthesis, band gap structure and third order non-linear optical properties of zinc tungsten oxide nanocomposite using a single CW laser beam.

In this study, a composite of zinc tungsten oxide nanoparticles (W-ZnO NPs) has been synthesized via mixing Na2WO4 and zinc acetate in water, followed by dropwise addition of NaOH. The synthesized W-ZnO NPs were characterized using measurement methods such as XRD, dynamic light scattering (DLS), Scanning electron microscopy (SEM) and UV-Vis. Also, the results were compared with the pure synthesized ZnO and WO3 NPs. Non-linear optical properties of the synthesized composite were measured using the Z-scan technique with a continuous wave Nd-Yag laser. The negative non-linear absorption coefficient of the components was obtained which indicates that the saturation absorption occurred in this composite. In comparison with pure ZnO NPs, non-linear absorption decreases which can be attributed to the negligible optical response of WO3 structures. Also, the negative value of the close aperture Z-scan curve shows that the thermal lensing effect is the main reason for the third-order non-linear refraction.

Spatial Variation of Thermokinetics and Associated Microstructural Evolution in Laser Surface Engineered IN718: Precursor to Additive Manufacturing

The spatial variation of thermokinetic parameters has a significant influence on solidification and microstructural aspects such as grain orientation, types and dimensions of the microstructural features, and crystallographic defects. In laser-based additive manufacturing, these factors are mainly dependent on the process parameters and have a wide implication on the microstructural aspects and, in turn, on the mechanical properties. In view of this, the current study focuses on the spatial variation on thermokinetic parameters such as cooling rate, thermal gradient (G), and solidification velocity (R) within the melt pool formed during laser processing of IN718. The continuous-wave Nd-YAG laser was employed at a laser fluence of 14.85, 19.10, and $$23.34\text { J/mm}^2$$ with varying power (700, 900, 1100 W) at a constant scanning speed of 100 mm/s. The finite element method-based multiphysics heat transfer model, coupled with the dynamic fluid flow, was developed to predict these parameters. The model was correlated with microstructural aspects such as melt pool dimensions, orientation of columnar grains, and secondary dendritic arm spacing. The cumulative diffusion length of Nb obtained via thermo-diffusion calculation during multiple heating/cooling cycles was enough to dissolve the fine intragranular plate-shaped $$\delta $$ precipitates in the heat-affected zone.The spatial variation of the G/R ratio recognized the transition of columnar to equiaxed solidification grains which was associated with the G/R ratio lower than $$10 \text {K s/mm}^2$$ in the top region ( $$\sim 25 \mu \text {m}$$ ) of the melt pool. In addition, the coupled solid mechanics model predicted the evolution of thermal stresses during solidification of the melt pool under a high thermal gradient, which marked the generation of high dislocation density in the solidified melt pool.

Development of graded composition and microstructure on Inconel 718 by laser surface alloying with Si, Al and ZrB2 for improvement in high temperature oxidation resistance

The present study evaluates the scope of improvement of oxidation resistance of Inconel 718 (IN718) by laser surface alloying (LSA) with Si, Al and ZrB2 using a 0.5 kW continuous wave Nd-YAG laser. The alloyed zone (AZ) is free of macro-defects (porosity, crack, etc.) and contains microstructural and compositional gradation along vertical depth from the top surface until the AZ-substrate interface. Detailed microstructural and phase evolution studies indicate that the AZ consists of multiple intermetallic phases/compounds of Si, Al or Zr with multi-phase eutectic aggregate including Ni-rich matrix phase. The identity, size, morphology and relative amount of these phases vary with LSA parameters and vertical depth within the AZ. Accordingly, the microhardness profile along depth corroborates such graded microstructure and phase aggregate confined to the AZ. Isothermal oxidation studies at 900 °C show significant improvement in oxidation resistance due to LSA in comparison to that of as-received IN718, particularly in case of LSA with Si. Post oxidation studies reveal that the oxide scale consists of adherent oxides like SiO2, Al2O3 or ZrO2, in addition to several intermetallic phases pre-existing in the AZ prior to oxidation. Thus, it follows that the intermetallic phase rich AZ developed by LSA is adherent, defect-free, strong and offers very high resistance to oxidation in IN718 at elevated temperature.

SiC and Al surface cladding of Ti-6Al-4V for improved wear properties – The binary advantage

Ti-6Al-4V enjoys high specific strength, toughness and excellent corrosion resistance, but suffers high friction coefficient, severe adhesive wear and sensitivity to fretting wear. Laser surface cladding is one of the surface modification techniques used for improving on these demerits. Using a 4.4Kw continuous wave Nd-YAG laser processor, the surface cladding of as received Ti-6Al-4V alloy was done with mixtures of SiC and Al powders in different ratios. The SiC powder can serve as reinforcing particles and helps improve surface wear properties in resulting surface metal matrix composite while aluminium improves on the wetting between the metal and the reinforcement SiC phase. The success of this, however, depends on the careful optimisation of the powder ratio, which dictates the resulting phases and microstructural evolutions. Study of the cladding with scanning electron microscope (energy dispersive spectroscopy), optical microscope and x-ray diffraction revealed formation of intermetallic phases such as AlSiTi2, Ti7Al5Si12, TiSi2, AlSi3Ti2, Al6Ti19, Ti2VAl, AlTi3, AlCTi2, Ti3SiC2 and Ti5Si4, which should enhance micro-hardness and tribological properties of the surface relative to the bulk as-received alloy. 90:10 weight percentage ratio of SiC and Al powder mixture gave the best microhardness with a value of 1169.95 Hv, compared to 323.67 Hv of the as-received, and mass loss under abrasive wear tests was only 40% of the as received. The morphology obtained for the abraded surfaces is also indicative of this improvement. In carefully optimised proportions and laser condition, the binary combination of Al and SiC powders suffice for well improved Ti-6Al-4V surface properties.

Application of Continuous Wave ND-YAG Laser for improving Surface Roughness of Cp-Titanium

Application of Continuous Wave ND-YAG Laser for improving Surface Roughness of Cp-Titanium

Third harmonic generation and thermo-physical properties of benzophenone single crystal for photonic applications

A well crystallized Benzophenone single crystal was successfully grown by vertical semi transparent Bridgman technique. The lattice parameters of the grown crystal were established by single crystal x-ray diffraction technique. Fourier transform infrared spectroscopy was performed to determine the functional groups. The UV-NIR analysis revealed that the Benzophenone crystal has high transmittance in the entire visible region and the lower cutoff wavelength has been found to be 381 nm. The optical band gap energy was calculated and it is found to be 3.08 eV. The various linear optical parameters such as, Extinction coefficient (k), Refractive index (n), Reflectance, Complex dielectric constant, Optical susceptibility, Electrical conductivity and Optical polarization of the grown crystal were estimated and its variation with respect to incident photon energy was examined. Furthermore, the third order nonlinear optical properties were investigated by the z-scan technique using continuous wave Nd-YAG laser. The obtained thermophysical properties making use of photoacoustic spectroscopy show the superiority of the crystal over few other standard NLO materials.

Laser surface modification of 316L stainless steel.

Medical grade 316L stainless steel was laser surface melted (LSM) using continuous wave Nd-YAG laser in argon atmosphere at 1 and 5 mm/s. The treated surfaces were characterized using electron backscatter diffraction to study the influence of top surface crystallographic orientation and type of grain boundaries on corrosion resistance, wettability, and biocompatibility. The laser scan velocity was found to have a marginal influence on the surface roughness and the type of grain boundaries. However, the crystal orientation density was found to be relatively high in 1 mm/s samples. The LSM samples showed a higher concentration of {101} and {123} planes parallel to the sample surface as well as a higher fraction of low-angle grain boundaries. The LSM samples were found to exhibit better surface wettability and enhanced the viability and proliferation of human fetal osteoblast cells in vitro when compared to the untreated samples. Further, the corrosion protection efficiency of 316L stainless steel was improved up to 70% by LSM in as-processed condition. The increased concentration of {101} and {123} planes on surfaces of LSM samples increases their surface energy, which is believed to be responsible for the improved in vitro cell proliferation. Further, the increased lattice spacing of these planes and high concentration of low-energy grain boundaries in LSM samples would have contributed to the better in vitro corrosion resistance than untreated 316L stainless steel. Our results indicate that LSM can be a potential treatment option for 316L stainless steel-based biomedical devices to improve biocompatibility and corrosion resistance. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 569-577, 2018.

Treatment of Metastatic Lymph Nodes in the Neck from Papillary Thyroid Carcinoma with Percutaneous Laser Ablation.

To assess the effectiveness of percutaneous laser ablation (PLA) of cervical lymph node metastases from papillary thyroid carcinoma. 24 patients (62.3±13.2year; range 32-80) previously treated with thyroidectomy, neck dissection, and radioiodine ablation underwent ultrasound-guided PLA of 46 (18)FDG-PET/CT-positive metachronous nodal metastases. All patients were at high surgical risk or refused surgery and were unsuitable for additional radioiodine ablation. A 300µm quartz fiber and a continuous-wave Nd-YAG laser operating at 1.064mm were used. Technical success, rate of complications, rate of serological conversion, and local control at follow-up were derived. Fisher's exact test and Mann-Whitney U test were used and Kaplan-Meier curve calculated. Technical success was obtained in all 46 lymph nodes (100%). There were no major complications. Thyroglobulin levels decreased from 8.40±9.25ng/ml before treatment to 2.73±4.0ng/ml after treatment (p=0.011), with serological conversion in 11/24 (45.8%) patients. Overall, local control was obtained in 40/46 (86.9%) lymph nodes over 30±11month follow-up, with no residual disease seen at imaging in 19/24 (79.1%) patients. Local control was achieved in 40/46 (86.9%) lymph nodes at 1year and in all of the 25 nodes (100%) followed for 3years. Estimated mean time to progression was 38.6±2.7m. Ultrasound-guided PLA is a feasible, safe, and effective therapy for the treatment of cervical lymph node metastases from papillary thyroid carcinoma.

Synthesis of poly glycidylmethacrylate grafted azobenzene copolymer: Photosensitivity and nonlinear optical properties

In this work poly glycidylmethacrylate grafted 4-hydroxy-4′-methoxy-azobenzene (Azo-PGMA) was synthesized. For this propose firstly 4-hydroxy-4′-methoxy-azobenzene (AZO) was prepared, then poly glycidylmethacrylate was prepared by free radical polymerization of glycidylmethacrylate in the presence of benzoyl peroxide as initiator under inert atmosphere in dry THF. Finally the homopolymer was functionalized by AZO moieties. The characterization of the synthesized copolymer was carried out by 1H NMR, FT-IR, thermal gravimetric analyze (TGA), differential scanning calorimetry (DSC) and optical polarizing microscope (POM) analysis. The UV–vis studies were carried out on Azo-PGMA copolymer and the results showed that the synthesized Azo-PGMA copolymer has ultra-fast response to UV light and has slow relaxation time. Also the third-order nonlinear optical properties of the Azo-PGMA copolymer and AZO were studied by using Z-scan technique. Nonlinear refraction and absorption coefficients of the above mentioned materials were measured by the closed and open aperture Z-scan method using a continuous wave Nd-YAG laser at 532nm. The positive nonlinear absorption in Azo-PGMA and AZO was investigated at the wavelength of λ=532nm, respectively and the measured values of nonlinear refraction in both of the samples were from the order of 10−8cm2/W.

Tensile behavior of laser treated Fe-Si-B metallic glass

Fe-Si-B metallic glass foils were treated with a linear laser track using a continuous wave Nd-YAG laser and its effect on the overall tensile behavior was investigated. Microstructure and phase evolutions were evaluated using X-ray diffraction, resistivity measurements, and transmission electron microscopy. Crystallization fraction was estimated via the differential scanning calorimetry technique. Metallic glass foils treated with the lower laser fluences (<0.49 J/mm2) experienced structural relaxation, whereas higher laser fluences led to crystallization within the laser treated region. The overall tensile behavior was least impacted by structural relaxation, whereas crystallization severely reduced the ultimate tensile strength of the laser treated metallic glass foils.

Study on Wear and Corrosion Properties of Ti6Al4V Alloy by Laser Gas Nitriding

Titanium alloys have successfully been used as surgical implants. Laser gas nitriding (LGN) is an effective method to improve the wear and corrosion resistance of titanium alloys. A nitride strengthened uniform layer, free of cracks, was obtained on the Ti6Al4V alloy by irradiating with a continuous wave Nd-YAG laser in a N2environment. The microstructure, electrochemical corrosion and tribological behavior of the alloy before and after LGN were studied by SEM, XRD, potentiostat, microhardness tester and tribometer. The results show that the performance and composition of the surface of the Ti6Al4V alloy were significantly improved by LGN, with better corrosion resistance in simulated body fluid and better wear resistance.

Electrochemical Corrosion Behavior of Laser Gas Nitrided Layer on the NiTi Shape Memory Alloy in Hank’s Solution

A nitrided layer was formed on the NiTi shape memory alloy (SMA) after being irradiated by a continuous wave Nd-YAG laser in a N2 environment. With optimum process parameters, a compact laser modified gradient layer reinforced with fine TiN particles was achieved. Electrochemical measurements of the laser gas nitrided layer on the NiTi SMA showed that the corrosion potential and the breakdown potential were increased while the corrosion current was decreased as compared with the untreated the NiTi SMA. The polarization resistance of the laser gas nitrided layer on the NiTi SMA was increased significantly while the capacitance was decreased. Based on the EIS spectra, a simple model and an equivalent circuit were proposed to describe the electrode-electrolyte interfaces.

A facile route to produce Fe–Al intermetallic coatings by laser surface alloying

This work studies the feasibility of obtaining iron aluminide coatings on pure iron substrate by means of laser surface alloying (LSA). Pure Al was plasma spray coated on pure Fe substrate and subsequently laser alloyed by using multi mode continuous wave Nd-YAG laser at different output power and scanning rates. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. Detailed optical, SEM–EDX and XRD investigations were performed to characterize the phases formed during laser alloying. At 300 W laser output power, Al rich intermetallic phases mainly FeAl3, Fe2Al5 had formed with scanning rate in the range of 100–400 mm/min. However, at high power outputs (500 W) Fe–Al intermetallic phase had formed, which was found to have sound and crack free interface with the substrate.

Characterization of the laser gas nitrided surface of NiTi shape memory alloy

Owing to its unique properties such as shape memory effects, superelasticity and radiopacity, NiTi alloy is a valuable biomaterial for fabricating implants. The major concern of this alloy for biological applications is the high atomic percentage of nickel in the alloy and the deleterious effects to the body by the corrosion and/or wears products. In this study, a continuous wave Nd-YAG laser was used to conduct laser gas nitriding on the substrate of NiTi alloy. The results show that a continuous and crack-free thin TiN layer was produced in situ on the NiTi substrate. The characteristics of the nitrided surface layer were investigated using SEM, XRD, XPS and AAS. No nickel signal was detected on the top surface of the laser gas nitrided layer. As compared with the mechanical polished NiTi alloy, the nickel ion release rate out of the nitrided NiTi alloy decreased significantly in Hanks’ solution at 37 °C, especially the initial release rate.

Analysis of laser gas nitrided titanium by X-ray photoelectron spectroscopy

Nitriding is an effective method to improve the surface properties of titanium for many demanding applications such as surgical implants. In this study, a continuous wave Nd-YAG laser was used to conduct laser gas nitriding (LGN) on the substrate of commercial pure titanium. The surface characteristics of the titanium before and after the LGN process were analyzed by X-ray photoelectron spectroscopy. The results showed that most contamination signals were eliminated by sputtering the tested sample for 1 min. The nitrided surface layer created by LGN on titanium was found to be comprised of TiN, TiN x O y , TiO 2, and TiC. TiO 2 was found only existed at the outmost surface layer and the TiN concentration in the nitrided layer increased with increasing depth. Titanium carbide was not detected on the surface of the mechanical polished Ti, but on the laser gas nitrided sample.

Enhancement of cavitation erosion and corrosion resistance of brass by laser surface alloying with Ni–Cr–Si–B

Brass (Cu–38% Zn–1.5% Pb) was surface-alloyed with a hardfacing Ni–Cr–Si–B powder (Ni–16.5% Cr–3.5% Si–3.8% B–15.5% Fe–<1% C) using a high-power continuous-wave Nd-YAG laser with different processing parameters for improving the cavitation erosion and corrosion resistance in 3.5 wt.% NaCl solution. The cavitation erosion resistance R e (defined as the reciprocal of the mean erosion rate) of the alloyed layer ranged from 6.10- to 9.06-fold that of the brass substrate, and was found to be closely related to the hardness of the alloyed layer. The corrosion resistance was also improved, as indicated by a noble shift in the pitting potential and a reduction in the corrosion current density. The difference in the cavitation erosion and corrosion behavior of various specimens is discussed in relation to their microstructures and structures via studies using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The present study also indicated that it is difficult to achieve maximum improvement in cavitation erosion and corrosion resistance simultaneously.

Improvement Of Cavitation Erosion Resistance and Corrosion Resistance Of Brass by Laser Surface Modification

AbstractLaser surface modification of brass (Cu-38Zn-1.5Pb) using AISiFe and NiCrSiB alloy was achieved by using a 2kW continuous wave Nd-YAG laser with the aim of improving the cavitation erosion resistance and corrosion resistance. The alloying powder was preplaced on the brass substrate by thermal spraying to a thickness of 350µm, followed by laser beam scanning to effect melting, mixing and alloying. A modified surface was achieved by overlapping of adjacent tracks. The cavitation erosion resistance and the anodic polarization characteristics of the laser surface modified specimens in 3.5% NaCI solution at 23°C were studied by means of a 20kHz ultrasonic vibrator at a peak to peak amplitude of 60µm and a potentiostat respectively. The cavitation erosion resistance of the specimens modified with AlSiFe and NiCrSiB was improved by a factor of 3 and 7 respectively, compared with that of the brass substrate. Potentiodynamic test, however, indicated that the corrosion resistance of specimens modified with AlSiFe deteriorated, as reflected by a shift of the polarization curve towards higher current densities. On the other hand, the corrosion resistance of specimens modified with NiCrSiB was significantly improved, as evidenced by the presence of a passive region (from −175 mV to −112 mV) and a reduction in the anodic current density by at least an order of magnitude compared with the substrate at the same anodic potential. The hardness profile and the compositional profile were measured using a Vickers hardness tester and EDX respectively. The microstructure and the surface morphology of the specimens were investigated with the aid of SEM and optical microscopy.

1.53 μm photoluminescence of Er 3+ in perovskite manganite thin films

Highly oriented perovskite manganite (La 0.55Er 0.05Ca 0.4MnO 3) thin films were deposited on silicon (1 0 0) substrates by magnetron sputtering. Photoluminescence of Er 3+ at around λ=1.53 μm has been detected at room temperature when excited by a continuous wave Nd-YAG laser at 1.064 μm. The photoluminescence intensity is proportional to the excitation laser intensity. Based on optical absorption measurements, the energy transfer from the manganese ion to the erbium ion is proposed as the likely mechanism contributing to the observed photoluminescence of Er 3+.

Laser surface modification of UNS S31603 stainless steel using NiCrSiB alloy for enhancing cavitation erosion resistance

Laser surface modification using NiCrSiB alloy (Ni −16.5Cr −15.5Fe −3.5Si −3.8B −0.1C) on austenitic stainless steel UNS S31603 (Fe −17.6Cr −11.2Ni −2.5Mo −1.4Mn −1.4Cu −0.4Si −0.03C) was achieved by using a 2 kW continuous wave Nd-YAG laser. The cavitation erosion and pitting corrosion characteristics of the laser surface modified UNS S31603 in 3.5% NaCl solution at 23 °C were studied by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 μm and a potentiostat, respectively. The NiCrSiB alloy layer was flame sprayed on the surface of UNS S31603 stainless steel. The surface was then scanned with the laser beam. The melt depth and dilution of the sprayed layer with the substrate material increased with the decrease of scanning speed. At low dilution ratio of sprayed layer thickness to melt depth, less secondary phases such as CrB, CrB 2, Fe 2B and M 7(CB) 3 and low hardness were observed in the laser-modified layer. The cavitation erosion resistance R e (reciprocal of the mean depth of penetration) of the laser-modified specimen with a dilution ratio of 0.65 was improved by 2.7 times as compared with that of the as-received UNS S31603 specimen. In addition, the pitting potential was close to that of the as-received UNS S31603 and the protection potential shifted in the noble direction by a substantial amount (from −3 to 121 mV). The R e of the laser surface modified specimen with dilution ratio of 0.88 was improved by four times as compared with that of the as-received UNS S31603 and very close to that of super duplex stainless steel UNS S32760 (Fe −25.6Cr −7.2Ni −4Mo −0.6Mn −0.7Cu −0.8W −0.3Si −0.2N −0.03C). However, its pitting potential was lowered from 359 to 50 mV and its protection potential shifted in the active direction from −3 to −238 mV. On the other hand, the degree of pitting damage as judged from the pitting morphology was less severe in the laser surface modified specimens. The R e of laser surface modified UNS S31603 was found to be linearly related to hardness. The deformation mechanism by cavitation erosion of the laser-modified specimens was also investigated.