Enhancement Of Laser Power Research Articles

Optimization of processing parameters for LPBF-manufactured CoCr alloys based on laser volume energy density

In this paper, the finite element method (FEM) and experiments were adopted to optimize the processing parameters of laser powder bed fusion-manufactured cobalt-chromium (CoCr) alloys on the basis of laser volume energy density. According to simulation results, both the maximum temperature, heat-affected zone and cooling rate of molten pool increased with the enhancement of laser power and scanning speed even under the same laser volume energy density. By conducting relevant experiments, it is found that the phase transformation, microstructure and mechanical properties were also influenced by the variation of laser power and scanning speed, and the LPBF-processed CoCr alloys with excellent forming quality could be acquired when the laser power was 160 W, and the scanning speed was 750 mm/s. Therefore, it is impracticable to optimize the processing parameters only on the basis of laser volume energy density, various methods should be employed to complete the whole optimization procedure.

Phase transition and formation of inorganic fullerene type nanostructure in WS2 nanosheet system under laser excitation

Here in, laser power and energy dependant chemical and structural changes in WS2 nanosheets have been reported. The nanosheets were obtained through liquid phase exfoliation in N-methyl pyrrolidone (NMP). Simultaneous laser irradiation and Raman spectral analysis were performed on the nanosheets. It was observed that laser power enhancement leads to further exfoliation and red shift of prominent phonon modes E12g and A1g in the nanosheets. Oxidation of the nanosheets was also witnessed with a minimum 50 mJ of laser irradiation. Raman spectral analysis also reveals the transition of WS2 from 2H (hexagonal symmetry, one layer per repeat, trigonal prismatic coordination to 1T (tetragonal symmetry, one layer per repeat, octahedral coordination) crystallographic arrangements with a minimum 50 mJ of laser energy. Formation of incipient inorganic fullerene type nanostructures was also confirmed in the laser irradiated WS2 nanosheets. It is anticipated that such experimental findings will boost further laser induced treatment of transition metal dichalcogenides for novel applications.

Influence of laser welding power on steel/CFRP lap joint fracture behaviors

Dual-phase steel DP590 and carbon fibre reinforced polymer (CFRP) were successfully joined by laser welding. Experiments and numerical simulations were performed to clarify the influence of laser power on the joint characteristic, bonding mechanism and fracture behavior. The results indicate that the melting width and depth of CFRP increased with the enhancement of laser power. With relatively low laser power, un-bonded steel/CFRP interface was formed due to the insufficient melting of resin matrix and interfacial residual stress resulted from thermal expansion mismatch between steel and CFRP. Compact-bonding was produced with the laser power range of 400–700 W. Decomposition of CFRP at the interface occurred with the further increase of laser power to 800 W due to excessively high peak temperature. The highest tensile-shear peak load of 3855 N was produced at 700 W laser power. Three different fracture modes were found in the joints with different laser powers, i.e., interfacial fracture (IF) at 300 W and 400 W, cohesion fracture (CF) in CFRP at 500 W and 600 W, and interface fracture at inner region together with cohesion fracture at outer region of the bonding interface (IF + CF) at 700 W and 800 W. X-ray photoelectron spectroscopy results showed that C-M and O-M chemical bonds were formed at the interface due to the reaction between resin matrix and DP590. Stronger O-M and C-M chemical bonds produced at higher laser power were beneficial for the improvement of fracture load.

Dynamics of femtosecond synthesized coronary profile laser beam filamentation in air

Multiple filamentation in air of high-power ultrashort laser radiation with a transverse intensity profile resembling a corona composed of several annularly distributed independent top-hat sub-beams is theoretically studied. Through the numerical solution of the time-averaged nonlinear Schrödinger equation, we study the spatio-angular dynamics of a near-infrared annular combined beam (CB) along the optical path by varying the number and power of the beamlets (corona-spikes). The evident advances in the use of CB in the multiple-filamentation region manipulation and for achieving long-range filamentation are theoretically revealed. In particular, by adjusting the number and aperture of the constituting sub-beams, it makes it possible to significantly delay the CB filamentation onset distance and increase the filamentation length in air. In addition, at the post-filamentation stage of femtosecond pulse propagation under certain conditions, the CBs exhibit significantly lower angular divergence of their most intense part (post-filamentation light channel) compared to the beams with regular unimodal intensity profiles (Gaussian or plateau-like) that provide enhancement of laser power delivered to the receiver over the atmospheric links.

Thermo-optical properties of EuF2-based crystals

High-power solid state lasers of the mid-IR spectral range are extremely interesting for both basic research and technological applications and they are actively developing at present. However, the implementation of projects with the use of such lasers is hampered by the absence of Faraday isolators (FIs) for the radiation with the corresponding characteristics. The need for such devices is growing with laser power enhancement. They reduce the risk of self-excitation of the damage of amplifiers and optical elements and are a handy tool for organizing multipass schemes. Magneto-active crystals based on Eu2+ ions are promising media for the development of FIs for high-power lasers of the mid-IR spectral range because of the unique combination of their spectral and magneto-optical properties. Thermo-optical characteristics are also of principal importance when operating with high-power laser radiation. This letter presents the results of investigation of thermo-optical constants Q and P of the EuF2.11 solid solution crystal which determines the values of polarization and phase distortions of passing laser radiation. The measured values can be considered as the corresponding values for the EuF2 crystal, which is of greatest interest for the development of FIs for high-power mid-IR lasers. The obtained results can be used to determine the characteristics of FIs based on EuF2 crystals in various implementations of their optical schemes for various parameters of laser radiation. According to the estimates, for the radiation wavelength of 2 μm, the maximum permissible laser power of the Faraday isolator based on one magneto-optical element with [001] orientation will be more than 200 W.

Control of wall thickness and surface morphology of tungsten thin wall parts by adjusting selective laser melting parameters

The tungsten thin wall parts which were used as high-performance collimator devices were fabricated by optimizing selective laser melting laser parameters. The effect of laser power and scan rate on wall thickness and surface morphology of tungsten thin wall parts was investigated, respectively. The results indicated that the wall thickness increased with the enhancement in laser power as a linear relationship. On the contrary, the wall thickness decayed exponentially with the acceleration in laser scan rate. Meanwhile, the wall thickness of the parts fabricated by laser double-pass melting was thinner than that fabricated by laser single-pass melting. In addition, mathematic models for selecting suitable laser power and laser scan rate to fabricate specified tungsten thin wall parts were proposed. Furthermore, the effects of laser parameters on the top surface roughness, adhesive parts and hot cracks were also discussed.

Semiconductor Laser Power Enhancement by Control of Gain and Power Profiles

We present theoretical calculations investigating the output power limitations of GaAs-based semiconductor lasers and the experimental results showing significant improvement of output power. To understand the influence of power limitation mechanisms, semiconductor laser with standard and unfolded cavity designs is studied. Our analysis reveals that an unfolded cavity laser enables more homogeneous longitudinal gain and intracavity optical intensity with reduced levels as compared with the standard cavity. Hence, an unfolded laser has theoretically lower power penalties induced by linear and nonlinear effects. For a 5.7-mm long laser cavity with 100- $\mu \text{m}$ wide aperture, the experimental results demonstrate 21-W output from standard cavity whereas the unfolded cavity design achieves 33-W at 920 nm, which is >55% enhancement of the output, confirming the prediction of the theoretical calculations. The method represents a major step toward understanding semiconductor laser power limitations and realizing higher power output by control of longitudinal gain and power profiles.

Thermo-Optical and Magneto-Optical Characteristics of Terbium Scandium Aluminum Garnet Crystals

Magnetoactive materials are of considerable current interest, primarily for applications in nonreciprocal Faraday devices used for polarization control, optical isolation, optical switching, and modulation. The need for such devices is growing with laser power enhancement. They reduce risk of self-excitation of the amplifiers and optical elements damage and are a handy tool for organizing multipass schemes. However, at high average power of radiation these devices are subject to thermally induced effects that impair their operability and lead to increased losses and to the formation of phase distortions in the transmitted radiation. One of the methods to reduce thermally induced effects is to use in Faraday devices new magnetoactive materials with better thermo-optical properties. This paper is devoted to the study of thermo-optical and magneto-optical characteristics of a unique magnetoactive material-a terbium scandium aluminum garnet (TSAG) crystal. The TSAG has an extraordinary value of optical anisotropy parameter ξ, a Verdet constant 25% higher than the traditionally used terbium gallium garnet crystal and the highest magneto-optical figure-of-merit known in magnetoactive materials at the moment.

Low threshold fiber taper coupled rare earth ion-doped chalcogenide microsphere laser**Project supported by the National Natural Science Foundation of China (Grant Nos. 61177087 and 61435009), the National Key Basic Research Program of China (Grant No. 2012CB722703), the Program for Innovative Research Team of Ningbo City, China (Grant No. 2009B21007) , the K. C. Wong Magna Fund in Ningbo University, the

We report the applications of a low-cost and environmentally friendly chalcogenide glass, 75GeS2-15Ga2S3-10CsI, in building active microsphere laser oscillators. A silica fiber taper is used as the coupling mechanism. With an 808-nm laser diode as a pump source, we show that a high-Q (∼ 6×104) laser mode could be obtained from a 75-μm diameter microsphere that is coupled with a 1.77-μm waist-diameter fiber taper. The threshold of the incident pump power is 1.39 mW, which is considerably lower than those of previously reported free-space coupled chalcogenide microsphere lasers. We also note an apparent enhancement in laser power generated from this chalcogenide microsphere laser.

High finesse optical cavity coupled with a quartz-enhanced photoacoustic spectroscopic sensor.

An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) combined with a high-finesse cavity sensor platform is proposed as a novel method for trace gas sensing. We call this technique Intra-cavity QEPAS (I-QEPAS). In the proposed scheme, a single-mode continuous wave quantum cascade laser (QCL) is coupled into a bow-tie optical cavity. The cavity is locked to the QCL emission frequency by means of a feedback-locking loop that acts directly on a piezoelectric actuator mounted behind one of the cavity mirrors. A power enhancement factor of ∼240 was achieved, corresponding to an intracavity power of ∼0.72 W. CO2 was selected as the target gas to validate our sensor. For the P(42) CO2 absorption line, located at 2311.105 cm(-1), a minimum detection limit of 300 parts per trillion by volume at a total gas pressure of 50 mbar was achieved with a 20 s integration time. This corresponds to a normalized noise equivalent absorption of 3.2 × 10(-10) W cm(-1) Hz(-1/2), comparable with the best results reported for the QEPAS technique on much faster relaxing gases. A comparison with standard QEPAS performed under the same experimental conditions confirms that the I-QEPAS sensitivity scales with the intracavity laser power enhancement factor.

Gain and continuous-wave laser power enhancement with a multiple discharge electric oxygen-iodine laser

Herein the authors report on the demonstration of a 70% enhancement in gain and 98% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine via an increase in flow rates and pressure using multiple discharges in an electric oxygen-iodine laser. O2(aΔ1) is produced by two parallel radio-frequency-excited electric discharges sustained in an O2–He–NO gas mixture, a secondary discharge predissociated the molecular iodine, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.17%cm−1 was obtained and the total laser output power was 12.3W.

Gain and continuous-wave laser power enhancement with a secondary discharge to predissociate molecular iodine in an electric oxygen-iodine laser

Herein the authors report on the demonstration of a 50% enhancement in gain and 38% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine through the addition of a secondary discharge to predissociate the molecular iodine in an electric oxygen-iodine laser. In the primary discharge the O2(aΔ1) is produced by a radio-frequency-excited electric discharge sustained in an O2–He–NO gas mixture, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.10%cm−1 was obtained and the total laser output power was 6.2W.

Nd:YAG Laser Power Transmission through an Optical Fiber.

This article describes characteristics of Nd: YAG lasers and the technologies of beam delivery through flexible optical fibers. The spread of the industrial YAG laser market has been accelerated by the enhancement of laser power and by the utilization of flexible optical fibers for beam delivery. New methods of bothbeam division and beam addition are developed by using fiber beam delivery technologies . Fiber power transmission enables the use of high power YAG lasers for new applications in extremely severe environments such asthe interior. of thin pipes or underwater.

Nonlinear Hanle effect in the active discharge of an argon laser

We present experimental evidence of the NonLinear Hanle Effect (NLHE) on the 488 nm transition in an active discharge of an argon laser. Experimental data are used to estimate the homogeneous linewidth of the upper level of the transition. The role of the NLHE in the laser power enhancement is also discussed.

Anisotropy of dissolution and microrelief of II–VI semiconductor compound surfaces

AbstractThe shape, crystallographic orientation and size of microrelief elements of various surfaces of CdS, ZnSe and ZnO monocrystals after chemical etching have been studied. When illuminated with a focused laser beam, the microrelief creates a symmetric light pattern, or light figures, on the opposite surface whose shape corresponds to the crystal symmetry.The effects of the dissoltion rate and etching time on the form, size and angles of the microrelief elements in the temperature interval from 263 to 333 K were investigated. During etching, laser light was also used to convert the process of selective etching into a polishing process. To elucidate the relationship between the crystallographic orientation of the microrelief elements and the dissolution anisotropy, mean etching rates were determined and polar diagrams of resistance to dissolution were constructed for {1120} and {0001} by the Gross method. The relation between the kinetics of dissolution and the structure of the chemical bonds is discussed.The light figures formed by the surface microrelief enabled us to carry out the approximate orientation of semiconductor planes and solid samples. In the early stages of dissolution one may determine the density and distribution of the microscopic etch pits. The microrelief created on the side surfaces and the ‘fully reflected’ mirrors of II–VI semiconductor lasers pumped by electron beam or optical radiation promote the multiple enhancement of laser power and efficiency.

Flowing gas operation of a planar discharge RF excited CO2 laser

The operation of a planar, transverse radio frequency discharge carbon dioxide laser using slow gas flow is described, with power output up to 430 W. The flow enhancement of laser power is correlated with carbon dioxide dissociation and with axial temperature, measured using an interferometric technique.

Oxide conductive coated cathodes for a sealed-off CO2 laser

Cold cathodes coated with oxide conductive materials, such as indium tin oxide and tin oxide, were applied to dc gas discharges of a sealed-off CO2 laser. Laser power enhancement and stable gas discharge, two areas of laser performance, were affected, in contrast to the uncoated metallic cathode. Mass spectrometric study revealed a correlation of laser power enhancement and an increase in the CO2 content associated with these coated cathodes.

XeCl laser power enhancement with an external ultraviolet laser

Enhancements in the output energy of an XeCl laser of more than 50 percent have been observed by injecting 2-43 mJ of 308 nm laser radiation into the resonator 10-150 ns prior to the emergence of the final XeCl pulse. This effect is a strong function of the time delay ( \Deltat ) between the two lasers and is most pronounced when the injected (external) pulse precedes the XeCl laser pulse by 45 ns. For |\Deltat| \lsim 100 ns, the external radiation appears to be simply seeding the XeCl laser cavity which allows the second laser to reach threshold earlier and thereby improve its extraction efficiency. For 100 \lsim |\Deltat| \lsim 150 ns, the enhancement may to arise from the depletion of the number density of an impurity molecule which absorbs strongly at 308 nm.

Enhancement of laser power at 7588 Å in HeZn hollow cathode laser by the addition of xenon

The effects of inert gas additives on the laser output power in the HeZn hollow cathode laser are investigated. The increase of nearly 50% in the laser power at 7588 Å has been observed when a small amount of xenon was mixed into the HeZn hollow cathode discharge tube. The mechanisms of the enhancement of the 7588 Å laser output by the addition of xenon are discussed.

Characteristics of a CW CO laser resulting from a CS 2-O 2 additive flame

The use of a ribbon burner resulted in a 100 fold laser power enhancement from a CS 2-O 2 free burning flame. The effect of He, SF 6, N 2O, CO, CO 2, N 2, SO 2, and NO 2 on laser power was examined. The highest power, 0.6 W, was achieved from a mixture of CS 2, O 2, and N 2O at flow rates of 3.9, 110, and 7.6 millimoles/sec, respectively.