The second fusion of laser and aerospace-an inspiration for high energy lasers

Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.

Laser‑Induced and MOF‑Derived Metal Oxide/Carbon Composite for Synergistically Improved Ethanol Sensing at Room temperature

Advancements in sensor technology have significantly enhanced atmospheric monitoring.Notably,metal oxide and carbon(MO_(x)/C)hybrids have gained attention for their exceptional sensitivity and room-temperature sensing performance.However,previous methods of synthesizing MO_(x)/C composites suffer from problems,including inhomogeneity,aggregation,and challenges in micropatterning.Herein,we introduce a refined method that employs a metal–organic framework(MOF)as a precursor combined with direct laser writing.The inherent structure of MOFs ensures a uniform distribution of metal ions and organic linkers,yielding homogeneous MO_(x)/C structures.The laser processing facilitates precise micropatterning(<2μm,comparable to typical photolithography)of the MO_(x)/C crystals.The optimized MOF-derived MO_(x)/C sensor rapidly detected ethanol gas even at room temperature(105 and 18 s for response and recovery,respectively),with a broad range of sensing performance from 170 to 3,400 ppm and a high response value of up to 3,500%.Additionally,this sensor exhibited enhanced stability and thermal resilience compared to previous MOF-based counterparts.This research opens up promising avenues for practical applications in MOF-derived sensing devices.

Study on the Effects of Helium-Argon Gas Mixture on the Laser Welding Performance of High Temperature Alloys

In order to solve the problem of porosity in laser deep penetration welding of GH3625 high-temperature alloy plates,five different ratios of high-purity helium gas and high-purity argon gas mixed gases were compared in welding experiments after various process parameter improvements and adjustments failed to achieve Class I welds.The experimental results show that using high-purity helium gas or a mixture of 50%high-purity helium gas and 50%high-purity argon gas can both achieve Class I welds.This indicates that using high-purity helium gas or an appropriate mixed gas instead of pure argon is one of the effective ways to solve the problem of porosity in laser deep penetration welding of high-temperature alloys.The mixture of 50%high-purity argon gas and 50%high-purity helium gas can reduce the consumption of high-purity helium gas,lower production costs,and is more suitable.

The Characteristics of Glued Tensile Shear Strength Constituted of Wood Cut by CO_(2) Laser

The performance of engineered wood products is highly associated with proper bonding and an efficient cutting method.This paper investigates the influence of CO_(2) laser cutting on the wetting properties,the modified che-mical component of the laser-cut surface,and the strength and adhesive penetration near the bondline.Beech-wood is cut by the laser with varying processing parameters,cutting speeds,gas pressures,and focal point positions.The laser-cut samples were divided into two groups,sanded and non-sanded samples.Polyvinyl acetate adhesive(PVAc)was used to bond the groups of laser-cut samples.After assembly with cold pressing,the tensile shear test was carried out.Numerical modelling was carried out to determine the partial elongation and shear strain of the glue line.Based on this,the shear modulus and linear elasticity of the glue line were estimated.Scan-ning electron microscopy was used to assess the adhesive penetration into the porosity structure of the laser-cut samples,and the depth of the heat-affected zone.The laser-cut surface was analysed by Fourier transform infrared spectroscopy.The wetting properties of the laser-cut surface were investigated by using a contact angle goni-ometer.The numerical model of the strain-stress curve confirmed the experimental model.The highest modulus of the linear elasticity of the glue in the numerical calculation belongs to the joint containing laser-cut samples at a gas pressure of 21(bar).The penetration depth of PVAc adhesive into the porosity structure of the laser-cut sam-ples was similar to that of sawn samples.The deepest heat-affected zone in the laser-cut samples was 150µm.A PVAc drop disappeared immediately on the laser-cut surface without sanding,but gradually on the sanded surface.In contrast,the drop on the sawn surface remained with an angle of 32°–48°.The degradation of hemi-cellulose and lignin was proven by the lower intensity of the C=O and C-O Bonds,compared to the sawn surface.

Study on the Two-Dimensional Density Distribution for Gas Plasmas Driven by Laser Pulse

We perform an experimental study of two-dimensional（2D） electron density profiles of the laser-induced plasma plumes in air by ordinarily laboratorial interferometry. The electron density distributions measured show a feature of hollow core. To illustrate the feature, we present a theoretical investigation by using dynamics analysis. In the simulation, the propagation of laser pulse with the evolution of electron density is utilized to evaluate ionization of air target for the plasma-formation stage. In the plasma-expansion stage, a simple adiabatic fluid dynamics is used to calculate the evolution of plasma outward expansion. The simulations show good agreements with experimental results, and demonstrate an effective way of determining 2D density profiles of the laser-induced plasma plume in gas.

Experimental study on gas production and solution composition during the interaction of femtosecond laser pulse and liquid

The process of ionizing normal saline induced by femtosecond laser is studied from the perspective of gas production rate and composition.When the repetition rate is less than 1000 Hz,each laser pulse independently generates ionization gas.At the same time,we discovered the inhibitory effect of meglumini diatrizoici on the ionization process and explained the reasons for this inhibition.Finally,the gas composition proved that the primary gas production mechanism of the femtosecond laser is the decomposition of water molecular,and the composition of the solution after the reaction proved the decomposition effect of the laser on meglumine.

Experimental study on gas metal arc welding and laser hybrid welding of WYS700 steel

Gas metal arc welding, laser welding, and laser-metal active gas welding(MAG) hybrid welding methods were applied to WYS700 steel.Different welding procedures were performed and different welding technologies were compared.Macro metallographs of the welded joints were obtained, and the mechanical properties(such as tensile strength, bending property, and hardness) of the joints formed using the different welding technologies were determined.The results revealed that the joint of the WYS700 steel could be formed well through gas metal arc welding, laser welding, and laser-MAG hybrid welding.Furthermore, the softening of the welding heat affected zone can be effectively reduced to obtain good strength and plasticity by using a suitable welding procedure.Laser-MAG hybrid welding allows the realization of high efficiency and deep penetration for the welding of thick plates with specifications above 3 mm.

Comparative Study on Microstructures of Zincalume Steel(G550)Welded Joint Between Metal Inert Gas and Laser Beam Welding

Zincalume steel(G550)is commonly used in various construction fields because of its high corrosion resistance and good mechanical properties.In recent years,a number of steel companies have massively produced zincalume steel(G550)with large volumes of waste.For the reduction of massive industrial wastes,the zincalume steel(G550)was welded in the lap joint configuration using different welding parameters in the metal inert gas(MIG)welding and laser beam welding(LBW)process in this study.The MIG welding and LBW are more welcomed welding methods due to their high efficiency and low cost.However,they are different as the LBW offers welding speed three to five times faster than MIG welding,while LBW’s heat transfer to workpieces is much less than MIG welding,which can avoid some distortions.The microstructure of zincalume steel(G550)was investigated using scanning electron microscopy(SEM)and the microstructure characterizations of welded specimens were analyzed.The experiment found the columnar dendrites extended under the heat flow direction during the MIG welding and LBW process.Thus,the columnar grains were formed in between the equiaxed zone and fusion zone(FZ)at high heat input and slow cooling rate.Moreover,the grain size of FZ was comparatively smaller than heat affected zone(HAZ)and base metal(BM).

Final Status of a Metal Sample Surface after Multipulse Laser Irradiation in an Ambient Gas

We have investigated the role of the ambient gas nature and pressure in the structure and appearance of the laser treated zone. and the influence of the total duration and temporal shape of laser pulse with the laser tight being λ= 10.6μm wavelength incident upon a metallic surface at intermediate taser intensities of 107-108 W / cm2. A plasma is accompanied by the action of the laser pulse, It acts as an active moderator among laser beam and target thus determining the final status of the contact surface

Experimental Study of Buffer Gas Flow Rate Effect on Output Power of a Copper Vapor Laser

A copper vapor laser with active medium length of 60 cm and bore of 16 mm has been operated and optimized using different buffer gases to investigate the effect of the gas flow rates on the output power. It is found that there is a special optimum gas flow rate associated with the type of buffer gas.

Broad gain,continuous-wave operation of InP-based quantum cascade laser atλ~11.8μm

We demonstrate a broad gain,continuous-wave(CW)operation InP-based quantum cascade laser(QCL)emitting at 11.8μm with a modified dual-upper-state(DAU)and diagonal transition active region design.A 3 mm cavity length,16.5μm average ridge wide QCL with high-reflection(HR)coatings demonstrates a maximum peak power of 1.07 W at 283 K and CW output power of 60 m W at 293 K.The device also shows a broad and dual-frequency lasing spectrum in pulsed mode and a maximum average power of 258.6 mW at 283 K.Moreover,the full width at half maximum(FWHM)of the electroluminescent spectrum measured at subthreshold current is 2.37μm,which indicates a broad gain spectrum of the materials.The tuning range of 1.38μm is obtained by a grating-coupled external cavity(EC)Littrow configuration,which is beneficial for gas detection.

Spectroscopy system based on a single quantum cascade laser for simultaneous detection of CO and CO_2

A quantum cascade laser（QCL） based system for simultaneous detection of CO and CO_2 is developed.The QCL can scan over two neighboring CO（2055.40 cm^（-1）） and CO_2（2055.16 cm^（-1）） lines with a single current scan.The wavelength modulation spectroscopy（ f = 20 k Hz） is utilized to enhance the signal-to-noise ratio.A white cell with an effective optical path length of 74 m is used.The calibration of the sensor is performed and minimum detection limits of 1.3 ppb（1 × 10^（-9））for CO and 0.44 ppm（1 × 10^（-6）） for CO_2 are achieved.

Underwater gas self-transportation along femtosecond laser-written open superhydrophobic surface microchannels(<100μm)for bubble/gas manipulation

Underwater transportation of bubbles and gases has essential applications in manipulating and using gas,but achieving this function at the microscopic level remains a significant challenge.Here,we report a strategy to self-transport gas in water along a laser-induced open superhydrophobic microchannel with a width less than 100μm.The femtosecond laser can directly write superhydrophobic and underwater superaerophilic microgrooves on the polytetrafluoroethylene(PTFE)surfaces.In water,the single laser-induced microgroove and water medium generate a hollow microchannel.When the microchannel connects two superhydrophobic regions in water,the gas spontaneously travels from the small region to the large area along this hollow microchannel.Gas self-transportation can be extended to laser-drilled microholes through a thin PTFE sheet,which can even achieve anti-buoyancy unidirectional penetration.The gas can overcome the bubble’s buoyance and spontaneously travel downward.The Laplace pressure difference drives the processes of spontaneous gas transportation and unidirectional bubble passage.We believe the property of gas self-transportation in the femtosecond laser-structured open superhydrophobic and underwater superaerophilic microgrooves/microholes has significant potential applications related to manipulating underwater gas.

Effect of shielding gas and defocusing on porosity during laser beam welding of 7A52 alloy

Laser beam welding is used to fabricate the 7A52 aluminum alloy plates.Effects of shielding gas and defocusing on porosities are investigated.Porosities are divided into hydrogen porosities and keyhole-induced porosities.With the increasing flow rate of the front shielding gas,the porosity ratio firstly decreases,then increases.The porosity ratio is lowest under the flow rate of 25 L/min.When the flow rate is 30 L/min,the porosity ratio is higher because the large flow rate can affect the stability of the keyhole.The porosity ratio is also higher when the flow rate is less than 25 L/min because the protection is weakened.With the increase of the defocusing,the porosity ratio firstly decreases,then increases.When the defocusing is-2 mm,the porosity ratio is lowest.When the defocusing is more than 0 mm or less than-4 mm,the porosity ratio is higher due to the movement of the instable keyhole.

Pushing the boundaries of diode-pumped solid-state lasers for high-energy applications

We report on the successful demonstration of a 150 J nanosecond pulsed cryogenic gas cooled,diode-pumped multi-slab Yb:YAG laser operating at 1 Hz.To the best of our knowledge,this is the highest energy ever recorded for a diodepumped laser system.

Paired eye-control study of unilateral opaque bubble layer in femtosecond laser assisted laser in situ keratomileusis

AIM: To investigate the predictive factors of the opaque bubble layer(OBL) compared to the fellow eye of same patients in FS200 femtosecond laser assisted laser in situ keratomileusis(FS-LASIK).METHODS: This study consisted of 60 consecutive patients(120 eyes) with unilateral OBL during FS-LASIK. Eyes were divided into OBL(the OBL eyes) and OBL-free groups(the fellow eyes) based on the occurrence of OBL. The preoperative demographic data, refraction, keratometry, corneal astigmatism, pachymetry, intraocular pressure and intraoperative data including the outlet location of gas diffusing canal were collected. Conditional logistic regression analysis was performed to find the associated factors with OBL in the two groups by determining odds ratios(OR) and 95%CI.RESULTS: The preoperative demographic data, mean spherical errors, mean K value, suction time, intraocular pressure and central cornea thickness were not significantly different between the two groups. The outlet location of gas diffusing canal(P<0.01, OR 7.16, 95%CI 2.53-20.32) and the corneal astigmatism(P=0.013, OR 0.13, 95%CI 0.03-0.65) were significantly associated with the incidence of OBL by multivariate logistic regression analysis. Visual acuity, efficacy, and safety were comparable between the two groups two months after surgery except for a slightly lower predictability value for the hard OBL eyes.CONCLUSION: The reduction of the incidence of OBL is obvious when the outlet of gas diffusing canal located at the posterior border of the corneoscleral limbus. This is probably consequent to more effectiveness of gas diffusing canal. Corneal astigmatism is also an independent protective factor for OBL formation.

EVOLUTION OF MICROSTRUCTURE OF LASER SURFACE ALLOYING OF γ TiAi ALLOY WITH NITROGEN

Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.

Incidence and predisposing factors of anterior chamber gas bubbles during femtosecond laser flap creation

AIM:To investigate the incidence and the predisposing factors of anterior chamber(AC)gas bubbles during femtosecond laser(FS)flap creation for laser in situ keratomileusis(LASIK).METHODS:All patients who underwent FS-LASIK surgery at CMU LASIK Center between January 2013 and May 2016 were retrospective reviewed.Preoperative and intraoperative data including keratometry,white-towhite(WTW)corneal diameter,flap parameters(diameter,thickness,hinge position,and tunnel length)and pulse energy were reviewed and compared between incident group and control group.To determine the risk factors,univariate and multivariate conditional logistic regression were used;the eye was unit of analysis.RESULTS:The incidence of AC gas bubbles was 1.6%(22 out of 1378 eyes).The median WTW in the AC bubbles group was 11.5 mm(range 11.1-12.1),which was significantly different from the control group(11.7 mm,range 10.5-12.8,P=0.021).The result of the median WTW minus the flap diameter in the AC bubbles group was 2.5 mm(range 2.1-3.2),which was statistically different to the control group(2.7 mm,range 1.5-3.8,P=0.008).The logistic regression analysis showed that the result of the WTW minus the flap diameter in the AC bubbles group had an adjusted odds ratio of 0.204(95%CI;0.056-0.747,P=0.016).CONCLUSION:Development of AC gas bubbles during FS flap creation is not an uncommon event in Asian eyes which typically have a small WTW.The flap diameter when adjusted relatively to the WTW is a predisposing factor to the possibility of AC gas bubbles occurrence.

Effect of Laser Beam Welding Parameters on Microstructure and Properties of Duplex Stainless Steel

The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.

Influence of Carrier Gas on Analysis of MgO Powders by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） has been widely adopted for the direct multi-elemental analysis with high sensitivity. Especially analysis of fine ceramics by LA-ICP-MS without time-consuming sample decomposition process has been one of the most expecting application field. Small additive elements in MgO powders were analyzed by LA-ICP-MS. For precise and accurate analysis influence of carrier gas （Ar or He） was presented by the signal intensities of ICP-MS, relative standard deviation of signal intensities and ablated particle size distribution. Ablated particles were collected and analyzed by scanning electron microscopy （SEM） to investigate the particle size distribution, and the ablated sample surface was examined by camscope. In He gas atmosphere, the signal was more stable than in Ar gas atmosphere. The signal intensity was higher in Ar than in He. Examination of ablated particles and sample surface reveals that more particles were generated in Ar atmosphere and the distribution of particle size was larger.