Optical fiber array for the delivery of high peak-power laser pulses for fluid flow measurements

Fiber delivery of 64.7 mJ laser pulses (approximately 6 ns duration) from a Q-switched Nd:YAG laser operating at 532 nm is demonstrated. A custom diffractive optical element was used to shape the laser beam and facilitate coupling into a linear fiber array. This launch arrangement achieves an improvement in launch efficiency compared with a circular fiber bundle evaluated in previous work and the delivery of higher pulse energies is demonstrated. The bundle is capable of delivering light of sufficient pulse energy and, importantly, with suitable focusability, to generate a thin light sheet for the fluid flow measurement technique of particle image velocimetry (PIV). Fiber delivery offers an advantage, in terms of optical access, for the application of PIV to enclosed measurement volumes, such as the cylinder of a combustion engine.     

Optimal beam size for light delivery to absorption-enhanced tumors buried in biological tissues and effect of multiple-beam delivery: a Monte Carlo study

Optimal laser light delivery into turbid biological tissues was studied by using Monte Carlo simulations based on the delta-scattering technique. The goal was to deliver efficiently the maximum amount of optical power into buried tumors being treated while avoiding potential damage to normal tissue caused by strong optical power deposition underneath the tissue surface illuminated by the laser beam. The buried tumors were considered to have much higher absorption than the surrounding normal tissue because of selective uptake of the absorption-enhancement dye. The power delivering efficiency to buried tumors was investigated for various diameters of the laser beam. An optimal beam diameter was estimated to achieve the maximum product of the power coupling efficiency and the power delivered to the buried tumor. The distribution of power deposition was simulated for single-beam delivery and multiple-beam delivery as well. The simulated results showed that with an appropriate dye enhancement and an optimal laser delivery configuration, a high selectivity for laser treatment of tumor could be achieved.     

Development of a new laser cladding process for manufacturing cutting and stamping dies

An integrated powder delivery system is described, which can provide a highly stable, continuous, and accurate powder feeding rate, and deliver the alloy powders coaxially into the laser-generated molten pool to form high-quality cladding tracks. By combining such a powder feeding system and computer-aided design/computer aided machining system, complex, three-dimensional geometric patterns were deposited on AISI 1045 steel plate or roller via laser cladding for manufacturing cutting and stamping dies, and laminated metal matrix composites. The microstructures of cladding layers, interface, and heat-affected zone were characterized, and the microhardness of a transverse section of single cladding tracks was also measured. © 1998 Chapman & Hall     

Evolution of microstructure in laser clad Fe–Cr–Mn–C alloy

Abstract

The laser surface cladding technique was used to form in situ Fe–Cr–Mn–C alloys on AISI 1016 steel substrate. In this process, mixed powders containing Cr, Mn, and C in the weight ratio 10: 1 : 1 were delivered using a screw feed, gravity flow, carrier gas aided system into the melt pool generated by a 10 kW CO₂ laser. This technique produced an ultrafine microstructure in the clad alloy layer. The microstructure of the laser surface clad region was investigated by optical, scanning and transmission electron microscopy, and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic transformation or retained austenite phase.

MST/356     

The phenomena of the interaction of Nd3+-glass laser light with 6H13 alloy steel

The variation in the physical and chemical structure of the 6H13 alloy steel irradiated by laser light have been investigated. The phenomena of the capillary waves within the power density range (4.3×10⁹<P<13.8×10⁹) watt/m² have been observed and the hydrodynamic parameters of alloy steel have been determinated. The nature of the laser light interaction with metal is discussed in electronmicroscopy and X-rays analysis terms.     

Temperature Criterion of Laser Welding for Joining Aluminum Alloy with Low-Carbon Steel

Aluminum alloy and low-carbon steel are dissimilar metals. In order to obtain a reciprocal comprehensive property in a joint component of aluminum alloy and low-carbon steel, laser welding was used as a novel joining process. Based on the experimental results, the temperature criterion of laser welding for joining of aluminum alloy and low-carbon steel is discussed in this paper.     

激光熔覆添加碳化钨的镍基合金层的组织和硬度研究

为促进激光熔覆在金属材料表面改性中的进一步应用,利用光学显微镜、扫描电镜、显微硬度计和电子探针微区成分分析,研究了Q235钢基体上激光熔覆添加有WC的Ni基合金层的特性及其演变,讨论了熔覆层合金成分和显微硬度的变化规律,力求得到熔覆粉的最佳WC含量.结果表明,当添加WC低于30%(质量分数)时,激光熔覆不出现裂纹;而当WC质量分数增加到30%(质量分数)时,熔覆层平均硬度增加,出现裂纹.在熔覆层中WC完全熔化并溶解,凝固组织主要由枝晶和枝晶间共晶组成,熔覆层呈胞状或条带状快凝亚稳的两相组织.     

疲劳损伤的激光衍射谱面光强检测方法研究

根据表面光反射原理,提出一种非接触,非破坏的间接疲劳损伤检测方法,并用40CrNiMoA和LD5材料进行了拉一压非对称循环疲劳检测。试验结果表明,谱面光强的变化对疲劳损伤是敏感的;利用损伤变量D(K_1)和循环次数N的关系曲线,可以对材料进行疲劳损伤检测并对其疲劳寿命进行预测。     

Characteristics of Laser-Fabricated Metal Structures

Laser-aided direct fabrication technology is developed to produce three-dimensional metal alloy structures directly from the constituent elements. The shapes of the structures are designed using Computer Aided Design (CAD) tools and are fabricated as real parts by fusing powders with a laser beam. In this study, alloy structures of simple plate like geometry were produced by mixing stainless steel (SS 316) powder with either copper or aluminum powder. The thickness of the component is related to the process parameters through an energy balance equation, which is verified against experimental data. Material properties such as hardness, strength and conductivity are analyzed and optical micrographs are presented to exhibit the microstructure of the alloy. The results show improved hardness at certain locations in the alloy, higher thermal conductivity of stainless steel. However, the structures broke due to brittle failure under tensile loads.     

Polyethylene Glycol and Polyethylenimine Dual‐Functionalized Nano‐Graphene Oxide for Photothermally Enhanced Gene Delivery

Graphene oxide (GO) has been extensively explored in nanomedicine for its excellent physiochemical, electrical, and optical properties. Here, polyethylene glycol (PEG) and polyethylenimine (PEI) are covalently conjugated to GO via amide bonds, obtaining a physiologically stable dual‐polymer‐functionalized nano‐GO conjugate (NGO‐PEG‐PEI) with ultra‐small size. Compared with free PEI and the GO‐PEI conjugate without PEGylation, NGO‐PEG‐PEI shows superior gene transfection efficiency without serum interference, as well as reduced cytotoxicity. Utilizing the NIR optical absorbance of NGO, the cellular uptake of NGO‐PEG‐PEI is shown to be enhanced under a low power NIR laser irradiation, owing to the mild photothermal heating that increases the cell membrane permeability without significantly damaging cells. As the results, remarkably enhanced plasmid DNA transfection efficiencies induced by the NIR laser are achieved using NGO‐PEG‐PEI as the light‐responsive gene carrier. More importantly, it is shown that our NGO‐PEG‐PEI is able to deliver small interfering RNA (siRNA) into cells under the control of NIR light, resulting in obvious down‐regulation of the target gene, Polo‐like kinase 1 (Plk1), in the presence of laser irradiation. This study is the first to use photothermally enhanced intracellular trafficking of nanocarriers for light‐controllable gene delivery. This work also encourages further explorations of functionalized nano‐GO as a photocontrollable nanovector for combined photothermal and gene therapies.     

激光增材制造合金钢力学性能超声纵波定量无损评价

目的研究采用超声无损检测方法定量评价激光增材制造合金钢的布氏硬度和抗拉强度。方法通过搭建高精度超声纵波声时测量系统,采用脉冲反射回波法测量不同热处理状态激光增材制造24CrNiMo合金钢标定试件的超声纵波传播声时,计算超声纵波声速;在考虑激光增材制造合金钢各向异性和成形界面对超声纵波传播特性影响的基础上,研究标定试件微观组织对超声纵波声速的影响,建立标定试件激光扫描方向布氏硬度、抗拉强度、微观组织与超声纵波声速之间的映射关系。结果建立了超声纵波评价硬度及抗拉强度的标定模型,并对标定模型预测误差进行验证,硬度及抗拉强度标定模型预测误差均小于10%,满足工程应用误差指标要求。结论采用超声纵波声速可以实现激光增材制造合金钢硬度及抗拉强度的定量评价与表征。     

Feasibility study of a system for combined light dosimetry and interstitial photodynamic treatment of massive tumors

A system for the photodynamic laser treatment of massive tumors that employs multiple optical fibers to be inserted into the tumor mass is described. The light flux through the tumor can be assessed by use of the individual fibers both as transmitters and as receivers. With a computer model that describes the diffusive light propagation, optical dosimetry is under development. The system has been tested in an experimental animal tumor model in preparation for clinical work. Currently, delta-aminolevulinic acid is used as a sensitizer, activated by 635-nm radiation from a 2.0-W compact diode laser system. With the availability of future, highly selective drugs absorbing approximately 750 nm, larger tumor volumes should be treatable, and surrounding, sensitive normal tissue should be spared.     

Semiconductor laser insert with uniform illumination for use in photodynamic therapy

A low-cost semiconductor red laser light delivery system for esophagus cancer treatment is presented. The system is small enough for insertion into the patient's body. Scattering elements with nanoscale particles are used to achieve uniform illumination. The scattering element optimization calculations, with Mie theory, provide scattering and absorption efficiency factors for scattering particles composed of various materials. The possibility of using randomly deformed spheres and composite particles instead of perfect spheres is analyzed using an extension to Mie theory. The measured radiation pattern from a prototype light delivery system fabricated using these design criteria shows reasonable agreement with the theoretically predicted pattern.     

Gap-free fibre laser welding of Zn-coated steel on Al alloy for light-weight automotive applications

As a result of new policies related to global warming announced by the European Union, avoiding unnecessary energy waste and reducing environmental pollution levels are becoming a major issue in the automotive industry. Accordingly, the lap welding of Zn-coated steels process, which is commonly used for producing car doors, has been gradually developed to lap welding of Zn-coated steel to light materials, such as Al alloy, Mg alloy and composite materials, in order to effectively reduce the vehicle weight. In certain part of car manufacture, organic glues are used to temporally join the Zn-coated steels and Al alloys before permanent welding takes place. The stability of such temporary joining by glues needs improving. Laser “stitching” or low strength welding could be considered as an alternative. However, challenges exist in joining Zn-coated steel on Al alloy by laser welding, due to significant differences of material properties between the two welding materials. Porosity, spatter and intermetallic brittle phases are readily produced in the weld. In this study, the effects of welding speed, laser power, number of the welding passes and type of shielding gas in gap-free welding of Zn-coated steel on Al alloy were investigated using a 1 kW single mode continuous wave fibre laser. Results show that a weld with higher shear strengths in the laser stitching application and less intermetallic phases could be obtained when nitrogen gas was used as the shielding gas. The corrosion resistance and the surface finish of the weld could be improved in double pass welding, especially when argon gas was used as the shielding gas.     

Photorefractive Beam splitter for Free-Space Optical Interconnections

A photorefractive beam splitter (PRBS) is introduced as an alternative to a polarizing beam splitter (PBS) for coupling optical power into reflective modulators in a free-space optical interconnection system. The PRBS uses a single diffraction grating recorded in a photorefractive material to redirect the incident laser light into the first diffraction order and onto the modulators. Reflected interconnection light not matching the Bragg angle criteria transmits uncoupled through the beam splitter. Experimental results show that the PRBS provides better, more uniform transmission for off-axis beams than the currently used PBS.     

Automatic alignment-control system for a suspended Fabry-Perot cavity

In interferometric gravitational-wave detectors, most of the optical components are suspended by wires so that they are isolated from all kinds of forces except gravity. The requirement for the alignment of optical components to the laser beam is crucial. We have demonstrated a servo system developed for a Fabry-Perot cavity whose mirrors are suspended independently. We use mechanical modulation and a lock-in detection method to detect any misalignment. This system directly detects the relation between the axis of the laser beam and the axis of the cavity and automatically aligns the cavity to the laser beam. We confirmed that the intensity of the reflected light from the suspended Fabry-Perot cavity can be minimized with this system. Automated control of the alignment of the large-scale detectors is also discussed.     

Fabrication of an aluminum, Caribbean-style, musical pan: Metallurgical and acoustical characterization

We report herein the first development and fabrication of a 6061 aluminum alloy pan and compare its tuning and acoustic spectra for selected notes with a standard low-carbon steel Caribbean pan fabricated from a 210-L barrel. The experimental aluminum alloy pan was completely manufactured by welding a 1.68-mm-thick head sheet to a 9-mm² aluminum alloy hoop, sinking the head by pneumatic hammering and welding a 1.15-mm-thick aluminum alloy side or skirt to the hoop. This experimental pan was 0.66 m in diameter, in contrast to the 210-L steel barrel standard, which had a diameter of 0.57 m. Chromatic tones were observed for most rim notes on the aluminum alloy pan, but the highest octave range notes at the pan bottom were not tuned. Microstructural characterization by light optical metallography and transmission electron microscopy illustrated the necessity for high dislocation densities and associated hardness in order to stabilize the notes and to assure their chromatic tuning.     

激光熔覆镍基合金层的组织与高温耐磨性能

为了改善304不锈钢工件的高温耐磨性能,利用CO2激光器在其表面熔覆了Ni基高温合金层。研究了熔覆层的物相组成、显微组织、成分分布,测试了其显微硬度、高温耐磨性能等,并与基材进行了对比。结果表明:Ni基合金熔覆层的组织从熔池底部到表层为胞状晶—柱状枝晶—树枝晶;熔覆层的主要组成相是Ni3Cr2,NbC,Mo2C与Cr23C6;Ni基合金粉末中添加难熔元素Cr,Mo,Nb等对熔覆层的组织起到了固溶强化、硬质相强化和弥散强化作用;熔覆层的平均显微硬度达到了405 HV,高温耐磨性能是基体的2倍多。     

Programmable color tuning of a multiline laser by means of a twisted nematic liquid crystal display

An optical system useful to tune in a controlled way the color of a triline argon krypton (Ar-Kr) laser by means of a twisted nematic liquid crystal display (TNLCD) is presented. The optical setup employs a 4f system and two blazed gratings to first separate and then recombine the spectrum of the light beam. The TNLCD is included in the intermediate focal plane operating in the amplitude modulation mode to control the relative transmission of each spectral line. The resulting color is accurately predicted by using a previously developed physical model of the spectral and voltage dependence of the TNLCD birefringence. By simply changing the gray level image addressed to the display, the Ar-Kr laser is color modulated at a video rate, thus becoming an interesting, reconfigurable, coherent light source for applications such as multicolor holography or color inspection.     

Erbium:YAG laser lithotripsy by use of a flexible hollow waveguide with an end-scaling cap

An Er:YAG laser light delivery system composed of a polymer-coated silver hollow waveguide and a quartz sealing cap has been developed for calculus fragmentation. Sealing caps with various distal-end geometries were fabricated, and the focusing effects of these caps for Er:YAG laser light were measured both in air and in water. Owing to the high power capability of the quartz a beam of sealing caps, Er:YAG laser light with an output energy of 200 mJ and a repetition rate of 10 Hz was successfully transmitted in saline solution by use of the system. Calculus fragmentation experiments conducted in vitro showed that the delivery system is suitable for medical applications in lithotripsy. We also found that the cap with a focusing effect is more effective in cutting calculi. The deterioration of the sealing caps after calculus fragmentation is also discussed.