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A Fluidic Interface with High Flow Uniformity for Reusable Large Area Resonant Biosensors
摘要： Resonant biosensors are known for their high accuracy and high level of miniaturization. However, their fabrication costs prevent them from being used as disposable sensors and their effective commercial success will depend on their ability to be reused repeatedly. Accordingly, all the parts of the sensor in contact with the ?uid need to tolerate the regenerative process which uses different chemicals (H3PO4, H2SO4 based baths) without degrading the characteristics of the sensor. In this paper, we propose a ?uidic interface that can meet these requirements, and control the liquid ?ow uniformity at the surface of the vibrating area. We study different inlet and outlet channel con?gurations, estimating their performance using numerical simulations based on ?nite element method (FEM). The interfaces were fabricated using wet chemical etching on Si, which has all the desirable characteristics for a reusable biosensor circuit. Using a glass cover, we could observe the circulation of liquid near the active surface, and by using micro-particle image velocimetry (μPIV) on large surface area we could verify experimentally the effectiveness of the different designs and compare with simulation results.
关键词： micro-machining,microengineering,biosensor,?uidic interface,planar ?ow
更新于2025-09-23 15:21:21
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Fabrication of large-scale freestanding THz wire grid polarizers by femtosecond laser micromachining
摘要： High-performance THz polarizers, as a quasi-optical device to manipulate THz waves, are highly demanded for THz spectroscopy and imaging applications. In this work, we have employed the femtosecond laser micro-machining technique to fabricate freestanding THz wire grid polarizers with two kinds of reinforced line structures which weaken the e?ects of gravity sagging and entanglement of long free wires, thus enabling large-scale processing. The e?ect of the reinforced lines on the polarizers were simulated by the Finite-Di?erence Time-Domain (FDTD) method, and the performances of the polarizer were characterized by THz time-domain spectroscopy and compared with that of a commercial wire gird polarizer. The calculated transmittance is in good agreement with the FDTD results. The degree of polarization and the extinction ratio of the polarizer with discontinuous reinforced lines are better than those of a commercial wire grid polarizer.
关键词： Time-domain THz spectroscopy,THz,Femtosecond laser micro-machining,Wire grid polarizer
更新于2025-09-23 15:21:01
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Generation and Characterization of Laser Induced Periodic Surface Structures on Plastic Injection Molds
摘要： In injection molding, high pressure is required to fill the mold, due to the high viscosity of thermoplastic polymers, the reduced thickness of the cavity and the low mold temperature. In this work, we investigate the functionalization of mold cavities for Injection Molding by means of Laser-Induced Periodic Surface Structures (LIPSS) generated on the ground surface of AISI 420 stainless steel through a picosecond laser. The LIPSS formation is examined with reference to the process parameters, highlighting how they affect the generated pattern. The improvements of the functionalized mold surface on the Injection Molding process are experimentally characterized and discussed. In particular, the slipping of molten PET was investigated as a function of nano-structuring orientation and injection velocity. The results demonstrate that LIPSS parallel to flow induce strong wall slip of the polymer melt, allowing a maximum reduction of the injection pressure of 10%.
关键词： Wall slip,Laser micro machining,Injection molding
更新于2025-09-23 15:19:57
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Development of a novel system for in-situ repair of aeroengine airfoil via pulsed laser ablation
摘要： A novel system for performing in-situ micro-machining of aero-engines for repair applications is proposed in this paper. Using Pulsed Laser Ablation (PLA) as material removal technique, surface cracks caused by foreign objects colliding with airfoils are removed by performing a layer-by-layer micro-machining in the area surrounding the damaged zone. Compared to conventional repair performed by micro-grinding, our invasive PLA system demonstrates a similar level of performance, evaluated from the point of view of fatigue strength in the high cycle (> 107) regime. The follow-up fractographic and metallurgical analysis, indicated that although some micro-structural characteristics are different between the repair methods, the incurred surface damage is limited in magnitude to a thin surface layer (< 30 μm) and the influence on fatigue life is comparable. In the last section, a novel prototype system is presented which allows performing the PLA repair in-situ by use of a miniaturized laser scanning head coupled with a flexible mechanical deployment arm. The system has been successfully tested inside a Roll-Royce Trent jet engine; effectively this proves the possibility of performing in-situ laser micro-machining inside complex mechanical systems such as aero-engines, without the need for complex/expensive disassembly.
关键词： Miniaturized laser system,In-situ micro-machining,Pulsed laser ablation,Aeroengines
更新于2025-09-19 17:13:59
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Design and Characterization of Surface Relief Grating on Etched Multimode Optical Fiber For Refractive Index Sensing
摘要： We report a simple and compact optical fiber sensor based on surface relief gratings in conventional graded-index multimode optical fiber (GIMMF) for refractive index sensing. Bragg gratings on MMF are less explored compared to its single mode counterpart, even though the MMF platform possesses several advantages such as robustness, enhanced light-matter interaction and easy light coupling. In this work, surface relief gratings are directly written on one side of the cladding etched MMF core surface by using focused ion beam milling (FIB). A detailed theoretical analysis of the structure and sensing principle is analysed. The device performance as a refractive index sensor has been investigated experimentally by immersing the device in different concentration of NaCl solution. Experimental results show a sensitivity of 70 nm/RIU for a refractive index range of 1.333 to 1.345. The device is easy to fabricate with high repeatability and low cost, compactness in design and competent to be used in harsh environmental conditions. The surface grating on etched MMF provides a better interaction between the sensing region and the environment which makes it a potential candidate for various chemical and biological sensing applications.
关键词： optical fiber sensor,refractive index sensor,Multimode optical fiber grating,optical fiber micro-machining
更新于2025-09-16 10:30:52
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Comparative Experimental Investigation of Micro-channel Fabrication in Ti Alloys by Laser Ablation and Laser-induced Plasma Micro-machining
摘要： Reliable and improved micro-fabrication processes for high-strength alloys are needed due to their increasing use in micro-scale applications. Laser-Induced Plasma Micro-Machining (LIPMM) has been shown to have several advantages over conventional direct laser ablation. In this study micro-channels are fabricated in Ti-6Al-4V, one of the difficult-to-machine materials, to compare the micro-manufacturing capabilities of direct laser ablation to LIPMM. It has been shown that LIPMM results in much deeper channels and higher aspect ratios and better machining consistency than direct laser ablation.
关键词： Micro-Machining,Laser Ablation,Laser-Induced Plasma Micro-Machining (LIPMM),Ti64
更新于2025-09-12 10:27:22
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High Aspect Ratio Microstructuring of Copper Surfaces by Means of Ultrashort Pulse Laser Ablation
摘要： Laser beam machining (LBM) is capable of almost force-free 2D and 3D machining of any kind of material without tool wear. This process is defined by many parameters, such as pulse energy, frequency, scanning velocity and number of scanning repetitions. Modern laser machines provide high energy at shorter pulse durations and have more precise positioning systems than machines of the past. These can easily fulfil today’s continuous changing product requirements. For an overall understanding, an extensive amount of experimentation is required to display the interaction laws and dependencies between process parameters, as well as the resulting shapes and quality of the machined surface. By using an ultrashort pulse (USP) laser, a wide range of customer oriented applications in micrometer scale can be addressed, which leads to precise ablation with minimal thermal damage. This paper provides knowledge on the machining of copper micro features with high aspect ratio and a 532 nm wavelength laser beam. Aspect ratios up to 17 and slot widths smaller than 20 μm were performed with a beam radius ω0 smaller than 5 μm and pulse duration smaller than 12 ps. For desired slot geometries, necessary process parameters were developed and their physical limits are shown and discussed. The limits of minimum structure size have been analysed by observing the remaining material between slots at decreasing distances. Material debris deposits on the non-machined surface, as well as chemical changes of copper, were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). Special attention was given to the taper angle, which arises due to the Gaussian distribution of energy in the laser beam.
关键词： cold laser ablation,micro machining,high aspect ratio
更新于2025-09-12 10:27:22
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Thermal and optical performance characteristics of a spatial light modulator with high average power picosecond laser exposure applied to materials processing applications
摘要： A spatial light modulator (SLM) addressed with Computer Generated Holograms (CGH’s) can create structured light fields when an incident laser beam is diffracted by a phase CGH. The power handling limitations of SLMs based on a liquid crystal layer have always been of some concern. Now, with careful engineering of chip thermal management, we present the detailed optical phase and temperature response of a liquid cooled SLM exposed to picosecond laser average powers up to 220W at 1064nm – new knowledge critical for determining device performance at high laser powers. SLM chip temperature rose linearly with incident laser exposure, increasing by only 5°C at 220W incident power, measured with a thermal imaging camera. Thermal response time with continuous exposure was 1-2 seconds. The optical phase response with incident power approaches 2π radians with average powers up to 130W while above this power, liquid crystal thickness variations limit phase response to just over π radians. These remarkable performance characteristics show that liquid crystal based SLM technology is highly robust when efficiently cooled. High speed, multi-beam plasmonic surface micro-structuring at a coverage rate of 8cm2s-1 is achieved on polished metal surfaces at 25W exposure, while diffractive multi-beam surface ablation on stainless steel at an ablation rate of ～4mm3min-1 is demonstrated with average power 100W. Continuous exposure for many hours exceeding 100W laser power did not result in any detectable drop in diffraction efficiency hence no permanent changes in SLM phase response characteristics have been observed This research work will help to accelerate the use of liquid crystal SLMs for both scientific and ultra-high throughput laser-materials micro-structuring applications.
关键词： Spatial light modulator,active cooling,high average power picosecond laser,high power laser micro-machining
更新于2025-09-12 10:27:22
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Novel strategy for ultrafast pulsed laser micromachining of rotational symmetric metallic parts
摘要： Ultra-fast lasers have already been used to machine rotational symmetric metallic parts for several years but did not prevail against much cheaper fiber lasers. The limiting factor up to now is the dynamics of the rotary and linear axes, that are used to move the part underneath the stationary laser beam. Although the quality of the surface machined with ultrafast pulsed laser radiation is better than that machined with fiber laser radiation, an overall economic consideration mostly did not justify the utilization of ultrafast pulse lasers for this kind of application. Therefore, new and innovative concepts are needed to exploit the potential of ultrafast pulse lasers, in particular high repetition rate and the steadily increasing average power. The realization that will be presented uses a high-end galvanometric scanner to move the laser beam at speeds of several ten meters per second across the constantly rotating part. The most important part is the synchronization of the laser, the scanner and the axes.
关键词： efficiency,ultrafast lasers,laser micro machining,synchronization,galvanometric scanner
更新于2025-09-12 10:27:22