Intensity-based optical fiber sensor for monitoring corrosion of aluminum alloys

A new method, based on the shift of light power transmitted through fiber, to measure corrosion of aluminum is presented. A multimode fiber was metallized by use of physical vacuum to deposit aluminum onto an unclad part of a fiber of 1 to 2 cm length. Scanning-electron microscopy and x-ray diffraction were used to show, the formation and corrosion of the metallized film. The light signal driven by metal corrosion was affected by the film's thickness and the concentration of the corrosive solution of sodium hydroxide.     

Hollow fiber optics with improved durability for high-peak-power pulses of Q-switched Nd:YAG lasers

To improve the damage threshold of hollow optical waveguides for transmitting Q-switched Nd:YAG laser pulses, we optimize the metallization processes for the inner coating of fibers. For silver-coated hollow fiber as the base, second, and third Nd:YAG lasers, drying silver films at a moderate temperature and with inert gas flow is found to be effective. By using this drying process, the resistance to high-peak-power optical pulse radiation is drastically improved for fibers fabricated with and without the sensitizing process. The maximum peak power transmitted in the fiber is greater than 20 MW. To improve the energy threshold of aluminum-coated hollow fibers for the fourth and fifth harmonics of Nd:YAG lasers, a thin silver film is added between the aluminum film and the glass substrate to increase adhesion of the aluminum coating. By using this primer layer, the power threshold improves to 3 MW for the fourth harmonics of a Q-switched Nd:YAG laser light.     

Fabrication of copper oxide-coated hollow waveguides for CO2 laser radiation

Hollow fibers for transmitting CO(2) laser light were fabricated by the chemical vapor deposition (CVD) method. A dielectric film of copper oxide (Cu(2)O) was deposited upon the inside of a Ag-coated glass capillary by use of a metal acetylacetonate as the precursor. The waveguide, which was coated with Cu(2)O and had a bore diameter of 700 mum, showed a loss of 0.9 dB/m for CO(2) laser light. The Cu(2)O film deposited by CVD had high chemical and heat resistivity. Therefore a hollow fiber coated with copper oxide is suitable for high-power laser applications in a severe environment.     

Aluminum–GFRP hybrid square tube beam reinforced by a thin composite skin layer

Ultimate bending moments and energy-absorption capability of aluminum–glass fiber reinforced plastic (GFRP) hybrid tube beams were experimentally analyzed with particular focuses on effects of thin GFRP skin layer in relation to bending deformation behavior and fracture characteristics. Various hybrid tube beams were fabricated by inserting adhesive film between prepreg and metal layers and by aligning various composite ply angles. Under 3-point bending loads, aluminum–GFRP hybrid tube beams showed characteristic fracture processes according to the lay-up kinds of the skin layer in comparison to the virgin aluminum tube beams. In particular, the hybrid tube beams having a 0.5 mm thick [0°/90°]_s skin layer showed the largest improvement in specific maximum moment (about 67%) and in specific energy-absorption (29%). Consequently, there was an optimal thickness and lay-up of the composite skin layer in creating the best performance of the hybrid tubes.     

Optimization study of the femtosecond laser-induced forward-transfer process with thin aluminum films

The parameters for an effective laser-induced forward-transfer (LIFT) process of aluminum thin films using a femtosecond laser are studied. Deposited feature size as a function of laser fluence, donor film thickness, quality of focus, and the pulse duration are varied, providing a metric of the most desirable conditions for femtosecond LIFT with thin aluminum films.     

Oxide thickness measurements by infrared ellipsometry

Current interest' in anodized aluminum surfaces as substrates for adhesive bonding has created a need to measure the properties of the oxide layer in a non-contacting manner. Visible light ellipsometry is a very sensitive non-contacting technique for measuring the thickness of very thin films on smooth surfaces whose optical constants are known. However, the method is limited to film thicknesses which are generally less than 2000 Å and validity is lost when there is appreciable scattering caused by the roughness of the substrate and the structure of the oxide itself. These objections become much less severe if the operating wavelength is in the infrared region. Such an infrared ellipsometer has been developed to measure the thickness of oxides produced by anodization of aluminum with production-finished surfaces. The instrument operates with a 10.6 μm beam from a low power CO₂ laser and uses a 6328 Å beam from a He-Ne laser for alignment and location of the measurement region. The oxides were formed on unclad 7075 aluminum by anodization in an ammonium pentaborate solution at constant current to termination voltages of from 25 to 275 V in 25 V increments. The measured ellipsometric quantities Δ and ψ were used to compute the corresponding metal oxide film thicknesses using a complex refractive index N = 2.39?i41.36 for the substrate. The results for a film refractive index of 1.50 were in close agreement with those measured with a scanning electron microscope. Elemental concentration profiles for each surface were made by Auger electron spectroscopy.     

Pure antimony film as saturable absorber for Q-switched erbium-doped fiber laser

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of Sb on a polyvinyl alcohol (PVA) film through physical vapour deposition (PVD) process. A 1 × 1 mm area of the film SA is cut and integrated into between two fiber ferrules inside the laser cavity for intra-cavity loss modulation. Self-starting and stable Q-switched pulses are obtained within a pump power range from 60 to 142 mW. Within this range, the repetition rate increases from 70.82 to 98.04 kHz, while pulse width decreases from 7.42 to 5.36 μs. The fundamental frequency signal-to-noise ratio of the pulse signal is 74 dB, which indicates the excellent stability of the pulses. The maximum output power and pulse energy are 8.45 mW and 86.19 nJ, respectively. Our demonstration shows that Sb film SA capable of generating stable pulses train operating at 1.55-micron region.     

Surface Plasmon Resonance-Laser Desorption/Ionization-Time-of-Flight Mass Spectrometry

The laser desorption/ionization (LDI) process is investigated under surface plasmon resonance (SPR) conditions using time-of-flight mass spectrometry (TOFMS). We demonstrate that LDI-TOFMS at the SPR angle requires a lower minimum laser fluence for the production of silver monomer and cluster cations from ablation of a thin silver film substrate. In the LDI of gramicidin S deposited on a thin silver film substrate, the largest intensity for the molecular cation peak occurs when the laser light is incident on the substrate at a specific SPR angle. These results fully confirm SPR enhancement of the LDI process. The capability to perform SPR-LDI on a larger molecular weight analyte (1141 amu for gramicidin S) represents a new milestone beyond the previous achievement with rhodamine B (479 amu). A better understanding of the SPR mechanism is gained with respect to the substrate metals (silver vs aluminum), desorption (microscopic vs mesoscopic), and ionization (chemical vs multiphoton). These findings may be useful in the future design of SPR-LDI techniques for better TOFMS analysis of higher mass biomolecules.     

Structural Characterization of Laser Bonded Sapphire Wafers Using a Titanium Absorber Thin Film

Two sapphire substrates were tightly bonded by irradiation with a 1064 nm nanosecond laser and using a sputtered 50 nm-titanium thin film as an absorbing medium.Upon laser irradiation,aluminum from the upper substrate is incorporated into the thin film,forming Ti-Al-O compounds.While the irradiated region becomes transparent,the bond quality was evaluated by scanning acoustic microscopy.     

Micropatterning: Ultrafast Large‐Area Micropattern Generation in Nonabsorbing Polymer Thin Films by Pulsed Laser Diffraction (Small 6/2011)

An ultrafast, parallel, and beyond‐the‐master micropatterning technique for ultrathin (30?400 nm) nonabsorbing polymer films by diffraction of laser light through a 2D periodic aperture is reported. The redistribution of laser energy absorbed by the substrate causes self‐organization of polymer thin films in the form of wrinklelike surface relief structures caused by localized melting and freezing of the thin film. Unlike conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre‐ablative process without loss of material, and without absorption/reaction with incident radiation. Self‐organization in the thin polymer film, aided by the diffraction pattern, produces microstructures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size, and geometry, and by changing the diffraction pattern.     

Ultrafast large-area micropattern generation in nonabsorbing polymer thin films by pulsed laser diffraction

An ultrafast, parallel, and beyond-the-master micropatterning technique for ultrathin (30-400 nm) nonabsorbing polymer films by diffraction of laser light through a 2D periodic aperture is reported. The redistribution of laser energy absorbed by the substrate causes self-organization of polymer thin films in the form of wrinklelike surface relief structures caused by localized melting and freezing of the thin film. Unlike conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre-ablative process without loss of material, and without absorption/reaction with incident radiation. Self-organization in the thin polymer film, aided by the diffraction pattern, produces microstructures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size, and geometry, and by changing the diffraction pattern.     

Bistability of a self-standing film caused by photothermal displacement

We report on the bistability of a self-standing thin film caused by photothermal displacement. The sample consisted of a self-standing thin film placed in front of a mirror. By irradiating the self-standing thin film with continuous wave laser light, the self-standing thin film deflected with thermoelastic bending moment. Since a standing wave of the laser light was generated by the reflection of the mirror, the bending moment generated on the film was periodic along the optical axis. The displacement of the film was found to be bistable with the laser light intensity. Simultaneously, the light intensity reflected from the sample was also bistable. These phenomena are explained by the photothermal displacement of thin film in the standing wave of laser light.     

Spatial patterning of colloidal nanoparticle-based thin film by a combinative technique of layer-by-layer self-assembly and lithography

A novel approach to generating clear patterns of different types of nanoparticles is presented in this paper. Nanoassembly in the vertical direction was combined with planar micropatterning. This provides industrial applications of a popular layer-by-layer method to produce multilayers of polymers, nanoparticles, and proteins organized on the nanometer scale. A thin film of organic polystyrene spheres was first coated on the pretreated silicon wafer with layer-by-layer self-assembly. Then a layer of aluminium was deposited on the thin film. A layer of positive photoresist was spun on the surface of aluminum and then illuminated with UV light. The exposed parts of the resist were removed and windows were opened above the aluminum. The subsequent etching removed exposed aluminium and left a polystyrene thin film in the open windows. Oxygen plasma was employed to remove the polystyrene thin film on the bottom. Eventually, aluminum and photoresist were removed and only the desired pattern remained. This approach was also employed for the patterning of the silica nanoparticle thin film, a widely used material in various applications. In this case, wet etching was demonstrated to etch silica particles. A scanning electron microscope was used to produce the image of the pattern.     

Mass by energy loss quantitation as a practical submicrogram balance

A simple device integrating a thin film support and a standard microcentrifuge tube can be used for making solutions of accurately known concentration of any organic compound in a single step, avoiding serial dilution and the use of microgram balances. Nanogram to microgram quantities of organic material deposited on the thin film are quantified by ion energy loss and transferred to the microcentrifuge tube with high recovery.     

包覆吸水性材料椭圆管式间接蒸发冷却器的理论与实验研究

从吸水性材料、换热器结构及布水方式入手,设计了采用功能性纤维套、铝箔椭圆管和间歇性供水方式等强化换热措施的间接蒸发冷却器结构。功能性纤维套采用异形涤纶和Lanseal纤维混纺而成,大大加强了水膜导热和水膜表面的蒸发能力;间歇性供水方式保证了管外纤维套凹坑及纤维凹槽不会被水膜堵塞,提供了足够的换热面积;使用铝箔椭圆管并对排列的几何参数进行优化设计,使间接蒸发冷却器的换热性能达到最优化。实验结果表明这种新型管式间接蒸发冷却器和板式间接蒸发冷却器有相近的换热效率E,但阻力明显小于板式。     

A comparison of Schottky barrier position-sensitive detectors as a function of light wavelength

Position-sensitive detectors (PSDs), are single continuous optical sensors that utilize the lateral photovoltaic effect to produce an electrical output that varies linearly with light spot position. This work reports further on the results from Schottky barrier PSDs fabricated from thin films of tantalum, titanium, and aluminum. The optimal thickness of the Schottky metals was determined, trading off light transmissivity and proper Schottky barrier formation. The objective of this work was to determine if devices performed particularly well or poorly under certain light sources and, if so, at what thickness of film. Each device has been tested in one dimension under 5 mW of red laser light, focused broad-band light, as well as filtered red, green, and blue light. It was found that all devices generally responded well to the filtered red light and worst under the green light source. The extent to which this is true depends on the Schottky metal used and its thickness. It was also found that the detector response changed over time. Most interestingly, the tantalum Schottky barrier devices either improved or remained the same while the titanium devices deteriorated noticeably.     

Study of the Electron–Phonon Relaxation in Thin Metal Films Using Transient Thermoreflectance Technique

Electron–phonon (e–ph) relaxation in thin metal films is an important consideration in many ultra-small and ultra-fast applications. In this work, e–ph relaxation in thin gold and aluminum films has been studied using the transient thermoreflectance technique which is demonstrated sensitive enough to study the relaxation process. The optical properties of the thin metal films are different from those of bulk metal and have been measured. Based on confirmation of the measurements, the effects of metal type, film thickness, and interface on e–ph relaxation have been experimentally studied. The thermoreflectance traces of gold and aluminum films have been compared. The results show that the e–ph relaxation and the effect of electron and lattice temperatures on the thermoreflectance of gold and aluminum are quite different. The e–ph relaxation is independent of film thickness and interface.     

Ultraviolet surface plasmon-coupled emission using thin aluminum films

Surface plasmon-coupled emission (SPCE) is the directional radiation of light into a substrate due to excited fluorophores above a thin metal film. To date, SPCE has only been observed with visible wavelengths using silver or gold films. We now show that SPCE can be observed in the ultraviolet region of the spectrum using thin (20 nm) aluminum films. We observed directional emission in a quartz substrate from the DNA base analogue 2-aminopurine (2-AP). The SPCE radiation occurs within a narrow angle at 59 degrees from the normal to the hemicylindrical prism. The excitation conditions precluded the creation of surface plasmons by the incident light. The directional emission at 59 degrees is almost completely p-polarized, consistent with its origin from surface plasmons due to coupling of excited 2-AP with the aluminum. The emission spectra and lifetimes of the SPCE are those characteristic of 2-AP. Different emission wavelengths radiate at slightly different angles on the prism providing intrinsic spectral resolution from the aluminum film. These results indicate that SPCE can be used with numerous UV-absorbing fluorophores, suggesting biochemical applications with simultaneous surface plasmon resonance and SPCE binding assays.     

Hollow fibers for delivery of harmonic pulses of Q-switched Nd:YAG lasers

Flexible hollow fibers for delivery of the second, third, and fourth harmonic pulses of Q-switched Nd:YAG lasers are introduced. For the doubled (532-nm) wavelength, we fabricated a hollow fiber with an internal metal and polymer film by using a silver-mirror plating and a liquid-phase-coating method. For tripled (355-nm) and quadrupled (266-nm) Nd:YAG in the ultraviolet region, we fabricated aluminum hollow fibers with or without an internal polymer layer by using the metal-organic chemical-vapor deposition method. Both types of fiber show high stability for the transmission of high-peak power laser pulses with low transmission losses.     

Role of surface profiles in surface plasmon-polariton-mediated emission of light through a thin metal film

We show that the emission of light mediated by surface plasmon-polaritons through a thin metal film depends sensitively on the profile of the grating structure used to couple the surface plasmon-polariton modes to light. In particular, we show that when the emission of light takes place through a metal film, a non-conformal geometry for the two surfaces of the metal film is to be preferred. Our results may be important in the design of devices such as organic light-emitting diodes.