Laser-machined fibers as Fabry-Perot pressure sensors

Cavities have been laser ablated in the ends of single-mode optical fibers and sealed by aluminized polycarbonate diaphragms to produce Fabry-Perot pressure sensors. Both conventional fibers and novel, multicore fibers were used, demonstrating the possibility of producing compact arrays of sensors and multiple sensors on an individual fiber 125 microm in diameter. This high spatial resolution can be combined with high temporal resolution by simultaneously interrogating the sensors by using separate laser sources at three wavelengths. Shock tube tests showed a sensor response time of 3 micros to a step increase in pressure.     

Preparation of Fiber Optics for the Delivery of High-Energy High-Beam-Quality Nd:YAG Laser Pulses

Recent improvements in design have made it possible to build Nd:YAG lasers with both high pulse energy and high beam quality. These lasers are particularly suited for percussion drilling of holes of as much as 1-mm diameter thick (a few millimeters) metal parts. An example application is the production of cooling holes in aeroengine components for which 1-ms duration, 30-J energy laser pulses produce holes of sufficient quality much more efficiently than with a laser trepanning process. Fiber optic delivery of the laser beam would be advantageous, particularly when one is processing complex three-dimensional structures. However, lasers for percussion drilling are available only with conventional bulk-optic beam delivery because of laser-induced damage problems with the small-diameter (approximately 200-400-mum) fibers that would be required for preserving necessary beam quality. We report measurements of beam degradation in step-index optical fibers with an input beam quality corresponding to an M(2) of 22. We then show that the laser-induced damage threshold of 400-mum core-diameter optical fibers can be increased significantly by a CO(2) laser treatment step following the mechanical polishing routine. This increase in laser-induced damage threshold is sufficient to propagate 25-J, 1-ms laser pulses with a 400-mum core-diameter optical fiber and an output M(2) of 31.     

Simultaneous machining of parallel grooves in SnO(2) thin films using a Nd:YAG laser and a kinoform

A kinoform is used to split the beam of a Nd:YAG laser into six beams. The laser beams are, by means of optical fibers and collimating-focusing optics, transferred to the surface to be machined. Thus multiple grooves can be machined simultaneously. For demonstration, 100-μm-wide grooves are simultaneously machined into a SnO(2) thin film deposited on a glass substrate. The resulting grooves are well isolated. This result shows that the technique could be used, for example, in solar cell manufacturing to increase the efficiency of laser scribing.     

Optical detection of honeybees by use of wing-beat modulation of scattered laser light for locating explosives and land mines

An instrument is demonstrated that can be used for optical detection of honeybees in a cluttered environment. The instrument uses a continuous-wave diode laser with a center wavelength of 808 nm and an output power of 28 mW as the laser transmitter source. Light scattered from moving honeybee wings will produce an intensity-modulated signal at a characteristic wing-beat frequency (170-270 Hz) that can be used to detect the honeybees against a cluttered background. The optical detection of honeybees has application in the biological detection of land mines and explosives, as was recently demonstrated.     

固体超强酸于多孔高硅氧纤维的负载及其在酯化中的应用

以溶胶浸渍法,将SO42-/ZrO2固体超强酸负载到由酸沥滤工艺制备的多孔高硅氧纤维上,并用于催化合成乙酸正丁酯。研究结果表明,该催化剂具有用量少,酯收率较高,产物易于分离等优点;而且使用寿命长,重复用于5次合成后,酯化率仍高于70%。     

基于离心纺丝技术制备稳定的碳化锆纤维

本研究提出了一种利用离心纺丝技术制备稳定碳化锆(ZrC)纤维的有效方法。此方法使用醋酸锆和蔗糖作为锆源和碳源, 聚乙烯吡咯烷酮(PVP)作为纺丝助剂, 经过1600 ℃的裂解与碳热还原热处理后, 所纺原丝转化成由均匀纳米ZrC晶体组成的ZrC纤维。研究结果表明, 纤维中残留的少量碳可助力ZrC纤维在2000 ℃的超高温环境下仍保持较好的结构稳定性。     

Organic acids on the fabrication of sol-gel lead zirconate titanate fibers

Lead zirconate titanate (PZT, 53/47) fibers are prepared by sol-gel method using organic acids - acrylic and methacrylic acid - to modify the precursors. The macroscopic properties, molecular structure, crystallization behaviour and microstructure of the fibers are investigated as a function of the content and type of acid. Organic acids produce long gel and ceramic fibers, due to the beneficial effect of the long polymeric chains that are generated in the precursor gel. However the longest, strongest, densest and with the highest homogeneity fibers are obtained when acrylic acid is used. The linear shape of the molecular structure of acrylic acid, together with a lower content of organic species to be released, is favourable to the preparation of round and crack free PZT fibers, when acrylic acid is used.     

Excimer Laser Surface Treatment of Sheet Molding Compound for Adhesive Bonding

High-strength adhesive bonding of polymer composites can be achieved by treating surface with an excimer laser. A sheet molding compound (SMC) was used for the laser surface treatment for adhesive bonding. By subjecting the SMC surface to excimer laser source, the epoxy matrix was selectively removed by ablation, where upon the glass fibers stood exposed, without any inherent damage to their surface. The controllability is proved to be admirable by optimizing processing parameters. A significant improvement of the joint strength was found in the excimer laser treatment. The selective ablation of polymer matrix resulted in a maximized surface roughness, and an interlocking effect: of glass fibers at the joints. It is also possible that capillary effect draws the adhesive between the mating surfaces. This investigation shows that a high quality adhesive joint of polymer composites can be obtained from the excimer laser treatment.     

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.     

Fiber-optic transmission of stretched pulses from a Q-switched ruby laser

Fiber-optic transmission of Q-switched ruby laser pulses is limited by fiber damage owing to the high laser-beam intensities. Pulse stretching with a semiconductor-based control circuit for the Pockels cell of the ruby laser to reduce the peak intensities is described. Pulses with durations from 200 ns to 1 μs and a coherence length of ~3 m were generated. These pulses were coupled into multimode optical fibers to investigate the transmission characteristics and the limits of transmittable pulse energies. Stretched pulses can be transmitted in quartz fibers with a 600-μm core diameter to pulse energies of 300 mJ, which is an increase by a factor of 4 compared with standard Q-switched pulses. It is expected that beam guiding of ruby laser pulses by fiber optics will significantly facilitate the use of holographic interferometry in technical applications such as vibration analysis.     

Fundamental imaging properties of transillumination laser CT using optical fiber applicable to bio-medical sensing

We proposed and developed a novel transillumination laser CT imaging system, using optical fibers, based on the optical heterodyne detection method for biomedical use. The use of optical fibers enables portability and robustness against environmental changes such as varying temperature, air-flow shifts, and unexpected vibrations. In addition, motion-artifact-free images can be obtained with the present system as measurements can be performed with the object fixed. We experimentally investigate in detail the fundamental imaging properties of the system, that has a spatial resolution of 500 /spl mu/m, a dynamic range of approximately 110 dB, and a minimum-detectable-optical power of 10/sup -14/ W as a result of the excellent properties of the heterodyne detection. Based on experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the transillumination mode, similar to X-ray CT, at sub-millimeter spatial resolution and can derive quantitative information from the images. Finally, we experimentally demonstrate the first in-situ tomographic images of plants using the fiber-optic-based laser CT system.     

Bundled hollow optical fibers for transmission of high-peak-power Q-switched Nd:YAG laser pulses

A hollow-fiber bundle was designed and used to deliver high-peak-power pulses from a Q-switched Nd:YAG laser. An 80 cm long bundle with a total diameter of 5.5 mm was composed of 37 glass capillaries with bore diameters of 0.7 mm. Beam-resizing optics with two lenses were used to couple the laser beam into the bundle. The measured coupling loss due to the limited aperture ratio of the bundle was 2.3 dB, and the transmission loss at wavelengths of 1064 and 532 nm was 0.3 dB. When an inert gas flowed through the bores of the capillaries, the maximum output pulse energy was 200 mJ, which was the limit of the laser used in the experiment. Hollow-fiber bundles withstand irradiation better than single hollow fibers and silica-glass optical fibers do. They are suitable for many dermatological applications because they can be used to irradiate a large area.     

Conductive and Elastic 3D Helical Fibers for Use in Washable and Wearable Electronics

Due to the intrinsic properties of fabrics, fabric-based wearable systems have certain advantages over elastomeric material-based stretchable electronics. Here, a method to produce highly stretchable, conductive, washable, and solderable fibers that consist of elastic polyurethane (PU) fibers and conductive Cu fibers, which are used as interconnects for wearable electronics, is reported. The 3D helical shape results from stress relaxation of the prestretched PU fiber and the plasticity of the Cu fiber, which provides a predictable way to manipulate the morphology of the 3D fibers. The present fibers have superior mechanical and electrical properties to many other conductive fibers fabricated through different approaches. The 3D helical fibers can be readily integrated with fabrics and other functional components to build fabric-based wearable systems.     

Multi-walled carbon nanotubes and poly(lactic acid) nanocomposite fibrous membranes prepared by solution blow spinning

Nanocomposite fibers based on multi-walled carbon nanotubes (MWCNT) and poly(lactic acid) (PLA) were prepared by solution blow spinning (SBS). Fiber morphology was characterized by scanning electron microscopy (SEM) and optical microscopy (OM). Electrical, thermal, surface and crystalline properties of the spun fibers were evaluated, respectively, by conductivity measurements (4-point probe), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), contact angle and X-ray diffraction (XRD). OM analysis of the spun mats showed a poor dispersion of MWCNT in the matrix, however dispersion in solution was increased during spinning where droplets of PLA in solution loaded with MWCNT were pulled by the pressure drop at the nozzle, producing PLA fibers filled with MWCNT. Good electrical conductivity and hydrophobicity can be achieved at low carbon nanotube contents. When only 1 wt% MWCNT was added to low-crystalline PLA, surface conductivity of the composites increased from 5 x 10(-8) to 0.46 S/cm. Addition of MWCNT can slightly influence the degree of crystallinity of PLA fibers as studied by XRD and DSC. Thermogravimetric analyses showed that MWCNT loading can decrease the onset degradation temperature of the composites which was attributed to the catalytic effect of metallic residues in MWCNT. Moreover, it was demonstrated that hydrophilicity slightly increased with an increase in MWCNT content. These results show that solution blow spinning can also be used to produce nanocomposite fibers with many potential applications such as in sensors and biosensors.     

Measurement of launching efficiency into multimode optical fibersusing semiconductor laser diodes

A detailed and systematic study has been carried out of the launching efficiency of light, from semiconductor laser diodes into graded-index multimode optical fiber waveguides. Four different terminations of the fibers were investigated: plane-ends, hemispherical ends, taper-with-hemisphere ends, and roof-top (RT) ends. Besides launching efficiency, the parameters of interest were the various misalignments, such as axial, lateral, and angular, between laser and fiber, and the effect of these to produce a reduction in the launching efficiency. It is shown that RT fibers increase the launching efficiency considerably but rotational optimization of the fiber about its axis is essential. It is noted that this is a considerable disadvantage as most of the other techniques considered do not require the optimization     

光纤光栅环形镜的全光纤调Q 掺铒光纤激光器

报道一种新型全光纤调Q掺铒光纤激光器,在其结构中采用带有光纤光栅的光纤环形镜作 为调Q装置。此调Q方案同时提供了腔内损耗调制和对激光输出波长选择的功能。与声光、电光等调Q相比,其输出脉冲比较宽。但此全光纤Q开关装置与光纤熔接损耗小,从而克服了体光学调制器与光纤对接时插入损耗高的特点。     

Single-Crystal Laser-Heated Pedestal-Growth Sapphire Fibers for Er:YAG Laser Power Delivery

The Er:YAG laser-induced damage (LID) threshold and modal properties of single-crystal sapphire fibers grown by the laser-heated pedestal-growth method have been measured. The lowest loss (~0.4-dB/m) sapphire fibers produce little mode mixing and therefore deliver a near-single-mode output profile if the Er:YAG laser input beam profile is also nearly Gaussian. Normally, however, Er:YAG laser output beam profiles are multimode with numerous high-energy spikes. This leads not only to a multimode output from the fiber but also increased fiber loss that is due to higher-order mode coupling. The results of LID testing give a damage fluence of ~1.4 kJ/cm(2) for 300-mum core-only sapphire fibers at 2.94 mum.     

LASERIX: An open facility for developments of EUV and soft X-ray lasers and applications—Developments of XUV sources using high power laser facilities: ILE, ELI

LASERIX is a high-power laser facility leading to High-repetition-rate XUV laser pumped by Titanium:Sapphire laser. The aim of this laser facility is to offer Soft XRLs in the 30-7 nm range and auxiliary IR beam, which could also be used to produce synchronized XUV sources. In this contribution, the main results concerning both the development of XUV sources and their use for applications (irradiation of DNA samples) are presented, as well the present status and some perspectives for LASERIX.     

Layer-by-layer nanocoating of lignocellulose fibers for enhanced paper properties

The systematic modification of the surface charge of lignocellulose fibers was performed with a polyelectrolyte layer-by-layer (LbL) nanocoating process to produce negatively and positively charged fibers. The fibers were coated with 20-50 nm thick polymer surface layers which subsequently increased interaction between the fibers during paper formation. The modified fibers were added to standard fibers at varying proportions to produce paper with corresponding variation in properties such as strength and electrical conductivity. Paper strength was doubled by manipulating the surface charge and coating thickness of the LbL-treated pulp fibers. It is demonstrated that the LbL coating process increased the fiber interactions and that these interactions enhanced the paper properties. This process, when applied to a simulated sample of recycle grade of fibers, produce paper with an increase in tear strength as compared with untreated fiber paper. Nanocoating fibers with polythiophene/polyallylamine multilayers produced marginally conductive pulp and paper. Paper electrical conductivity was proportional to the number of the bilayers deposited.