In situ study on the curing process of calcium phosphate bone cement

The aim of this study was to follow the entire curing process of modified alpha-TCP cement, and to explore how the liquid phase affects the curing reaction. Two calcium phosphate bone cements (CPCs) with a variety of aqueous solution were studied for comparison. In situ X-ray diffraction analysis and pH testing were employed to follow the chemical reaction, while quantitative ultrasonic measurement (QUS) was carried out to monitor the physical change. Results showed that CPC powders were completely consumed after 72 h. Two steps were presented in apatite formation. The first step was the precipitation of carbonated hydroxyapatite (CHA), and in the second step, conversion of calcium deficient hydroxyapatite (CDHA) was the dominant reaction. Finally, CPCs were fully converted to apatite except the cement with NaH2PO4 as liquid phase, because acidic environment inhibited the conversion of apatite. The pH increased linearly after mixing, when supersaturation was reached, it decreased to pH approximately 6.0 gradually. Ultrasound measurement indicated that the variation of speed of sound (SOS) was related to both apatite formation and microstructural evolution. Ultrasonic attenuation coefficient (UAC) was able to quantitatively describe the curing process from viscous paste to elastic solid as a function of curing time. Moreover, the curing reaction conformed to classical dissolution-precipitation mechanism.     

Apodizing holographic gratings for the modal control of semiconductor lasers

We first present the fabrication technique of apodizing holographic gratings. Gratings with a spatially variable reflectivity profile were obtained by the interference of two Gaussian beams on a glass plate covered with a photoresist. When the exposure time was short enough to avoid saturation of the photoresist, gratings with a quasi-Gaussian reflectivity profile for the beam reflected in the -1 order were produced; the reflectivity at the center could be as high as 71%, and the half-width of the reflectivity profile at the e(-1) position could be as small as 180 mum. Apodizing gratings were used as the end mirror of the external cavity of a broad-area semiconductor laser. Single longitudinal- and lateral-mode operation was observed over the full range of allowed injection currents.     

Design of cascaded volume holographic gratings to increase the number of channels for an optical demultiplexer

The design and demonstration of a holographic optical demultiplexer based on cascaded volume holographic gratings are presented. By serially adding a second holographic grating, which has a different grating period, slant angle, and center wavelength compared with those of the first grating, the operating wavelength range of the optical demultiplexer could be expanded, and, therefore, the number of channels of the holographic demultiplexer is doubled. As a result of the experiment, a 0.4 nm spaced 130- channel demultiplexer with a channel uniformity of 3.5 dB, a 3 dB bandwidth of 0.12 nm, and channel cross talk of -20 dB is experimentally achieved.     

Diffraction characteristics with various polarizations of overlapping holographic gratings in a uniaxial crystal

By the Riemann method, a coupled wave model is derived for the ordinary-to-ordinary (OO) and extraordinary-to-extraordinary (EE) Bragg diffraction of a Gaussian beam by overlapping holographic gratings in a uniaxial crystal. The computer simulation is used to discuss the relations among the diffraction efficiency, the index modulation, the wavelength sensitivity, the angular sensitivity, and the the widths of the recording and reading beams. The characteristics of EE and OO diffraction in a uniaxial crystal are found to be remarkably different. The simulation shows that EE diffraction may exhibit far higher diffraction efficiency than does OO diffraction for very low index modulation with the same hologram size, for example, nearly 90% when the size is 8.2 x 10(-5).     

In situ measurements of optical parameters in Lake Baikal with the help of a Neutrino telescope

We present results of an experiment performed in Lake Baikal at a depth of approximately 1 km. The photomultipliers of an underwater neutrino telescope under construction at this site were illuminated by a distant laser. The experiment not only provided a useful cross-check of the time calibration of the detector but also allowed us to determine inherent optical parameters of the water in a way that was complementary to standard methods. In 1997 we measured an absorption length of 22 m and an asymptotic attenuation length of 18 m. The effective scattering length was measured as 480 m. By use of (cos theta) = 0.95 (0.90) for the average scattering angle, this length corresponds to a geometric scattering length of 24 (48) m.     

In situ optical characterization and reengineering of interference coatings

A new optical monitoring system has been developed that allows recording of transmission spectra in the wavelength range between 400 and 920 nm of a growing optical coating during deposition. Several kinds of thin film sample have been prepared by use of a hybrid monitoring strategy that is essentially based on a combination of quartz monitoring and in situ transmission spectra measurements. We demonstrate and discuss the applicability of our system for reengineering procedures of high-low stacks and measurements of small vacuum or thermal shifts of optical coatings.     

A study of the effect of a corona discharge on recording of holographic diffraction gratings in the Cu-As2S3 structure

Improvement of the optical recording process in the Cu-As₂S₃ structure in the whole visible band was observed when the structure is simultaneously exposed and charged in the field of a negative corona discharge as compared to the standard direct recording in the above-mentioned structure. It was shown that using the negative corona discharge for recording in these structures allows the holographic sensitivity and diffraction efficiency of the recorded holographic diffraction gratings to be increased several-fold compared to gratings obtained by the standard approach. The results are discussed using the known photoelectrical model.     

Fabrication of a multichannel wavelength-division multiplexing-passive optical net demultiplexer with arrayed-waveguide gratings and diffractive optical elements

A novel, to our knowledge, integrated wavelength-division multiplexing-passive optical net demultiplexer that uses an arrayed-waveguide grating and diffractive optical elements is presented. The demultiplexer is used to distribute 1.3-mum wavelength signals and to multiplex an eight-channel wavelength-division multiplexer spectrum at a 1.55-mum wavelength. The device shows high functionality and good optical performance. The measured cross talk was less than -21 dB, and the 3-dB bandwidth was determined to be 97 GHz, which is close to the theoretical value of 93 GHz. Average losses of 4.5 and 8 dB were measured for the 1.3- and the 1.55-mum signals, respectively.     

In situ synthesis of porous ceramics with a framework structure of aluminium borate whisker

New porous ceramics with a framework structure of aluminium borate (9Al2O3 · 2B2O3) whiskers, in which the whiskers are distributed uniformly and randomly, can be synthesized in situ by firing of a green powder compact of a mixture of aluminium hydroxide, boric acid and an additive of nickel oxide above 1100°C. During firing, the whiskers of aluminium borate grow in situ in the compact, and are bonded together by sintering. The porous aluminium borate consists solely of whiskers, has a porosity of 85%–50%, which corresponds to a volume fraction of whiskers of 15%–50%, and a flexural strength of 2.2–56.1 MPa. Because the whiskers are strongly bonded to other whisker(s), the problem of whiskers scattering, that can be an inhalation hazard, is solved. The aluminium alloy matrix composite using this porous aluminium borate as reinforcement was fabricated by the squeeze-casting method. The tensile strength of the composite material with a whisker volume fraction of 20% can be improved by up to about 90% compared with the unreinforced matrix alloy at 350°C. © 1998 Chapman & Hall     

In situ monitoring of friction surfaces and their sequence pattern analysis

Friction occurs between solid surfaces, and even sometimes on lubricated surfaces. To understand tribological subjects, it is important to know the changes that occur in friction surfaces. In this study, a laser strobe technique is applied to a friction surface observation. The recorded surface images were analysed using pattern-matching methods and their correlations are discussed. A test using pin-on-plate methods with carbon steels was performed using a reciprocating motion speed of 10 Hz for 4.9 N. A pulsed laser light (Nd:YAG SHG=532 nm, 5 ns per pulse) was irradiated onto the friction surface. It was induced using an optical microscope that was located just to the side of the pin. The laser pulse was synchronized with the plate motion, which was a trigger of the laser pulse. The surface image was stored for every cycle. These sequences were calculated and their correlations were analysed as a function of the surface pattern and the friction track size and shape. Analysis revealed that some groups were distinguishable as parameters of the damage size and shape.     

In situ microparticle analysis of marine phytoplankton cells with infrared laser-based optical tweezers

We describe the application of infrared optical tweezers to the in situ microparticle analysis of marine phytoplankton cells. A Nd:YAG laser (λ= 1064 nm) trap is used to confine and manipulate single Nannochloris and Synechococcus cells in an enriched seawater medium while spectral fluorescence and Lorenz-Mie backscatter signals are simultaneously acquired under a variety of excitation and trapping conditions. Variations in the measured fluorescence intensities of chlorophyll a (Chl a) and phycoerythrin pigments in phytoplankton cells are observed. These variations are related, in part, to basic intrasample variability, but they also indicate that increasing ultraviolet-exposure time and infrared trapping power may have short-term effects on cellular physiology that are related to Chl a photobleaching and laser-induced heating, respectively. The use of optical tweezers to study the factors that affect marine cell physiology and the processes of absorption, scattering, and attenuation by individual cells, organisms, and particulate matter that contribute to optical closure on a microscopic scale are also described.     

Preparation and optical properties of organic/inorganic nanocomposite materials by UV curing process

In this study, photo-polymerized poly(acrylic)/silica hybrid thin films were prepared from various acrylic monomers and monodispersed colloidal silica with the coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films varied from 0 to 50 wt.%. The experimental results show that the particle size of silica in hybrid films could be effectively controlled at 15–20 nm as the weight ratio of MSMA to colloidal silica is higher than 0.68 and 0.60 for the poly(methyl methacrylate)/silica (US) and poly(ethylene glycol dimethacrylate-trimethylolpropane trimethacrylate)/silica (UDT) hybrid materials, respectively. The polymerization conversion for US and UDT hybrid materials could reach to 100% and 94.5%, respectively. The comparison of surface roughness with the film thickness is less than 0.10%, indicating the excellent surface planarity of the prepared hybrid thin films. Besides, the prepared hybrid films from the crosslinked acrylic polymer moiety show much better film uniformity, thermal stability and mechanical properties than those obtained from poly(methyl methacrylate). The refractive index decreases with increasing the silica content in the hybrid films. Excellent optical transparency is obtained in the prepared hybrid films. These results show that the prepared hybrid thin films have potential applications as passive films for optical devices.     

Interferometric determination of the electron density in a high-pressure xenon lamp with a holographic optical element

A new setup for plasma diagnostics is presented that is based on real-time holographic interferometry. The hologram is used as a holographic optical element (HOE) that combines the properties of a hologram, of a lens, and of a grating simultaneously. The HOE is responsible for the formation of the interference pattern, and, in addition, acts as an imaging element and prevents most of the plasma radiation from reaching the interferogram detection system. The spectral and imaging properties of this HOE are calculated numerically, and this numeric procedure is tested experimentally. We applied the HOE-interferometry technique to the measurement of the electron density in a brightly radiating high-pressure xenon lamp. The principle of this experiment, two-wavelength interferometry, is described, and the results of the measurement are presented and discussed.     

In situ observing the hydration process of K-PSS geopolymeric cement with environment scanning electron microscopy

The hydration process of K-PSS geopolymeric cement was in situ quantitatively investigated by environment scanning electron microscope (ESEM) under 80% relative humidity. An energy dispersion X-ray analysis (EDXA) was also employed to determine the chemical composition of the hydration product. The ESEM micrographs showed that metakaolin particles pack loosely at 10 min after an initial mixing, resulting in an existence of many large voids. As the hydration proceeded, some gels were produced and gradually precipitated on the surfaces of these particles. At a later stage, these particles were covered by thick gel layers, and their interspaces among the metakaolin particles were also completely filled up. The corresponding EDXA results illustrated that the molar ratios of K/Al and Si/Al decreased with the development of hydration. The molar ratios of K/Al and Si/Al of the hydration products at an age of 13 h amounted to 1.06 and 2.14 respectively, which were very close to the theoretical values (K/Al = 1.0, Si/Al = 2.0) for K-PSS geopolymeric cement hardened paste. In addition, well-developed crystals could not be found at any ages, instead sponge-like amorphous gels have always been observed during the whole hydration process.     

Preparation of highly conductive adhesives by in situ generated and sintered silver nanoparticles during curing process

The lower resistivity (7.5 × 10⁻⁵ Ω cm) of nano-electrically conductive adhesives (nano-ECAs) with silver flakes and in situ formed and sintered silver nanoparticles was developed. At room temperature,the silver nanoparticles (Ag NPs) could not be generated in ECAs due to no reaction between silver nitrate and N,N-dimethyl-4-aminobenzaldehyde (DABA). However, during curing process, Ag NPs were immediately generated through reducing silver nitrate by DABA in absence of stabilizing agents. At the same time, the increased viscosity of epoxy due to the curing could prevent the agglomerates of Ag NPs. Morphology studies showed that most Ag NPs have been attached onto the surfaces of silver flakes due to the good affinity between them, resulting in more effectively interconnecting with silver flakes by the sintered Ag NPs. Thus, the lower bulk resistivity was obtained. On the other hand, DABA, containing a tertiary amine, can stabilize contact resistance of nano-ECAs by effectively preventing galvanic corrosion at the interface between nano-ECAs and Sn surfaces due to the fact that amines can strongly bond to a Sn surface.     

In situ curing of sliding SU-8 droplet over a microcontact printed pattern for tunable fabrication of a polydimethylsiloxane nanoslit

A tunable process for polydimethylsiloxane (PDMS) nanoslit fabrication is developed for nanofluidic applications. A microcontact printing (μCP) of a laterally spreading self-assembled hexadecanethiol (HDT) layer, combined with in situ curing of a sliding SU-8 droplet, enables precise and independent tuning of a nanoslit-mold width and height using a single μCP master mold. The SU-8 nanoslit-mold is replicated using a hard-soft composite PDMS to prevent channel collapse at low (<0.2) aspect ratio (height over width). The fluidic characteristics as well as dimensions of nanoslits fabricated with various conditions are analyzed using a fluorescein sample and AFM images. Finally, concentration polarization-based sample preconcentration is successfully demonstrated at the nanoslit boundary where an electric double-layer is overlapped.     

Temperature control of the ultra-short laser pulse compression in a one-dimensional photonic band gap structure with nematic liquid crystal as a defect layer

We investigate numerically the controllable chirped pulse compression in a one-dimensional photonic structure containing a nematic liquid crystal defect layer using the temperature dependent refractive index of the liquid crystal. We consider the structure under irradiation by near-infrared ultra-short laser pulses polarized parallel to the liquid crystal director at a normal angle of incidence. It is found that the dispersion behaviour and consequently the compression ability of the system can be changed in a controlled manner due to the variation in the defect temperature. When the temperature increased from 290 to 305 K, the transmitted pulse duration decreased from 75 to 42 fs in the middle of the structure, correspondingly. As a result, a novel low-loss tunable pulse compressor with a really compact size and high compression factor is achieved. The so-called transfer matrix method is utilized for numerical simulations of the band structure and reflection/transmission spectra of the structure under investigation.     

In situ measurements and analysis of imidization extent, thickness, and stress during the curing of polyimide films

The effects of scanning rate and pre-baking time on the imidization extent, thickness, and stress of polyimide films during the curing process were simultaneously analyzed using FTIR and the strip end deflection detector complemented with interferometer systems. Film thickness and stress increased, but imidization extent decreased with increasing scanning rates. Longer pre-baking times significantly reduced the initial film thickness and stress. Imidization extent, thickness, and stress behavior of polyimide films during the curing process were closely related one another.     

High capacity optical beam forming for phased arrays with fiber gratings and frequency conversion for beat noise control

A new wavelength division multiplexing grating-based beam-forming architecture for phased arrays that can achieve the minimum possible number of optical interconnects is presented. A reduction in interconnect hardware of 99.6% is obtained for a 512-beam array, which is, as far as we know, the lowest number of interconnects reported to date. Analysis of the ultimate beam capacity limit of the beam former shows that the beat noise interference limitation is the most important factor. We present a new hybrid frequency-converting optical beam former that removes the fundamental beat noise limitation. This frequency downconverts the rf signal to an intermediate frequency before performing the true-time-delay equalization in the optical domain. The resulting advantage of reduced optical bandwidth per channel enables more wavelengths to be used for a given wavelength span, resulting in an increased beam capacity. A greater than sevenfold increase in beam capacity is demonstrated through the use of the frequency conversion technique, with 960 beams synthesized at 12.4 GHz, showing a 99.8% reduction in required interconnects.