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At least 1,729 records · Page 96Linked to original sources
PubMed2003

Electrical and optical properties of semiconductor nanocrystals.

Application of semiconductor nanocrystals in optoelectronic devices requires an understanding not only of their emission and absorption properties, but also of the processes of charge injection and transport in nanocrystalline films. Here, we present measurements of the electrical properties of nanocrystalline films and of blends of nanocrystals with conjugated polymers. We also describe the attachment of nanocrystals to semiconductor surfaces, and we investigate the emission of nanocrystalline films in microcavity structures and at high excitation intensities.

Journal Article↗
PubMed2005

Photonic devices based on preferential etching.

We introduce a design concept of optical waveguides characterized by a practical and reproducible process based on preferential etching of crystalline silicon substrates. Low-loss waveguides, spot-size converters, and power dividers have been obtained with polymers. We have also aligned liquid crystals in the waveguides and demonstrated guided propagation. Therefore this technology is a suitable platform for soft-matter photonics and heterogeneous integration.

Journal Article↗
PubMed2001

Eye movements and reading with large print and optical magnifiers in macular disease.

PURPOSE: Reading rate has been the main performance measure in studies that have compared reading with large print and optical magnifiers; eye movement characteristics have not been considered. We compared both eye movement characteristics and reading rates for subjects with macular disease reading without and with a range of low-vision devices. METHODS: Silent reading rate and eye movement characteristics for text passages at critical print size of 21 subjects aged 14 to 88 years with macular disease were measured with and without their preferred low-vision device. Saccadic frequency was determined from a sequencing task comprising five letters each separated by 5 degrees. Eye movements were recorded using an infrared limbal reflection system. RESULTS: There were no significant differences in reading rate, fixation durations, saccade numbers per word, or percent retrace time when using a low-vision device compared with reading without a low-vision device. The percentage of regressions was, however, lower with the low-vision device. Saccadic frequency in the sequencing task was predictive of reading performance with and without a low-vision device. CONCLUSIONS: When reading at critical print size, in terms of reading rate or saccades per word, there was no advantage to using large print over an optical low-vision device.

Adolescent↗
PubMed2003

Optical biosensor analysis in studying herpes simplex virus glycoprotein D binding to target nectin1 receptor.

Studies on molecular interactions between cellular receptors of herpes simplex virus (HSV) and the viral glycoproteins showing receptor-binding activity are of great relevance for understanding the molecular basis of virus entry. Information on such interactions further provides the basis for a rational design of antiviral drugs. A variety of biochemical and biophysical methodologies are used for determining the binding parameters of interacting biomolecules. Most of them require relatively high amounts of the analyzed compounds, or the use of labeled target molecules. Here, we report the study of the binding of two recombinant forms of HSV glycoprotein D, gD(Delta 290-299t) and gD(305t), and a recombinant form of the human cellular receptor for HSV, nectin1-Fc, by using an optical biosensor (IAsys Plus, Affinity Sensors, UK). This device detects and quantifies the changes in refractive index in the vicinity of the surface of sensor chips to which ligands are immobilized. The changes in the refractive index are proportional to the change in the absorbed mass, thus the analysis allows the monitoring of the interaction process in real-time and the determination of the binding parameters. HSV cellular receptor has been immobilized on the surface of the biosensor cuvette, bearing a carboxymethyl dextran layer. The immobilized receptor cuvette was then used for the binding experiments of the two glycoproteins. A significant difference in their dissociation constants was determined, showing for the gD(Delta 290-299t) protein a much higher affinity (K(D), 2.8 x 10(-7) M) with respect to gD(305t) (K(D), 2.8 x 10(-6) M). The active ligand concentration decreased on time, however the binding properties of the immobilized receptor were maintained over 5 weeks.

Animals↗
PubMed2004

Optical characteristics of a refractive optical attenuator with respect to the wedge angles of a silicon optical leaker.

We design, fabricate, and characterize the micromachined refractive variable optical attenuator (VOA) with a wedge-shaped silicon optical leaker (SOL). The vertical structures of the VOA device can be simply fabricated by deep reactive ion etching with no sidewall metallization, and the 8 degrees angled fibers are employed for a high return loss even in air-ambient conditions. The SOL successively transmits and refracts part of the incident light far outside the acceptance angle of the output fiber, showing an effective optical attenuation. The fabricated VOA gives high optical performances, such as a response time of 6 ms, a return loss of 39 dB, an insertion loss of 0.6 dB, an attenuation range of 43 dB, and a polarization-dependent loss (PDL) of a 10% attenuation level, including a wavelength-dependent loss. The optical characteristics of the VOA are also theoretically investigated with respect to the wedge angles of the SOL. The experimental characteristics are in good agreement with the theoretical values calculated, considering light scattered from the endface of an optical fiber and sidewall of the SOL. The PDL estimation was confirmed especially to sufficiently explain the fundamental characteristic of the PDL for the refractive VOA.

Journal Article↗
PubMed1994

Hippocampal reflected optical patterns during sleep and waking states in the freely behaving cat.

We examined reflected light as a measure of neural activity from a 2 mm2 area of dorsal hippocampus and surrounding neocortex in nine freely behaving cats during sleep and waking states. Light reflectance at 660 or 700 nm was measured by a coherent fiber optic probe attached to a charge-coupled device video camera that allowed acquisition of images from subcortical structures. In the dorsal hippocampus, rapid eye movement sleep (REMS) and active waking (AW) resulted in a significant decline (-0.9% +/- 0.3 and -2.0% +/- 0.5, respectively) in overall reflected light from the dorsal hippocampus relative to quiet sleep (QS), while quiet waking (QW) resulted in an overall increase (+2.0% +/- 0.4). In the neocortical probe placement group, reflectance also decreased during AW (-1.6% +/- 0.5) and increased during QW (+1.7 +/- 0.6) as compared to QS. In contrast to the hippocampus, however, overall reflectance increased, rather than decreased, in the neocortex during REMS (+2.7% +/- 1.3). We interpret a decline in reflectance as representing increased activation of underlying neural tissue. Thus, the cat dorsal hippocampus increased overall activity during REMS as compared to QS, while neocortical structures decreased overall activity during the same state. These results concur with expected activity changes based on electrophysiologic and autoradiographic studies. The imaging procedure provided a continuous assessment of spatially organized neural activity changes in the freely behaving animal.

Animals↗
PubMed2001

Radiation dosimetry using three-dimensional optical random access memories.

Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that ionizing radiation in the form of heavy charged particles is capable of changing the information originally stored on the ORAM material. The magnitude and spatial distribution of these changes are used as a measure of the absorbed dose, particle type and energy. The effects of exposure on 3D ORAM materials have been investigated for a variety of particle types and energies, including protons, alpha particles and 12C ions. The exposed materials are observed to fluoresce when exposed to laser light. The intensity and the depth of the fluorescence is dependent on the type and energy of the particle to which the materials were exposed. It is shown that these effects can be modeled using Monte Carlo calculations. The model provides a better understanding of the properties of these materials. which should prove useful for developing systems for charged particle and neutron dosimetry/detector applications.

Alpha Particles↗
PubMedDate not supplied

Laser-based capillary polarimeter.

A laser-based capillary polarimeter has been configured to allow for the detection of optically active molecules in capillary tubes with a characteristic inner diameter of 250 microm and a 39-nL (10(-9)) sample volume. The simple optical configuration consists of a HeNe laser, polarizing optic, fused-silica capillary, and charge-coupled device (CCD) camera in communication with a laser beam analyzer. The capillary scale polarimeter is based on the interaction between a polarized laser beam and a capillary tube, which results in a 360 degree fan of scattered light. This array of scattered light contains a set of interference fringe, which respond in a reproducible manner to changes in solute optical activity. The polarimetric utility of the instrument will be demonstrated by the analysis of two optically active solutes, R-mandelic acid and D-glucose, in addition to the nonoptically active control, glycerol. The polarimetric response of the system is quantifiable with detection limits facilitating 1.7 x 10(-3) M or 68 x 10(-12) nmol (7 psi 10(-9) g) sensitivity.

Calibration↗
PubMed1995

Fiber-optic DNA sensor for fluorometric nucleic acid determination.

Single-stranded deoxyribonucleic acid (ssDNA) thymidylic acid icosanucleotides (dT20) were synthesized on the surfaces of derivatized quartz optical fibers to create an optical DNA biosensor. The synthesis made use of an automated solid-phase synthesizer and phosphoramidite synthons. The covalently immobilized oligomers were found to hybridize with complementary ssDNA (cDNA) or ssRNA (cRNA) from solution, and the device was regenerable for multiple cycles of application. Hybridization on optical fibers was detected by the use of the fluorescent DNA stain ethidium bromide (EB). The procedure used hybridization assay techniques and provided a detection limit of 86 ng x mL(-1) cDNA and a sensitivity of 200% fluorescence intensity increase per 100 ng x mL(-1) of cDNA, with one cycle of hybridization analysis requiring 45 min. The sensor has been observed to be regenerable (minimum of five cycles) and to sustain full activity after prolonged storage times (1 year), harsh washing conditions (sonication), and sterilization (autoclaving). The extent of hybridization between the immobilized and complementary nucleic acid strands was determined by UV absorbance thermal denaturation studies wherein all 20 bases on each strand of the nucleic acid were found to be involved in duplex formation.

Biosensing Techniques↗
PubMed2004

Poly(dimethylsiloxane) hollow Abbe prism with microlenses for detection based on absorption and refractive index shift.

In this paper we report on an optical detection method that utilizes two physical effects for signal transduction, namely absorption and shift of refractive index. The device consists of a hollow prism and was fabricated by means of soft-lithography. It exhibits a high degree of monolithic integration. In order to keep down the amount of external equipment that is necessary to run the device, we were able to integrate several functions, such as focussing of light and alignment of optical fibres. Since all components are fabricated in the same material and in the same process, compatibility with other microfluidic devices or components can be achieved easily. The functional efficiency and the performance of the detector were tested by investigating solutions containing fluorescein, with concentrations between 5 and 1000 microM. The results clearly show the two regions in which the two physical effects are effective.

Journal Article↗
PubMed2006

Parametric oscillation in vertical triple microcavities.

Optical parametric oscillation is a nonlinear process that enables coherent generation of 'signal' and 'idler' waves, shifted in frequency from the pump wave. Efficient parametric conversion is the paradigm for the generation of twin or entangled photons for quantum optics applications such as quantum cryptography, or for the generation of new frequencies in spectral domains not accessible by existing devices. Rapid development in the field of quantum information requires monolithic, alignment-free sources that enable efficient coupling into optical fibres and possibly electrical injection. During the past decade, much effort has been devoted to the development of integrated devices for quantum information and to the realization of all-semiconductor parametric oscillators. Nevertheless, at present optical parametric oscillators typically rely on nonlinear crystals placed into complex external cavities, and pumped by powerful external lasers. Long interaction lengths are typically required and the phase mismatch between the parametric waves propagating at different velocities results in poor parametric conversion efficiencies. Here we report the demonstration of parametric oscillation in a monolithic semiconductor triple microcavity with signal, pump and idler waves propagating along the vertical direction of the nanostructure. Alternatively, signal and idler beams can also be collected at finite angles, allowing the generation of entangled photon pairs. The pump threshold intensity is low enough to envisage the realization of an all-semiconductor electrically pumped micro-parametric oscillator.

Journal Article↗
PubMed2004

Catheter-based in vivo imaging of enzyme activity and gene expression: feasibility study in mice.

PURPOSE: To construct and evaluate an interventional catheter-based imaging system for intravital monitoring of molecularly sensitive near-infrared fluorescent probes and optical marker genes. MATERIALS AND METHODS: An imaging device that was based on a miniaturized fiberoptic sensor (MIFS) was built in which images created with a 2.7-F fiberoptic catheter were relayed through a dichroic mirror, through a bandpass filter, and on two independent cameras. This system permitted simultaneous recording of white-light and fluorescent images. Spatial resolution, spectral transmissions, and sensitivity were determined in vitro. In vivo testing was performed in nude mice bearing intraperitoneal tumors that express green fluorescent protein and in a mouse model of ovarian carcinoma with enzyme-activatable near-infrared probes sensitive to tumoral protease activity. Signal intensity on images of tumors and that on images of normal tissue were measured and compared with t test. RESULTS: The catheter, which was advanced through an 18-gauge sheath, showed resolution of 7 line pairs per millimeter and detection limit for fluorochrome Cy5.5 of 1-10 pmol. Detection of endogenous green fluorescent protein gene expression was feasible in tumor nodules smaller than 1 mm in diameter (mean tumor signal intensity, 153.26 +/- 26.45 [SD], compared with that of adjacent nontumoral tissue of 36.73 +/- 11.69; P <.008). Similarly, activation of the near-infrared probe by tumoral proteases could be detected in peritoneal tumor seeds of ovarian cancer model with mean tumor signal intensity of 246.33 +/- 7.77 compared with that of adjacent nontumoral tissue of 41.56 +/- 18.64 (P <.001). Mean contrast-to-noise ratio in the near-infrared channel exceeded white-light contrast-to-noise ratio by a factor of 6.7 (P <.02). CONCLUSION: With this system, in vivo MIFS imaging of gene expression, enzyme activity, and potentially other molecular events is feasible, through direct interventional access to several organs and body cavities and potentially through transvascular approaches.

Animals↗
PubMed1997

[2nd generation bio-integrated keratoprosthesis. Implantation in animals].

PURPOSE: Our goal was to evaluate a second generation biointegrable keratoprosthetic device (BioKpro II). METHODS: The device consists of a porous transparent PTFE (12 mm diameter) and a soft copolymer structure for the optical system (7 mm diameter). Intraocular pression was evaluated with a Goldmann tonometer on an artificial chamber. A lamellar dissection was carried out 3 mm radially for 360 degrees creating a pocket to accommodate the skirt. The soft optic (42.5 D; 500 microns thick) was positioned through a hole (6 mm in diameter) trephined in the central cornea. A 360 degrees peritomy was performed and conjunctiva was placed in front of the prosthesis, sutured and was opened 15 days post implantation. 14 rabbits were implanted and were allowed to heal for three months. RESULTS: We are able to measure the intraocular pressure by Goldmann tonometer on an artificial chamber. We did not observed epithelialisation on the hydrophilic optical surface (14/14). Aseptic necrosis in direct contact between cornea and the soft optical system was observed when conjunctiva was not effective (4/14). As observed with the first generation devices, conjunctiva or buccal mucosa is needed to avoid local necrosis. In other cases no adverse reactions were observed after implantation. DISCUSSION: The geometry and biomechanical properties of the BioKpro II is closed to that of the human cornea. The junction between the optical and the flange was bound by polymeric interpenetration and prosthesis dislocation was not seen under pressure over 1000 mmHg. CONCLUSION: Second generation biointegrable keratoprostheses (BioKpro II) can be implanted successfully. Further tests will determine if surface modifications designed to promote epithelial cell attachment on the optical system could prevent ulceration at the junction between the fluorocarbon and the core.

Animals↗
PubMed1996

Applications of the optical trapping technique to analyze chemical reactions in single emulsion particles.

The applicability of the single beam gradient force optical trap and the optical levitation technique to investigate dynamic processes in microparticles is examined. The device allows to follow chemical reactions, like the emulsion polymerization and the ester hydrolysis reaction, in single emulsion droplets. Furthermore the usability of optical traps to investigate living cells is demonstrated.

Journal Article↗
PubMed1995

Automatic exposure control in retinal laser therapy.

Retinal laser spots are often over- or underexposed due to inhomogeneities of fundus pigmentation or variations in the radiation power impinging on the retina. We developed a method to control the exposure time of each individual spot of retinal laser photocoagulation in real time. The laser light reflected from the spot area is recorded by a detector. The intensity of this light increases during the exposure due to bleaching of the retinal pigment. If the reflected light reaches a predefined level, the laser apparatus is immediately stopped by a computer, which controls the whole process. The procedure was tested in enucleated porcine eyes. After verification of the proper function, a pilot study in a small collective of 19 patients (20 eyes, 25 sessions) with clear optical media was performed. In all cases, the apparatus worked safely. Visible indications for overexposed spots, particularly bleeding in extreme cases, did not occur. However, about 2%-5% of the spots were underexposed, mainly due to eye movements of the patient during the coagulation. Large variations in the automatically controlled exposure time confirm the difficulty in properly adjusting this parameter without such an automatic device. However, to be applicable to patients with opaque optical media, the method must be improved.

Adult↗
PubMed1983

Basics of videodisc and optical disk technology.

This article outlines basic videodisc and optical disk technology. Both optical and capacitance videodisc technology are described. Optical disk technology as a mass digital image and data storage device is defined and briefly compared with other established information storage media including magnetic tape and microforms. The article includes a look into the future of videodisc and optical disk.

Information Systems↗
PubMed1992

Digital archive center: implementation for a radiology department.

OBJECTIVE: In this article, we describe the implementation of a digital archive center for a radiology department in a 700-bed teaching hospital. MATERIALS AND METHODS: The archive center consists of two identical archive systems, each comprising five components: an archive server, a data-base server, an optical disk library, a stand-alone optical disk drive, and a communication network. An image management system controls the image traffic from acquisition devices to display stations. A fault-tolerant mechanism was built into the archive center to achieve a 100% uptime. RESULTS: The center has been in operation for over 6 months. We have not experienced a single total system failure during this period. It currently archives all digital images from three MR units and four CT scanners and selected images from three computed radiographic systems and two laser film digitizers. The center archives between 1.5 and 2.0 gigabytes of images per workday. CONCLUSION: With its built-in fault-tolerant mechanism, we believe that the implemented archive center is very reliable and is suitable for a radiology department to archive its digital images.

Hospital Bed Capacity, 500 and over↗