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Results for “Optical Devices”

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At least 685 records · Page 38Linked to original sources
PubMed2000

Design and characterization of a laser-based instrument with spectroscopic feedback control for treatment of vascular lesions: the "Smart Scalpel".

To improve the effectiveness of microsurgical techniques, we are developing a semi-autonomous robotic surgical tool (called the "Smart Scalpel") as an alternate approach to treatment of vascular lesions. The device employs optical reflectance spectroscopy as part of a line scan imaging system to identify and selectively target blood vessels in a vascular lesion for thermal treatment with a focused laser beam. Our proof-of-concept reported here presents the design and construction of a prototype instrument, initial quantification of imaging system resolution and contrast, and preliminary verification of the imaging and targeting strategies with standard targets and live dermal tissue.

Animals↗
PubMed1997

Quantum-confined stark effect in single CdSe nanocrystallite quantum dots

The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state ( approximately 10(5) cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.

Journal Article↗
PubMed1999

Two-dimensional photonic band-Gap defect mode laser

A laser cavity formed from a single defect in a two-dimensional photonic crystal is demonstrated. The optical microcavity consists of a half wavelength-thick waveguide for vertical confinement and a two-dimensional photonic crystal mirror for lateral localization. A defect in the photonic crystal is introduced to trap photons inside a volume of 2.5 cubic half-wavelengths, approximately 0.03 cubic micrometers. The laser is fabricated in the indium gallium arsenic phosphide material system, and optical gain is provided by strained quantum wells designed for a peak emission wavelength of 1.55 micrometers at room temperature. Pulsed lasing action has been observed at a wavelength of 1.5 micrometers from optically pumped devices with a substrate temperature of 143 kelvin.

Journal Article↗
PubMed2002

The current diagnosis of superficial bladder cancer must be reconsidered.

The high recurrence and progression rates in superficial bladder cancer are partially related to the deficiencies of the standard conventional diagnostic modalities. Therefore, innovative noninvasive and invasive detection devices have been studied during the last decade. New diagnostic urine markers are under intensive investigation in order to exclude the presence of urothelial cancer, but the value of all these tests is still insufficiently validated in diagnosis and follow-up. With the introduction of 5-amino-levulinic acid fluorescence endoscopy, the efficacy of the detection device has been significantly improved. Flat lesions such as carcinoma in situ can be completely detected besides exophytic tumors. This is of particular importance because the fate of the patient depends to an important extent on these tumor entities. Furthermore, first experimental results using imaging devices like optical coherence tomography and confocal laser scanning microscopy promise new powerful noninvasive tools for 'optical sectioning' of the bladder.

Antigens, Neoplasm↗
PubMed2006

Nanocomposites based on conducting polymers and carbon nanotubes: from fancy materials to functional applications.

This review deals with recent progress on the development of nanocomposite materials formed by conducting organic polymers (COPs) and carbon nanotubes (CNs), both from a fundamental and applied point of view. The combination of the unique properties of CNs with COPs makes of these materials interesting multifunctional systems with great potential in many applications such as supercapacitors, sensors, photovoltaic cells and photodiodes, optical limiting devices, solar cells, high-resolution printable conductor, electromagnetic absorbers, and, last but not least, advanced transistors.

Carbon↗
PubMed2003

Toe pressure measurements compared to ankle artery pressure measurements.

The Trans-Atlantic Inter-Society Consensus (TASC)-recommended absolute toe pressure is < 30-50 mm Hg for definition of chronic critical limb ischemia (CLI). Toe pressures can be measured by different techniques. The authors analyzed the clinical use of the Doppler technique and an automatic device with optical sensors and estimated their value in documentation of chronic critical limb ischemia compared to ankle artery pressures. Three different investigations were performed: (1) In 16 healthy subjects the digital artery pressures were measured by using 3 different optical sensors (transmission, reflection, and microcirculation sensor) and compared to the systolic brachial pressure. (2) In 50 patients with and without peripheral arterial occlusive disease the toe pressures at digits 1 and 2 of both feet were determined by Doppler technique (8 MHz) and by optical sensors (cuff width constant 1.5 cm) and were compared to the ankle artery pressure determined by Doppler technique. (3) In 175 patients the toe pressures were measured at 1 toe and the ankle artery pressures were determined. In this group they estimated the clinical use of the toe pressure in regard to the definition of CLI (toe pressure < 50 mm Hg) compared to the ankle pressure < 70 mm Hg. The digital artery pressures measured with the different optical sensors, and the systolic brachial pressures were not significantly different and the correlation coefficients were around 0.7. In 21 of 50 patients the toe pressure at D1 and D2 could not be measured by Doppler technique because with the applied cuff no Doppler signal could be detected at the tip of the toe, but in 24 of these 29 patients the optical measurement was possible. Mean toe pressures at D1 were 108 +/- 45 mm Hg and D2 102 +/- 45 mm Hg, which were statistically not different. The correlation coefficient for the highest ankle artery pressure and the highest toe pressure determined by the Doppler technique was 0.389; for the highest ankle artery pressure and the toe pressure measured by the optical sensors it was 0.369, and for the toe pressures measured by Doppler technique and the optical sensors it was 0.506. Defining systolic ankle artery pressure < or = 50 to 70 mm Hg as the golden standard for CLI, the sensitivity of optical toe pressure measurement for the detection of CLI was 8%, the specificity was 96%, the positive predictive value 12%, and the negative predictive value was 94%. Independent of technique the absolute systolic toe pressures did not correlate with the absolute systolic ankle pressures. The optical measurement was more suitable for toe pressure measurement because it could be used in 90% of all patients. All in all, toe pressure measurements are more useful to exclude CLI than to prove it.

Adult↗
PubMed1999

Myosin II-independent F-actin flow contributes to cell locomotion in dictyostelium.

While the treadmilling and retrograde flow of F-actin are believed to be responsible for the protrusion of leading edges, little is known about the mechanism that brings the posterior cell body forward. To elucidate the mechanism for global cell locomotion, we examined the organizational changes of filamentous (F-) actin in live Dictyostelium discoideum. We labeled F-actin with a trace amount of fluorescent phalloidin and analyzed its dynamics in nearly two-dimensional cells by using a sensitive, high-resolution charge-coupled device. We optically resolved a cyclic mode of tightening and loosening of fibrous cortical F-actin and quantitated its flow by measuring temporal and spatial intensity changes. The rate of F-actin flow was evaluated with respect to migration velocity and morphometric changes. In migrating monopodial cells, the cortical F-actin encircling the posterior cell body gradually accumulated into the tail end at a speed of 0.35 microm/minute. We show qualitatively and quantitatively that the F-actin flow is closely associated with cell migration. Similarly, in dividing cells, the cortical F-actin accumulated into the cleavage furrow. Although five times slower than the wild type, the F-actin also flows rearward in migrating mhcA- cells demonstrating that myosin II ('conventional' myosin) is not absolutely required for the observed dynamics of F-actin. Yet consistent with the reported transportation of ConA-beads, the direction of observed F-actin flow in Dictyostelium is conceptually opposite from a barbed-end binding to the plasma membrane. This study suggests that the posterior end of the cell has a unique motif that tugs the cortical actin layer rearward by means of a mechanism independent from myosin II; this mechanism may be also involved in cleavage furrow formation.

Actins↗
PubMed1998

Diving speeds and angles of a gyrfalcon (Falco rusticolus)

An optical tracking device recorded the three-dimensional paths of 11 dives by a 1.02 kg gyrfalcon, trained to dive to a falconer. The dives started at altitudes up to 500 m above the ground and were inclined at angles of 17-62 degrees from the horizontal. The falcon controlled its speed during the dives, rather than simply falling from the sky, and the dives had three phases. During the first (acceleration) phase, the falcon accelerated to speed limits between 52 and 58 m s-1 in the seven fastest dives, evidently with minimum drag, because its accelerations were close to those predicted from theory for minimum drag. The falcon then began a constant-speed phase by increasing drag by a factor of 1.3-4.8 while still 100-350 m above the ground in most dives. The constant-speed phase lasted no more than a few seconds, and the falcon then began a deceleration phase by increasing its drag further, this time by factors of 1.7-3. 2, and decelerating with a mean value of -0.95 times gravitational acceleration. During all three phases, the dive angle was nearly constant or increased during the deceleration phase, and the falcon made no changes in its body shape that were obvious through the tracking device telescope except to reduce its wing span as it accelerated. The falconer, however, was close to the falcon at the end of the dive and could see that, during the deceleration phase, the falcon held its wings in a cupped position, apparently with a high angle of attack and therefore high drag. At the end of the deceleration phase, the falcon dropped its legs, spread its toes and finally spread its wings as it approached the falconer. Although the speeds reported here are the fastest ever measured with known accuracy in animals, the falcon could theoretically have reached more than 70 m s-1 if it had continued to accelerate with minimum drag until close to the ground. Even at this speed, it would have had enough altitude to pull out of the dive before crashing into the ground. Several authors have estimated that diving falcons reach speeds of more than 70 m s-1, and wild falcons may reach such speeds when they make long, steep dives upon birds flying high in the air.

Journal Article↗
PubMed2003

Particle concentrations in inner-city homes of children with asthma: the effect of smoking, cooking, and outdoor pollution.

Inner-city children have high rates of asthma. Exposures to particles, including allergens, may cause or exacerbate asthma symptoms. As part of an epidemiologic study of inner-city children with asthma, continuous (10-min average) measurements of particle concentrations were made for 2-week periods in 294 homes drawn from seven cities. Measurements were made using an optical scattering device that is most sensitive to fine particles. The concentrations recorded by these devices were corrected to agree with colocated outdoor gravimetric PM2.5 monitors. Indoor concentrations in the homes averaged 27.7 (standard deviation = 35.9) micro g/m3, compared with concurrent outdoor concentrations of 13.6 (7.5) micro g/m3. A multivariate model indicated that outdoor particles penetrated indoors with an efficiency of 0.48 and were therefore responsible for only 25% of the mean indoor concentration. The major indoor source was smoking, which elevated indoor concentrations by 37 micro g/m3 in the 101 homes with smokers. Other significant sources included frying, smoky cooking events, use of incense, and apartment housing, although the increases due to these events ranged only from 3 to 6 micro g/m3. The 10-min averaging time allowed calculation of an average diurnal variation, showing large increases in the evening due to smoking and smaller increases at meal times due to cooking. Most of the observed variance in indoor concentrations was day to day, with roughly similar contributions to the variance from visit to visit and home to home within a city and only a small contribution made by variance among cities. The small variation among cities and the similarity across cities of the observed indoor air particle distributions suggest that sources of indoor concentrations do not vary considerably from one city to the next, and thus that simple models can predict indoor air concentrations in cities having only outdoor measurements.

Air Pollutants↗
PubMed2002

Ideal concentrators with gaps.

Ideal concentrators with large gaps are presented. These new devices use optical elements surrounding the receiver. When their number is large, they (may) constitute a microstructure (many components with small sizes). Smaller gaps can also be achieved by use of a fewer number of optics. Different ways to combine these optical elements are presented for the case of larger and smaller gaps. Designs that use mirrors and total internal reflection are also presented for the case of larger gaps. The mathematical methods used to calculate the shape of the optics are outlined. In spite of the fact that the number of optics may be large, given the symmetries inherent to these designs, the elements in these microstructures are all equal. This is a simplifying feature that is important for their design and eventual production in the future.

Journal Article↗
PubMed2005

Simultaneous measurement of temperature and external refractive index by use of a hybrid grating in D fiber with enhanced sensitivity by HF etching.

We propose a dual-parameter optical sensor device achieved by UV inscription of a hybrid long-period grating-fiber Bragg grating structure in D fiber. The hybrid configuration permits the detection of the temperature from the latter's response and measurement of the external refractive index from the former's response. In addition, the host D fiber permits effective modification of the device's sensitivity by cladding etching. The grating sensor has been used to measure the concentrations of aqueous sugar solutions, demonstrating its potential capability to detect concentration changes as small as 0.01%.

Journal Article↗
PubMed2005

Optically reconfigurable azobenzene polymer-based fiber Bragg filter.

Optically writable, thermally erasable surface relief gratings in thin Disperse Red 1 polymethyl methacrylate azopolymer films were used to demonstrate an arbitrarily reconfigurable fiber Bragg filter. Gratings were optically written on azopolymer-coated side-polished fiber blocks, and a write-erase-write cycle was demonstrated. Finite difference time domain simulations reveal that this optically reconfigurable device concept can be optimized in a silicon-on-insulator waveguide platform.

Journal Article↗
PubMed2006

Optical cross-connect system based on the White cell and three-state microelectromechanical system: experimental demonstration of the quartic cell.

We present a proof of concept (design, simulations, and experimental results) for an optical cross-connection device based on the optical White cell and a three-state microelectromechanical system tilting mirror array. We describe in detail the implementation of an underpopulated quartic White cell configuration. We discuss the aberrations associated with the output of the system.

Journal Article↗
PubMed2006

Electrical-contact-free readout of the response of superconductive bolometer arrays using thermal cross talk.

We utilized and investigated the unique dependence of the magnitude and phase of the response on thermal cross talk between bolometer pixels in an array to measure the response of the devices through fewer monitoring devices. We show the feasibility of the proposed readout technique by use of two source pixels in an array, as the image-mapping devices, and one optically shielded pixel as the readout device. While the sensing pixels were electrical-contact free, the readout device was current biased in 4-probe current-bias configuration. Both the phase and the magnitude of the response due to the cross talk in the array were found to be strongly dependent on the modulation frequency and the distance between the sensing and the readout pixels. A series of measurements were designed to extract the response of each single-sensing pixel. By combining the measured data, the response of individual pixels could be extracted through the interpolation of the mapped responses.

Journal Article↗
PubMed2005

Ultrashort pulse propagation in uniform and nonuniform waveguide long-period gratings.

We conduct a detailed theoretical analysis of ultrashort pulse propagation through waveguide long-period grating (LPG) structures operating in the linear regime. We first consider the case of uniform LPGs, and we also investigate the effect of the typical grating nonuniformities, e.g., grating profile apodization, grating period chirping, and discrete phase shifts, on the spectral and temporal behavior of LPG structures. The two interacting modes are analyzed separately, and advanced representation tools, namely, space-wavelength and space-time diagrams (where space refers to the longitudinal grating dimension), are used to provide a deeper insight into the physics that determines the pulse evolution dynamics through the grating structures under analysis. In addition to its intrinsic physical interest, our study reveals the strong potential of LPG-based devices for optical pulse reshaping operations in the subpicosecond regime.

Journal Article↗