Biomedical subjects

Caesar Saloma

Publications and source records attributed to Caesar Saloma.

16 recordsLinked to original sources

PubMed2006

High-resolution mapping of quantum efficiency of silicon photodiode via optical-feedback laser microthermography.

We map the external quantum efficiency (QE) distribution of a silicon photodiode (PD) sample via a thermographic imaging technique based on optical-feedback laser confocal microscopy. An image pair consisting of the confocal reflectance image and the 2D photocurrent map is simultaneously acquired to delineate the following regions of interest on the sample: the substrate, the n-type region, the pn overlay, and the bonding pad. The 2D QE distribution is derived from the photocurrent map to quantify the optical performance of these sites. The thermal integrity of the sample is then evaluated by deriving the rate of change of QE with temperature T at each point on the silicon PD. These gradient maps function not only as stringent measures of local thermal QE activity but they also expose probable defect locations on the sample at high spatial resolution--a capability that is not feasible with existing bulk measurement techniques.

Journal Article↗

PubMed2005

In-line interferometer for direction-sensitive displacement measurements by optical feedback detection.

We demonstrate a compact in-line interferometer for direction-sensitive displacement measurement by optical feedback detection with a semiconductor laser (SL) light source. Two reflected beams from a semitransparent reference mirror and a reflecting test object interfere in the SL medium, causing a variation in its output power. The reference mirror is located between the SL output facet and the test object. The performance of the interferometer is investigated numerically and experimentally to determine its optimal operating conditions. We have verified the operating conditions where the behavior of the SL output power profile could indicate accurately the displacement magnitude and direction of the moving test object. The profile behavior is robust against variations in optical feedback and scale of the interferometer configuration.

Journal Article↗

PubMed2005

Rapid subsurface detection of nanoscale defects in live microprocessors by functional infrared emission spectral microscopy.

We demonstrate the rapid and nondestructive detection of subsurface nanometer-size defects in 90 nm technology live microprocessors with a new technique called functional infrared emission spectral microscopy. Broken, leaky, and good transistors with similar photoemission images are identified from each other by their different emission spectra that are calculated as linear combinations of weighted basis spectra. The basis spectra are derived from a spectral library by principal component analysis. Leaky transistors do not exhibit apparent morphological damage and are undetectable by optical or scanning probe microscopy alone. The emission signals from two or more transistors combined incoherently, and defect detection is primarily limited by the signal-to-noise ratio of the detected spectrum and not by the separation distance of neighboring transistors.

Journal Article↗

PubMed2005

Cluster formation by allelomimesis in real-world complex adaptive systems.

Animal and human clusters are complex adaptive systems and many organize in cluster sizes s that obey the frequency distribution D (s) proportional to s(-tau). The exponent tau describes the relative abundance of the cluster sizes in a given system. Data analyses reveal that real-world clusters exhibit a broad spectrum of tau values, 0.7 (tuna fish schools) <or=tau<or=4.61 (T4 bacteriophage gene family sizes). Allelomimesis is proposed as an underlying mechanism for adaptation that explains the observed broad tau spectrum. Allelomimesis is the tendency of an individual to imitate the actions of others and two cluster systems have different tau values when their component agents display unequal degrees of allelomimetic tendencies. Cluster formation by allelomimesis is shown to be of three general types: namely, blind copying, information-use copying, and noncopying. Allelomimetic adaptation also reveals that the most stable cluster size is formed by three strongly allelomimetic individuals. Our finding is consistent with available field data taken from killer whales and marmots.

Adaptation, Physiological↗

PubMed2004

High-contrast microscopy of semiconductor and metal sites in integrated circuits by detection of optical feedback.

High-contrast microscopy of semiconductor and metal sites in integrated circuits is demonstrated with laser-scanning confocal reflectance microscopy, one-photon (1P) optical-beam-induced current (OBIC) imaging, and detection of optical feedback by means of a commercially available semiconductor laser that also acts as an excitation source. The confocal microscope has a compact in-line arrangement with no external photodetector. Confocal and 1P OBIC images are obtained simultaneously from the same focused beam scanned across the sample plane. Image pairs are processed to generate exclusive high-contrast distributions of semiconductor, metal, and dielectric sites in a GaAs photodiode array sample.

Journal Article↗

PubMed2004

Pulsed full-color digital holography with a hydrogen Raman shifter.

We demonstrate pulsed full-color digital holography with a hydrogen Raman shifter as a single source of highly directional multiwavelength light. For the primary (blue, green, red) color channels we utilize the first three Stokes beam outputs (415.9, 502.9, and 635.9 nm) of the shifter (gas pressure, 1.38 MPa) that is pumped by the 355-nm output of a pulsed Nd:YAG laser (5.4-ns pulse width, 10-Hz repetition rate). We have developed a simple beam-conditioning system to improve the transverse intensity distribution for the individual Stokes beams and to equalize their relative intensities. Full-color holographic imaging is demonstrated with transmitting and reflecting colored objects. Also, the optical noise characteristics of the reconstructed images are investigated.

Journal Article↗

PubMed2003

Four-dimensional microscopy of defects in integrated circuits.

We demonstrate four-dimensional microscopy of defects in integrated circuits by a technique that combines laser-scanning confocal reflectance microscopy with one-photon optical-beam-induced current (1P-OBIC) imaging. Accurate information is obtained about the three-dimensional structure of the defect and the kind of material (metal, semiconductor, or dielectric) that is damaged by the defect. The same focused probe beam simultaneously produces the 1P-OBIC and reflectance signals from the illuminated sample spot. The hardware development cost is minimal for a laser-scanning confocal microscope, and the image reconstruction procedure is computationally efficient. Imaging is demonstrated on defects that are caused by electrical overstress and unwanted generation centers. Exclusive three-dimensional distributions of the semiconductor and metal sites in the integrated circuit reveal defect features that are difficult to recognize with confocal or 1P-OBIC imaging alone.

Journal Article↗

PubMed2003

Self-organized queuing and scale-free behavior in real escape panic.

Numerical investigations of escape panic of confined pedestrians have revealed interesting dynamical features such as pedestrian arch formation around an exit, disruptive interference, self-organized queuing, and scale-free behavior. However, these predictions have remained unverified because escape panic experiments with real systems are difficult to perform. For mice escaping out of a water pool, we found that for a critical sampling rate the escape behavior exhibits the predicted features even at short observation times. The mice escaped via an exit in bursts of different sizes that obey exponential and (truncated) power-law distributions depending on exit width. Oversampling or undersampling the mouse escape rate prevents the observation of the predicted features. Real systems are normally subject to unavoidable constraints arising from occupancy rate, pedestrian exhaustion, and nonrigidity of pedestrian bodies. The effect of these constraints on the dynamics of real escape panic is also studied.

Animals↗

PubMed2003

Primary spherical aberration in two-color (two-photon) excitation fluorescence microscopy with two confocal excitation beams.

We study the effects of primary spherical aberration on the three-dimensional point spread function (PSF) of the two-color (two-photon) excitation (2CE) (2PE) fluorescence microscope with two confocal excitation beams that are separated by an angle theta. The two excitation wavelengths lambda1 and lambda2 are related to the single-photon excitation wavelength lambda(e) by: 1/lambda(e) = 1/lambda1 + 1/lambda2. The general case is considered where both focused beams independently suffer from spherical aberration. For theta = 0, pi/2, and pi, the resulting deterioration of the PSF structure is evaluated for different values of the spherical aberration coefficients via the Linfoot's criteria of fidelity, structural content, and correlation quality. The corresponding degradation of the peak 2CE fluorescence intensity is also determined. Our findings are compared with that of the 2PE fluorescence (lambda1 = lambda2) under the same aberration conditions. We found that the 2CE microscope is more robust against spherical aberration than its 2PE counterpart, with the pi/2 configuration providing the clearest advantage. The prospect of aberration correction in the two-beam 2CE microscope is also discussed.

Journal Article↗

PubMed2002

Radiation force on a nonlinear microsphere by a tightly focused Gaussian beam.

We determine the characteristics of the radiation force that is exerted on a nonresonant nonlinear (Kerr-effect) rigid microsphere by a strongly focused Gaussian beam when diffraction and interference effects are significant (sphere radius a < or = illumination wavelength lambda). The average force is calculated from the surface integral of the energy-momentum tensor consisting of incident, scattered, and internal electromagnetic field vectors, which are expressed as multipole spherical-wave expansions. The refractive index of a Kerr microsphere is proportional to the internal field intensity, which is computed iteratively by the Rytov approximation (residual error of solution, 10(-30). The expansion coefficients for the field vectors are calculated from the approximated index value. Compared with that obtained in a dielectric (linear) microsphere in the same illumination conditions, we find that the force magnitude on the Kerr microsphere is larger and increases more rapidly with both a and the numerical aperture of the focusing objective. It also increases nonlinearly with the beam power unlike that of a linear sphere. The Kerr nonlinearity also leads to possible reversals of the force direction. The proposed technique is applicable to other types of weak optical nonlinearity.

Journal Article↗

PubMed2002

Gravity-assisted segregation of granular materials of equal mass and size.

High-resolution segregation is demonstrated for elastic granular materials of the same mass and size. Each grain starts at a randomly selected position in the entrance facet of a cylinder, accelerates downwards due to gravity, and then bounces against a massive obstacle with a collision cross section that is proportional to the facet size. Bounce dynamics of the falling grain is a function of its relative elasticity with the obstacle. Subsequent collisions of the grain with the wall are assumed to be perfectly elastic. In the absence of interparticle collisions, grain focusing occurs at points along the cylinder axis. In the absence of rotation, focusing occurs regardless of the initial locations and (downward) velocities of the grains at the entrance facet. The focus location depends only on the coefficient of restitution of the falling particle and the obstacle size. Grains arrive at the focus in temporally localized bursts even if released simultaneously from the facet. Efficient segregation is, therefore, achieved without additional mechanical work (e.g., shaking, spinning) on the system configuration.

Journal Article↗

PubMed2002

Noise-driven manifestation of learning in mature neural networks.

We show that the generalization capability of a mature thresholding neural network to process above-threshold disturbances in a noise-free environment is extended to subthreshold disturbances by ambient noise without retraining. The ability to benefit from noise is intrinsic and does not have to be learned separately. Nonlinear dependence of sensitivity with noise strength is significantly narrower than in individual threshold systems. Noise has a minimal effect on network performance for above-threshold signals. We resolve two seemingly contradictory responses of trained networks to noise-their ability to benefit from its presence and their robustness against noisy strong disturbances.

Animals↗

PubMed2002

Reply to comment on "Excitation with a focused, pulsed optical beam in scattering media: diffraction effects.".

We address the issues that were raised by Tycho and Jørgensen [Appl. Opt. 41, 4709 (2002)] concerning our strategy [Appl. Opt. 39, 5244 (2000)] for incorporating the wave properties of light in the description of a propagating focused excitation beam in a highly scattering medium. We explain that the strategy is consistent with the Huygens-Fresnel principle and does not violate the energy conservation principle.

Journal Article↗

PubMed2002

High-contrast images of semiconductor sites via one-photon optical beam-induced current imaging and confocal reflectance microscopy.

We demonstrate a computationally efficient procedure for determining only the semiconductor sites in a confocal reflectance image of an integrated circuit. It utilizes a one-photon optical beam-induced current (1P-OBIC) and confocal reflectance images that are generated from the same focused excitation beam. A 1P-OBIC image is a two-dimensional map of the currents induced by the beam as it is scanned across the circuit surface. A 1P-OBIC is produced by an illuminated semiconductor material if the excitation photon energy exceeds the bandgap. The 1P-OBIC image has no vertical resolution because the 1P-OBIC is linear with the excitation beam intensity. The exclusive high-contrast image of semiconductor sites is generated by the product of the 1P-OBIC image and the confocal image. High-contrast images of the metal sites are also obtained by the product of the complementary OBIC image and the same confocal image.

Journal Article↗

PubMed2002

Behavior of the point-spread function in photon-limited confocal microscopy.

We study the behavior of the point-spread function (PSF) of the confocal scanning optical microscope (CSOM) when the available optical energy density from the sample plane is low (<7.5 microJoule/micrometers2). The PSF profile is analyzed under three photon-limited imaging conditions: (1) reflection-type CSOM with a weak source and a perfectly reflecting sample, (2) reflection-type CSOM with a strong illumination source and a weak sample, and (3) fluorescence CSOM with a weak fluorescent sample. Linfoot's image quality criteria of fidelity, structural content, and correlation quality are used to assess the reproducibility of the PSF profile as a function of the photon number. Low photon numbers yield a PSF profile that is difficult to maintain from one location in the sample plane to another. The optical sectioning capability of the CSOM was found to deteriorate more quickly against light power reduction than its transverse resolving power. The signal-to-noise ratio of the scanned CSOM image improves exponentially with the photon number from the sample plane. The noise that is generated by an unstable PSF has an average amplitude that decreases exponentially with the photon number and is significant only at low photon numbers. The CSOM image quality deteriorates because of spurious high-frequency components, degradation in the PSF dynamic range, and varying resolving power.

Journal Article↗

PubMed2002

Emergence of hysteresis in a network of nonhysteretic agents with continuous responses.

We model the emergence of hysteresis as a collective behavior in a lattice network of individually nonhysteretic agents with continuous responses. The emergence, which depends on the agent's characteristic response to an external input, is optimized at a finite interaction size of the Moore neighborhood. The network also exhibits rich behavior including power-law variations, chaos, and system saturation. Our model is used to describe the hysteresis and high-frequency fluctuations in the oxygen isotope variation ( delta18O) data of ice (Greenland Ice Core Project) that exhibit the Younger Dryas cold event.

Models, Biological↗