Optical Signal Response Research Articles

Design and Fabrication of Silcon Microlens with Low SAG for 528(H) � 528(V) Infrared Charge-Coupled Device Application

Microlens array is an important optical element to improve the photosensitivity of charge-coupled device (CCD). In this paper, a monolithic integration technology between microlens and 528 × 528 element PtSi Schottky-barrier infrared charge-coupled device (IRCCD) with a pixel size of 30μm × 30μm has been developed. The microlens array with low sag and long focal length is designed based on geometrical optics theory. It is directly formed on the back side of the substrate in IRCCD chip using successive photolithography and A+ ion beam etching (IBE) technology. The microlens array is characterized by both surface stylus and point spread function (PSF). The experiment results of integration device between IRCCD and microlens array indicate that the optical signal response is improved obviously and a responsivity increase by a factor of 1.8 in the operation band.

Chemotopic Arrangement for Taste Quality Discrimination in the Cortical Taste Area

Signals from various sensory organs are delivered to the brain where sensory information is generated from the signals. The information is represented on the brain in the form of temporal and spatial codes, which enable us to create inner an representation of the outer world (Florey, 1990). In the neocortex, the information consisting of the spatial codes is principally arranged in the primary sensory area as a receptive field, by way of anatomical column formation. The information consisting of temporal codes, such as frequency and phase dynamics, also plays an important role for synchronization of neural activities or strengthening signal amplitudes. Interaction or integration of the information by way of intra-cortical or cortico-cortical connections enables the temporal and spatial codes to link (Singer and Gray, 1995; Gilbert et al., 1996; Salinas and Sejnowski, 2001). As for taste information processing, controversy still exists as to whether cortical taste neurons use temporal codes or spatial codes for discriminating taste information in the cortical taste area. However, it may be presumed that cortical taste neurons use spatial codes as well as frequency codes in order to discriminate taste information efficiently. Previous electrophysiological studies predict that there is a chemotopic arrangement for taste quality discrimination in the cortical taste area, but this hypothesis has not been confirmed because of lacking for the evidence with high resolution of spatial dimension. Optical imaging based on intrinsic signals has a high spatial resolution (Frostig et al., 1990) and is useful for studying the functional organization of the brain (Bonhoeffer and Grinvald, 1996). Here, we investigated the spatial aspects of optical intrinsic signal (OIS) responses in the gustatory insular cortex that were elicited by delivering a solution of tastants on the tongue.

Second harmonic generation in In 2O 3–SiON films doped by Al and Sn

Photoinduced optical and second-order non-linear optical effects in the interfaces separating In 2O 3–SiON (O/N ratio equals 1) films doped with A1, Sn and glass substrates were investigated using the photoinduced optical second harmonic generation. The photoinduced effective second-order optical susceptibility d eff (at λ=1.76 μm ) shows a good correlation with the linear optical susceptibility, particularly with the shift of the absorption edge. The maximal response of the photoinduced optical response signal was observed for the pump–probe delaying time of 34 ps . The performed experimental measurements indicate that the observed effects are mainly caused by the interface potential gradients on the border glass–In 2O 3–SiON film and by additional polarization due to insertion of the Al and Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigation of thin semiconducting interfacial layers and simultaneously such films may be used as materials for non-linear optical devices.

Cortical spatial aspects of optical intrinsic signals in response to sucrose and NaCl stimuli.

To examine whether cortical taste neurons use spatial codes for discriminating taste information, we investigated the spatial aspects of optical intrinsic signal (OIS) responses in the gustatory insular cortex (GC) elicited by the administration of two essential tastants, sucrose and NaCl, on the tongue. OIS responses to sucrose appeared in the rostral part of the GC, whereas those to NaCl appeared in the central part of the GC. Local anesthetization of the tongue abolished OIS responses, and the administration of distilled water elicited no OIS response. Thus, taste information elicited by sucrose and NaCl from the peripheral sensory organs is segregated in the GC, suggesting that the information from two essential tastants is assembled as spatial codes in the primary cortical taste area through the process of taste quality perception.

Imaging spatio-temporal patterns of long-term potentiation in mouse hippocampus.

Spatio-temporal patterns of neuronal activity before and after the induction of long-term potentiation in mouse hippocampal slices were studied using a real-time high-resolution optical recording system. After staining the slices with voltage-sensitive dye, transmitted light images and extracellular field potentials were recorded in response to stimuli applied to CA1 stratum radiatum. Optical and electrical signals in response to single test pulses were enhanced for at least 30 minutes after brief high-frequency stimulation at the same site. In two-pathway experiments, potentiation was restricted to the tetanized pathway. The optical signals demonstrated that both the amplitude and area of the synaptic response were increased, in patterns not predictable from the initial, pretetanus, pattern of activation. Optical signals will be useful for investigating spatio-temporal patterns of synaptic enhancement underlying information storage in the brain.

Temporally staggered forelimb stimulation modulates barrel cortex optical intrinsic signal responses to whisker stimulation.

Characterization of neurovascular relationships is critical to accurate interpretation of functional neuroimaging data. We have previously observed spatial uncoupling of optical intrinsic signal imaging (OIS) and evoked potential (EP) responses in rodent barrel cortex following simultaneous whisker and forelimb stimulation, leading to changes in OIS response magnitude. To further test the hypothesis that this uncoupling may have resulted from "passive" overspill of perfusion-related responses between functional regions, we conducted the present study using temporally staggered rather than simultaneous whisker and forelimb stimulation. This paradigm minimized overlap of neural responses in barrel cortex and forelimb primary somatosensory cortex (SI), while maintaining overlap of vascular response time courses between regions. When contrasted with responses to 1.5-s lone-whisker stimulation, staggered whisker and forelimb stimulation resulted in broadening of barrel cortex OIS response time course in the temporal direction of forelimb stimulation. OIS response peaks were also temporally shifted toward the forelimb stimulation period; time-to-peak was shorter (relative to whisker stimulus onset) when forelimb stimulation preceded whisker stimulation and longer when forelimb stimulation followed whisker stimulation. In contrast with OIS and EP magnitude decreases previously observed during simultaneous whisker/forelimb stimulation, barrel cortex OIS response magnitude increased during staggered stimulation and no detectable changes in underlying EP activity were observed. Spatial extent of barrel cortex OIS responses also increased during staggered stimulation. These findings provide further evidence for spatial uncoupling of OIS and EP responses, and emphasize the importance of temporal stimulus properties on the effects of this uncoupling. It is hypothesized that spatial uncoupling is a result of passive overspill of perfusion-related responses into regions distinct from those which are functionally active. It will be important to consider potential influences of this uncoupling when designing and interpreting functional imaging studies that use hemodynamic responses to infer underlying neural activity.

Multichannel digital transmission in an optical network of communicating molecules.

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.

Optical response of planar Mo/n-Si/Mo structures with long neutral region and Schottky barriers at both ends

Influence of neutral region on the low frequency (100 Hz to 1 MHz) optical signal response of planar molybdenum/n-type silicon/molybdenum structures with Schottky barriers at both ends has been investigated. It is found that the presence of the neutral region under optical illumination can enhance the device signal current and the spectrum of increment in the signal current exhibits a low turn-over frequency due to its diffusion mechanism. An equivalent circuit representation of such a structure has also been proposed.

Analysis of optical signals evoked by peripheral nerve stimulation in rat somatosensory cortex: dynamic changes in hemoglobin concentration and oxygenation.

The origins of reflected light changes associated with neuronal activity (optical signals) were investigated in rat somatosensory cortex with optical imaging, microspectrophotometry, and laser-Doppler flowmetry, and dynamic changes in local hemoglobin concentration and oxygenation were focused on. Functional activation was carried out by 2-second, 5-Hz electrical stimulation of the hind limb under chloralose anesthesia. These measurements were performed at the contralateral parietal cortex through a thinned skull. Regional cortical blood flow (rCBF) started to rise 1.5 seconds after the stimulus onset, peaked at 3.5 seconds (26.7% +/- 9.7% increase over baseline), and returned to near baseline by 10 seconds. Optical signal responses at 577, 586, and 805 nm showed a monophasic increase in absorbance coincident with the increase in rCBF; however, the signal responses at 605 and 760 nm were biphasic (an early increase and late decrease in absorbance) and microanatomically heterogeneous. The spectral changes of absorbance indicated that the concentrations of both total hemoglobin and oxyhemoglobin increased together with rCBF; deoxyhemoglobin, increased slightly but distinctly (P = 0.016 at 1.0 seconds, P = 0.00038 at 1.5 seconds) just before rCBF increases, then decreased. The authors conclude that activity-related optical signals are greatly associated with a moment-to-moment adjustment of rCBF and metabolism to neuronal activity.

Unusual Photon Energy Dependence of the Cooper Pair Breaking Rate in YBa2Cu3O7−δ Epitaxial Thin Films

The transient photoimpedance response of epitaxial YBa2Cu3O7−δ thin films has been studied using 100 fs Ti:Sapphire laser pulse excitation. Both temperature and photon energy dependence of the fast optical response signal (whose temperature dependence can be explained by a kinetic inductance model involving Cooper pair breaking) were studied. The pair breaking rate is strongly photon energy-dependent, with a resonance around 1.5 eV with a width of only 100 meV, which is very surprising given the strong electron correlation in this metallic system and may be explained in terms of the stripe phase model.

Picosecond pulse induced NLO response of fullerene glass

Picosecond-degenerate-four-wave-mixing (ps-DFWM) experiments have been performed on C 60 C 70 doped high- T m (melting-temperature) phosphate glass. The observed NLO optical response signal at zero delay fades away with increasing fullerene content. Meanwhile, it is broadened by a post-peak shoulder which decays with a characteristic lifetime of ∼ 0.3 ns. The shoulder is attributed to the excited state population grating produced by excitation S 0 → S 1 of fullerene, followed by a predominant nonradiative decay. The crossing transition from the singlet S 1 to the triplet metastable T 1 state is secondary, giving rise to a weak luminescence at 825 nm. On a nanosecond time scale a periodic laser-induced acoustic phonon signal observed can be used to verify that the doping status of large fullerene molecules in inorganic vitreous state after undergoing a melting process at 1200 °C remains undestroyed.

Effect of KTa 1− xNb xO 3 crystal orientation on the nonlinear optical response in the picoseconds degenerate-four-wave mixing

Nonlinear optical response signals on picosecond and nanosecond time scales have been studied in the mixed-crystal system KTa 1− x Nb x O 3 using transient degenerate-four-wave mixing (DFWM). The two distinct signal components, denoted as an instantaneous response (IR) and slow response (SR) in previous studies, changed intensity as the relative arriving time between two write pulses varied. The dependence of these signals on the crystal orientation was characterized. The results were consistent with a lattice relaxation model based on the laser-induced dynamic displacement of the Nb ion. In this model the signal variations result from the competition between the dynamic displacement and the intrinsic distortion associated with the spontaneous polarization along the optic axis.

Excitation migration in Cr-doped fosterite crystals

Using picosecond YAG-laser in a DFWM experiment the broadening of the instantaneous optical response signal has been identified as the evidence of the excitation migration from the impurity Cr 3+ ions to the lasing Cr 4+ ions. The time interval for energy transfer was found to be ∼ 55 ps.

Linearity considerations in quantitative thin-layer chromatography

The relationship between the densitometric response of thin-layer chromatography (TLC) and the quantity of separated substance contained in a particular spot is discussed. Attention is focused upon remittance measurements. The relationship between the optical response signal and the concentration of the substance is highly non-linear. The quantity of substance contained in a particular spot is obtained by integration of the linearized spot signal over the area of the spot, an operation which requires a linear relation between optical signal and concentration. Transform equations which achieve approximate linearity over a wide range of concentrations are developed with modified solutions to the Kubelka and Munk equations as basis. The design possibilities for (flying) point scanners are briefly discussed. The need to obtain a baseline (surface) by algorithmic processing and the remaining plate noise are discussed as the ultimate limitation to the performance of the point scanning devices. Dual-wavelength scanning is able to reduce substantially both problems. The principles of quantitation are then discussed and the possibility of substituting the reading of peak values for integration. A comparative analysis of slit scanning versus point scanning is made.

Optical measurements on scattering media for biomedical applications

The topics of this paper are some theoretical questions relating to the use of photometric measurements on turbid media, for determining the concentration of mostly selectively absorbing substances diffusely contained in the latter. Emphasis is placed on aspects relevant to common biomedical applications. The starting point is the well known theory of Kubelka and Munk. Its equation are used in a modified form, derived from a previously developed electrical model of the optical case. It is shown that the wanted concentration values are obtained by inverting the difference (or the ratio) of the optical response signals of the examined sample and of the blank medium. The relative advantages of measurements in the transmittance and reflectance modes are briefly discussed.