Observation of viscous liquid flow in tobacco substrate during heating using optical coherence tomography.

The present study used optical coherence tomography (OCT) to monitor the dynamics of a highly viscous liquid in a porous tobacco substrate during heating. The OCT technique was integrated with a specially designed heating chamber and an air pump for measuring. Two transitional points in the liquid behaviours at different temperatures were estimated using OCT and statistical analysis of the attenuation coefficient. The first point, 'A', shows the time approximation at which the penetration-dominant zone transitions into the evaporation-dominant zone. The second point, 'B', indicates the time approximation at which rapid evaporation of free liquid transitions into slow evaporation of trapped and bound liquid. This analytical system is an alternative for tracking liquid transport in porous biomass during heating.

Formation of a Giant Anisotropically Ordered Assembled Structure of Inorganic Nanosheets through an Optically Induced Stream.

Formation of a desirable submillimeter-scaled assembled structure of particles in the colloid is a difficult subject in colloidal chemistry. Herein, a submillimeter-scaled ordered assembled structure consisting of highly anisotropic two-dimensional plate-like particles, niobate nanosheets, was obtained through an optical manipulation technique that was assisted by a scattering-force-induced stream. A 532 nm continuous wave laser beam with a power of 400 mW was used to illuminate a liquid crystalline niobate nanosheet colloid from the bottom side of a sample cell, inducing the stream of oriented nanosheets toward the upper side of the sample cell. As a result, a 200 µm ordered assembled structure consisting of oriented nanosheets was formed. The assembled structure was also characterized by two-dimensional anisotropy, reflecting that the highly anisotropic morphologies of each nanosheet and the shape of that structure were dependent on the polarization of incident illumination. This study has revealed a new noncontact and on-demand way to obtain submillimeter-scaled ordered anisotropic colloidal assembled structures of nanosized particles such as nanosheets, contributing to fundamental materials science and expanding the utilities of nanosheets.

Spectral noise reduction and temporal coherence control using a phase unsynchronized wave synthesizing method.

Highly accurate spectrometry requires spectral noise reduction. In this paper, we propose a phase unsynchronized wave synthesizing (PuwS) method that provides different optical path lengths for different wave elements obtained from the division of a wavefront and synthesizes the respective wave elements to have the same propagation direction. PuwS achieves spectral noise reduction and contributes to temporal coherence control. To confirm these properties observed in experimental data, we propose a series of analytical models based on a traditional wave train model. According to the analytical model, PuwS generates an ensemble average effect that prevents spectral noise and decreases the visibility of the spectral fringe pattern. The experimental data show that the spectral noise is reduced when the total number of wave elements increases. PuwS is found to drastically change the measured spectral profile of a silk sample, achieving highly accurate spectrometry. The data also show that a combination of PuwS and an appropriate diffuser decreases the spectral visibility regarding the temporal coherence more effectively than a conventional method using one or more diffusers.

Microscope Observation of Morphology of Colloidally Dispersed Niobate Nanosheets Combined with Optical Trapping.

Although inorganic nanosheets prepared by exfoliation (delamination) of layered crystals have attracted great attention as 2D nanoparticles, in situ real space observations of exfoliated nanosheets in the colloidally dispersed state have not been conducted. In the present study, colloidally dispersed inorganic nanosheets prepared by exfoliation of layered niobate are directly observed with bright-field optical microscopy, which detects large nanosheets with lateral length larger than several micrometers. The observed nanosheets are not strictly flat but rounded, undulated, or folded in many cases. Optical trapping of nanosheets by laser radiation pressure has clarified their uneven cross-sectional shapes. Their morphology is retained under the relation between Brownian motion and optical trapping.

Burn depth assessments by photoacoustic imaging and laser Doppler imaging.

Diagnosis of burn depths is crucial to determine the treatment plan for severe burn patients. However, an objective method for burn depth assessment has yet to be established, although a commercial laser Doppler imaging (LDI) system is used limitedly. We previously proposed burn depth assessment based on photoacoustic imaging (PAI), in which thermoelastic waves originating from blood under the burned tissue are detected, and we showed the validity of the method by experiments using rat models with three different burn depths: superficial dermal burn, deep dermal burn and deep burn. On the basis of those results, we recently developed a real-time PAI system for clinical burn diagnosis. Before starting a clinical trial, however, there is a need to reveal more detailed diagnostic characteristics, such as linearity and error, of the PAI system as well as to compare its characteristics with those of an LDI system. In this study, we prepared rat models with burns induced at six different temperatures from 70 to 98 °C, which showed a linear dependence of injury depth on the temperature. Using these models, we examined correlations of signals obtained by PAI and LDI with histologically determined injury depths and burn induction temperatures at 48 hours postburn. We found that the burn depths indicated by PAI were highly correlative with histologically determined injury depths (depths of viable vessels) as well as with burn induction temperatures. Perfusion values measured by LDI were less correlative with these parameters, especially for burns induced at higher temperatures, being attributable to the limited detectable depth for light involving a Doppler shift in tissue. In addition, the measurement errors in PAI were smaller than those in LDI. On the basis of these results, we will be able to start clinical studies using the present PAI system.

Real-time photoacoustic imaging system for burn diagnosis.

We have developed a real-time (8 to 30 fps) photoacoustic (PA) imaging system with a linear-array transducer for burn depth assessment. In this system, PA signals originating from blood in the noninjured tissue layer located under the injured tissue layer are detected and imaged. A compact home-made high-repetition-rate (500 Hz) 532-nm fiber laser was incorporated as a light source. We used an alternating arrangement for the fibers and sensor elements in the probe, which improved the signal-to-noise ratio, reducing the required laser energy power for PA excitation. This arrangement also enabled a hand-held light-weight probe design. A phantom study showed that thin light absorbers embedded in the tissue-mimicking scattering medium at depths >3 mm can be imaged with high contrast. The maximum error for depth measurement was 140 µm. Diagnostic experiments were performed for rat burn models, including superficial dermal burn, deep dermal burn, and deep burn models. Injury depths (zones of stasis) indicated by PA imaging were compared with those estimated by histological analysis, showing discrepancies 200 µm. The system was also used to monitor the healing process of a deep dermal burn. The results demonstrate the potential usefulness of the present system for clinical burn diagnosis.

Spectroscopic study on appearances of make-up skins using a visible RGB-LED OCT.

BACKGROUND/PURPOSE: Facial foundation is very effective to correct color irregularities of the skin surface and to protect the skin from harmful light. This depends strongly on both the optical properties and the coating condition of foundation on the skin surface. METHODS: We constructed the full-field optical coherence tomography (OCT) (FF-OCT) microscope with visible light sources of RGB LEDs. The commercially available skin replicas were used as the model of skin in the experiment, which were composed of two layers, a thin polyurethane film transcribed from cheek surface of a female and a beige-colored silicone substrate. The foundations were applied to the skin replicas under the constant pressure. RESULTS: A topographic image provides spectroscopic information of reflected light and effectiveness of correction of surface irregularities by applying the foundation. A tomographic image demonstrates the spectroscopic degree of light penetration into the skin tissue. It is shown that the reflectivity increases consistently with thickness of the applied foundation because light reflected from the surface and diffusively reflected from the inside of the tissue increases as the surface becomes flat applying the foundation. CONCLUSION: We confirmed experimentally the potential of the spectroscopic FF-OCT microscopy in investigating both qualitatively and quantitatively the effectiveness of facial foundation.

Optical coherence tomography using images of hair structure and dyes penetrating into the hair.

BACKGROUND/PURPOSE: Hair dyes are commonly evaluated by the appearance of the hair after dyeing. However, this approach cannot simultaneously assess how deep the dye has penetrated into hair. METHODS: For simultaneous assessment of the appearance and the interior of hair, we developed a visible-range red, green, and blue (RGB) (three primary colors)-optical coherence tomography (OCT) using an RGB LED light source. We then evaluated a phantom model based on the assumption that the sample's absorbability in the vertical direction affects the tomographic imaging. RESULTS: Consistent with theory, our device showed higher resolution than conventional OCT with far-red light. In the experiment on the phantom model, we confirmed that the tomographic imaging is affected by absorbability unique to the sample. Furthermore, we verified that permeability can be estimated from this tomographic image. We also identified for the first time the relationship between penetration of the dye into hair and characteristics of wavelength by tomographic imaging of dyed hair. CONCLUSION: We successfully simultaneously assessed the appearance of dyed hair and inward penetration of the dye without preparing hair sections.

Low-coherence dynamic light scattering and its potential for measuring cell dynamics.

Fluorescence correlation spectroscopy is a powerful technique for studying the structures and dynamics of living cells. Dynamic light scattering (DLS) is also used to study dynamic characteristics and it has the potential to measure cell dynamics. However, it is difficult to apply DLS to highly scattering media. In this article, we review low-coherence dynamic light scattering (LC-DLS). It strongly suppresses the influence of multiple scattering and has a greater potential for measuring cell dynamics than conventional DLS. The properties of LC-DLS are described theoretically and experimentally. Measurement of the diffusion coefficients of macromolecules in turbid media and interparticle and molecular interactions by LC-DLS is demonstrated.

Highly controllable optical tweezers using dynamic electronic holograms.

Dielectric particles including living cells are trapped within focused laser beam spots, and as a result, they can be transferred by displacing the beam spots. Such the particle manipulating technique is called optical tweezers. Holographic optical tweezers (HOT) enables highly flexible and precise control of particles, introducing holography technique to them. HOT is one of the most expected techniques for investigations of cell-cell signaling which require precise arraying of living cells. We had developed a new highly controllable HOT system where two different intensity patterns, a carrier beam spot and a beam array, are generated quasi-simultaneously by time-division multiplexing. Particles are transferred to the beam array by the carrier beam spot displaced in real time by phase shifting of holograms. In this review, we introduce our work, the construction of the system, demonstration of manipulating particles and investigations of the spatio- temporal stability of trapped particles in our system.

Hydrodynamic measurement of Brownian particles at a liquid-solid interface by low-coherence dynamic light scattering.

The hydrodynamics of Brownian particles close to a wall is investigated using low-coherence dynamic light scattering. The diffusion coefficient of the particles in a suspension is measured as a function of distance from the wall. A sudden reduction in the diffusion coefficient near the interface is clearly observed using this method. The theoretically predicted wall-drag effect is experimentally confirmed when the influence of the spatial resolution due to the finite coherence length of the light source is accounted for. The space-dependent dynamics of Brownian particles under the wall-drag effect is obtained for the first time using our spatially resolved dynamic light scattering technique.

Numerical analysis of a path-length-resolved spectrum of time-varying scattered light field.

The path-length-resolved power spectrum of a time-varying scattered light field measured by a time-of-flight method or low-coherence interferometry is evaluated by a new numerical simulation algorithm. The path-length-resolved power spectrum is theoretically derived by combining diffusing-wave-spectroscopy theory and radiative-transfer theory. The proposed algorithm, using the Monte Carlo method, is used to determine the scattering configurations and numerically calculate the power spectrum. The path-length distribution, path-length-dependent scattering order distribution, and path-length-resolved power spectrum are demonstrated numerically over all scattering orders. The resultant power spectra agree with experimental results measured by the low-coherence-dynamic-light-scattering method.

Single-scattering spectroscopy for extremely dense colloidal suspensions by use of a low-coherence interferometer.

Single-scattering spectroscopy by use of a low-coherence interferometer is introduced to measure the power spectra of light scattered from extremely dense colloidal suspensions. The power spectrum of a heterodyne component can be obtained by subtraction of the power spectrum of a homodyne component from the measured power spectrum. The heterodyne power spectrum for light scattered from the medium is shown to coincide with the single-scattering spectrum to a depth of up to a few times the mean-free path length. Therefore single-scattering spectroscopy is newly proposed as a means by which to analyze the characteristics of extremely dense colloidal suspensions.