Midinfrared modulation through the use of field-induced scattering in ferroelectric liquid crystals

The feasibility of the use of modulation devices based on field-induced transient scattering in ferroelectric liquid crystals (LC) to replace mechanical choppers used in uncooled infrared-imaging systems was investigated. Devices fabricated with ITO-coated ZnSe substrates and a ferroelectric LC path length of 25 μm were able to modulate optical radiation by transient forward scattering at rates approaching 20 kHz. Through the use of a commercial arbitrary waveform generator and associated PC-based software, drive waveforms were developed that produced a variable, square-wave optical-modulation pattern by the extension of the duration of the scattering state to periods ranging from hundreds of microseconds to milliseconds. The ability of these extended-scattering-mode (ESM) devices to modulate radiation in both the visible and midinfrared regions was verified in a simple experiment through the use of a Fourier-transform infrared spectrometer, in which an unoptimized ESM device displayed a 40% modulation dep th for IR radiation in the 8-12-μm region.     

Visible and near-ultraviolet absorption spectrum of ice from transmission of solar radiation into snow

Snow is a scattering-dominated medium whose scattering is independent of wavelength at 350-600 nm. The attenuation of solar radiation in snow can be used to infer the spectral absorption coefficient of pure ice, by reference to a known value at 600 nm. The method is applied to clean Antarctic snow; the absorption minimum is at 390 nm, and the inferred absorption coefficient is lower than even the lowest values of the Antarctic Muon and Neutrino Detector Array (AMANDA) experiment on glacier ice: The absorption length is at least 700 m, by comparison with 240 m for AMANDA and 10 m from laboratory attenuation measurements.     

Spectral dependence of the scattering coefficient in case 1 and case 2 waters

An approximate linear relationship between the scattering coefficient and the wavelength of light in the visible is found in case 1 and case 2 waters. From this relationship, we estimate scattering at an unknown wavelength from scattering at a single measured wavelength. This approximation is based on measurements in a 1.5-m-thick surface layer collected with an AC9 instrument at 63 stations in the Arabian Sea, northern Gulf of Mexico, and coastal North Carolina. The light-scattering coefficient at 412 nm ranged from 0.2 to 15.1 m(-1) in these waters, and the absorption coefficient at 412 nm ranged from 0.2 to 4.0 m(-1). A separate data set for 100 stations from Oceanside, California, and Chesapeake Bay, Virginia, was used to validate the relationship. Although the Oceanside waters were considerably different from the developmental data set (based on absorption-to-scattering ratios and single-scattering albedos), the average error between modeled and measured scattering values was 6.0% for the entire test data set over all wavelengths (without regard to sign). The slope of the spectral scattering relationship decreases progressively from high-scattering, turbid waters dominated by suspended sediments to lower-scattering, clear waters dominated by phytoplankton.     

Near-infrared light propagation in an adult head model. I. Modeling of low-level scattering in the cerebrospinal fluid layer

Adequate modeling of light propagation in a human head is important for quantitative near-infrared spectroscopy and optical imaging. The presence of a nonscattering cerebrospinal fluid (CSF) that surrounds the brain has been previously shown to have a strong effect on light propagation in the head. However, in reality, a small amount of scattering is caused by the arachnoid trabeculae in the CSF layer. In this study, light propagation in an adult head model with discrete scatterers distributed within the CSF layer has been predicted by Monte Carlo simulation to investigate the effect of the small amount of scattering caused by the arachnoid trabeculae in the CSF layer. This low scattering in the CSF layer is found to have little effect on the mean optical path length, a parameter that can be directly measured by a time-resolved experiment. However, the partial optical path length in brain tissue that relates the sensitivity of the detected signal to absorption changes in the brain is strongly affected by the presence of scattering within the CSF layer. The sensitivity of the near-infrared signal to hemoglobin changes induced by brain activation is improved by the effect of a low-scattering CSF layer.     

Characterization of Si nanowaveguide line edge roughness and its effect on light transmission

The manufacture of low-loss silicon-on-insulator (SOI) photonic wires for telecommunication wavelengths (∼1.55 μm) is a challenge. Side wall and line edge roughness (LER) are the dominant sources of scattering loss. In this work the characterization of Si nanowaveguide (NW) LER was performed and its effect on light transmission was theoretically analyzed and measured. NW structures with a width of 0.5 μm and height of 0.22 μm were prepared using different thickness of hard-mask and plasma etch process technologies on SOI platforms. LER determination was performed by critical-dimension scanning electron microscope (CD-SEM), conventional atomic force microscope (AFM) and 3D-AFM. The characterization of LER quality was carried out by monitoring of its RMS deviation σ, main frequencies and correlation length L_c. The effect of sampling length was evaluated. The data for σ from 0.8 to 6 nm and L_c from 20 to 50 nm were found to be dependent mostly on etch process technology. Theoretical simulation of scattering loss due to LER based on the 2D analytical model for planar waveguides was performed. Finally, the correlation between NW optical transmission (scattering) losses (TL) and LER was obtained and can be applied to future technology development. Especially for the case of σ ∼ 0.85 nm and L_c ∼ 20 nm the lowest value of TL ∼ 1.2 dB/cm was measured at a wavelength of 1.55 μm. Good qualitative agreement between calculated and measured losses due to LER was found.     

Scatter correction of transmission near-infrared spectra by photon migration data: quantitative analysis of solids

The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model.     

Graphene oxide (GO)-based wideband optical polarizer using a non-adiabatic microfiber

In this paper, a microfibre polarizer based on graphene oxide (GO) is proposed and demonstrated. A microfibre was coated with GO using the drop-casting technique. The extinction ratio (ER) has been measured at wideband range of 1310, 1460, 1550 and 1600 nm. The highest ER obtained in this experiment was 37.0 dB measured at 1480 nm wavelength. The result has been achieved with a GO coating thickness of 24 μm and coating length of 12 mm. This work demonstrates a polarizing effect of GO-coated microfibre.     

Nature of light scattering in dental enamel and dentin at visible and near-infrared wavelengths

The light-scattering properties of dental enamel and dentin were measured at 543, 632, and 1053 nm. Angularly resolved scattering distributions for these materials were measured from 0° to 180° using a rotating goniometer. Surface scattering was minimized by immersing the samples in an index-matching bath. The scattering and absorption coefficients and the scattering phase function were deduced by comparing the measured scattering data with angularly resolved Monte Carlo light-scattering simulations. Enamel and dentin were best represented by a linear combination of a highly forward-peaked Henyey-Greenstein (HG) phase function and an isotropic phase function. Enamel weakly scatters light between 543 nm and 1.06 μm, with the scattering coefficient (μ(s)) ranging from μ(s) = 15 to 105 cm(-1). The phase function is a combination of a HG function with g = 0.96 and a 30-60% isotropic phase function. For enamel, absorption is negligible. Dentin scatters strongly in the visible and near IR (μ(s)?260 cm(-1)) and absorbs weakly (μ(a) ? 4 cm(-1)). The scattering phase function for dentin is described by a HG function with g = 0.93 and a very weak isotropic scattering component (? 2%).     

Reduction in the thermal conductivity of single crystalline silicon by phononic crystal patterning

Phononic crystals (PnCs) are the acoustic wave equivalent of photonic crystals, where a periodic array of scattering inclusions located in a homogeneous host material causes certain frequencies to be completely reflected by the structure. In conjunction with creating a phononic band gap, anomalous dispersion accompanied by a large reduction in phonon group velocities can lead to a massive reduction in silicon thermal conductivity. We measured the cross plane thermal conductivity of a series of single crystalline silicon PnCs using time domain thermoreflectance. The measured values are over an order of magnitude lower than those obtained for bulk Si (from 148 W m(-1) K(-1) to as low as 6.8 W m(-1) K(-1)). The measured thermal conductivity is much smaller than that predicted by only accounting for boundary scattering at the interfaces of the PnC lattice, indicating that coherent phononic effects are causing an additional reduction to the cross plane thermal conductivity.     

Experimental investigation of the cooling performance of a ground source heat pump system in Denizli, Turkey

The ground source heat pump system (GSHP) is installed at PamukkaleUniversity in Denizli, Turkey. The U-bend ground heat exchanger pipe length of 225 m was buried in soil at 110 m depth. In the 2008 cooling season, performance coefficients of the heat pump and the system were determined in the range of 3.1-4.8 and 2.1-3.1, respectively. The values of solar radiation, external temperature, relative humidity and wind speed were measured continuously. The relations of performance coefficients of ground source heat pump according to the meteorological data including solar radiation, wind speed, relative humidity and external temperature with this experiment were revealed exactly. The results of this study fulfil the lack in the literature.     

Measurement of the Coherent Neutron Scattering Length of 3He

By means of neutron interferometry the s-wave neutron scattering length of the ³He nucleus was re-measured at the Institut Laue-Langevin (ILL). Using a skew symmetrical perfect crystal Si-interferometer and a linear twin chamber cell, false phase shifts due to sample misalignment were reduced to a negligible level. Simulation calculations suggest an asymmetrically alternating measuring sequence in order to compensate for systematic errors caused by thermal phase drifts. There is evidence in the experiment’s data that this procedure is indeed effective. The neutron refractive index in terms of Sears’ exact expression for the scattering amplitude has been analyzed in order to evaluate the measured phase shifts. The result of our measurement, b′_c = (6.000 ± 0.009) fm, shows a deviation towards a greater value compared to the presently accepted value of b′_c = (5.74 ± 0.07) fm, confirming the observation of the partner experiment at NIST. On the other hand, the results of both precision measurements at NIST and ILL exhibit a serious 12σ (12 standard uncertainties) deviation, the reason for which is not clear yet.     

Scattering of ultrasound from skeletal muscle tissue

The purpose of this work was to explore the mechanisms which are responsible for the scattering of ultrasound from skeletal muscle tissue. It was undertaken in response to an interesting phenomenon observed in the authors' laboratory whereby scattering power from avian skeletal muscle changed in concordance with passive stretch. Ultrasonic scattering from skeletal muscle samples was measured as they were stretched passively in increments of 10% of their original length up to 40%. The samples were illuminated with an ultrasound beam from a transducer which was oriented orthogonally to and at 20 degrees from the normal to the long axis of the muscle sample. It was found that the integrated backscatter increased significantly over the strain range for the orthogonal orientation, but it changed very little after the initial stretch when the orientation was 20 degrees . It is postulated that this phenomenon may be caused by reorientation of the endomysial collagen fibers surrounding each muscle fiber.     

Optical sizing of immunolabel clusters through multispectral plasmon coupling microscopy

The wavelength dependent scattering cross sections of self-assembled silver nanoparticle clusters of known size (n) were measured on five different wavelength channels between 427 and 510 nm through correlation of multispectral imaging and scanning electron microscopy. A multivariate statistical analysis of the spectral response of this training set provided a correlation between spectral response and cluster size and enabled a classification of new measurements into four distinct nanoparticle association levels (I1-I4) whose compositions were dominated by monomers (I1), dimers (I2), trimers and tetramers (I3), and larger clusters (I4), respectively. One potential application of the optical sizing approach is to map association levels of silver immunolabels on cellular surfaces. We demonstrate the feasibility of this approach using silver immunolabels targeted at the epidermal growth factor receptor on A431 cells in a proof of principle experiment. The ability to measure immunolabel association levels on subcellular length scales in an optical microscope provides new opportunities for experimentally assessing receptor density distributions on living cells in solution.     

Measurement of the point-spread function in a layered system

A laboratory facility to measure the point-spread function (PSF) of water with the addition of scattering layers is described. The PSF was measuredby using an approximately Lambertian source and a camera that viewed this source but focused at infinity. Measurements for various optical path lengths with the scattering layer in three separate regions, i.e., near the source, near the camera, and an intermediate case, were performed. The PSF was found to depend strongly on the location of the scattering layer. For the same optical path length, the most diffuse PSF was found for the case of a scattering layer near the camera.     

单根沥青基炭纤维热导率的温度特性研究

采用"T"形法测量了温度100K～400K范围内单根沥青基炭纤维的热导率.结果表明,在300K以下,由于边界散射的影响,炭纤维热导率随着温度升高而增大,350K左右渐趋于饱和,对应热导率约为800W/(in·K),400K附近热导率又增大至920W/(in·K).在不改变接触点的前提下,通过测量同一根纤维小同长度对应的热导率,估计了炭纤维与热线节点处的接触热阻,并讨论了不同温度下辐射对热导率测量的影响,最后得到热导率的测量不确定度在±13%以内.     

Experimental measuring of the coherence length of a single photon generated via a degenerated optical parametric oscillator far below threshold

In this work, we report on experimental measuring of the coherence length of a single photon, which is generated via a degenerated optical parametric oscillator (OPO) operated far below threshold. Although the bandwidth of the OPO cavity is about 7.8 MHz, the measured coherence length of the single photon is only about 90 µm via a Michelson interferometer, due to the multimode property of the photon generated in the experiment. Therefore, further reducing the bandwidth of the photon is necessary for its application in some fields, such as transferring the information between the photon and an atomic system.     

Atomic structure display of a real silicon surface under light scattering

Angular dependencies of the scattered light intensity were measured on Si wafers that have different crystallographic orientations by using a He-Ne laser (λ = 632.8 nm, 80 μm spot diameter). During the experiment the Si wafer was fixed relative to the incident beam. Regular patterns were found in the azimuthal-angle-resolved scattering curves. Such patterns seem to be caused by the faceted shallow atomic structures of the surface.     

In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry

Methods for local photon path length and optical properties estimation, based on measured and simulated diffuse reflectance within 2 mm from the light source, are proposed and evaluated in vivo on Caucasian human skin. The accuracy of the methods was good (2%-7%) for path length and reduced scattering but poor for absorption estimation. Reduced scattering and absorption were systematically lower in the fingertip than in the forearm skin (633 nm). A maximum intrasite and interindividual variation of approximately 35% in an average photon path length was found. The methodology was applied in laser Doppler flowmetry, where path-length normalization of the estimated perfusion removed the optical property dependency.     

An analysis of high efficiency stimulated Raman scattering in water with a frequency-doubled pulsed Nd:YAG source

Abstract

Unexpectedly high stimulated Raman scattering (SRS) has been seen with a frequency-doubled Nd:YAG pump laser (532 nm) in water. The pump beam was propagated, both focused and unfocused, through a 4m long tank. Threshold pump irradiance for SRS was measured to be 2 × 10¹³ Wm^?2 and Stokes transitions were identified at approximately 3230 and 3380 cm^?1. The maximum conversion efficiency to the Stokes frequencies seen was 13% of pump input, for a focused beam, 4% for unfocused. SRS from an unfocused beam was seen to arise from high irradiance filaments caused by self-focusing in the water. The term Raman Interaction Function (RIF) has been defined here as the irradiance of the pump beam integrated over the interaction length (distance over which the pump beam irradiance is above threshold). The RIF model was been designed to describe the relationship between pump laser parameters and the output at the dominant Stokes frequencies.     

The multiple scattering profile in gamma ray Compton studies

The spectrum of 662 keV gamma radiation, multiply scattered by a nickel sample, has been measured directly in a Compton scattering experiment at a scattering angle of 104°. Under these conditions the multiple profile extends well beyond the single and this affords an opportunity to check the Monte Carlo simulation commonly used to correct the single line shapes (Compton profiles). Measurements in reflection and transmission geometries on thin samples produced markedly different multiple profiles which were found to agree with the simulations within the statistical accuracy of the comparison. This provides the first direct validation of the multiple scattering correction procedure in Compton profile analysis.