Optical fiber hydrogen sensor based on light reflection and a palladium-sliver thin film

Thin alloy films of palladium(Pd) and silver(Ag) are deposited onto glass substrates via the direct current(DC) magnetron technique.The hydrogen sensor probe consists of optical fiber bundle and Pd/Ag optical thin film.when the sensor is exposed to hydrogen,the refractive index of Pd/Ag optical thin layer will diminish and cause attenuation changes of the reflective light.It is observed that the thickness of Pd/Ag alloy layer can affect the hydrogen sensor signal.Under different substrate temperatures,several Pd/Ag samples are coated with different thicknesses of Pd/Ag alloy,and the results of a hydrogen sensor based on reflective light from the Pd/Ag alloy thin film are discussed.

Stray light analysis of an on-axis three-reflection space optical system

Stray light analysis of a three-mirror spatial optical system is presented.The entrance pupil diameter （EPD） of the system is 320 mm,the effective focal length（EFL） is 2809 mm,and the field of view（FOV） is 1°×0.5°.Its walls are coated with extinction paint（the absorption coefficient of which is 97%）.The point source transmittance（PST） of the system is thus reduced by up to two orders of magnitude.Moreover, this technique makes it feasible to block the stray light coming from outside of the FOV by increasing the outer baffle length of the system.Adding an inner baffle to both the primary and the secondary mirrors helps not only to block the stray light coming from outside of the FOV but also to decrease the length of the outer baffle.Simulation results show that the PST values are less than 10^（-10） when the off-axis angle is larger than 9°.The stray light is also suppressed effectively by placing a glare stop at the first imaging plane of Cassegrain telescope.It is surprising that the PST value is 10^（-14） when the off-axis angle is 2°with the placement of glare stop at the first image plane.

Measurement of absolute phase shift on reflection of thin films using white-light spectral interferometry

A novel method to measure the absolute phase shift on reflection of thin film is presented utilizing a white-light interferometer in spectral domain. By applying Fourier transformation to the recorded spectral interference signal, we retrieve the spectral phase function Ф, which is induced by three parts： the path length difference in air L, the effective thickness of slightly dispersive cube beam splitter Teff and the nonlinear phase function due to multi-reflection of the thin film structure. We utilize the fact that the overall optical path difference （OPD） is linearly dependent on the refractive index of the beam splitter to determine both L and Teff. The spectral phase shift on reflection of thin film structure can be obtained by subtracting these two parts from Ф. We show theoretically and experimentally that our new method can provide a simple and fast solution in calculating the absolute spectral phase function of optical thin films, while still maintaining high accuracy.

Infrared Emissivity of La0.8Sr0.2MnO3 with Three Different Structures

La_（0.8）Sr_（0.2）MnO_3 samples with rhombohedral, orthohombic and monoclinic structures were prepared by solid state reaction, sol-gel and co-precipitation methods, respectively. Lattice parameters, grain size, morphology, infrared absorption and emissivity of samples were investigated. The results indicated that the average crystallite size calculated from XRD result and particle size of orthohombic sample were smaller than those of the other two samples, and honeycomb shape grains were observed in orthohombic sample. Due to lower crystal symmetry, Mn-O stretching vibration peaks of the three samples shifted to higher infrared wavenumber. According to the theory of wave optics and Kirchhoff law, bigger rhombohedral sample showed higher emissivity than monoclinic one. However, due to the honeycomb structure of orthohombic sample, repeated reflection and scattering led to the increase of absorption, and orthohombic sample exhibited the highest emissivity.

Accurate Measurement Method for Tube's Endpoints Based on Machine Vision

Tubes are used widely in aerospace vehicles, and their accurate assembly can directly affect the assembling reliability and the quality of products. It is important to measure the processed tube＇s endpoints and then fix any geometric errors correspondingly. However, the traditional tube inspection method is time-consuming and complex operations. Therefore, a new measurement method for a tube＇s endpoints based on machine vision is proposed. First, reflected light on tube＇s surface can be removed by using photometric linearization. Then, based on the optimization model for the tube＇s endpoint measurements and the principle of stereo matching, the global coordinates and the relative distance of the tube＇s endpoint are obtained. To confirm the feasibility, ll tubes are processed to remove the reflected light and then the endpoint＇s positions of tubes are measured. The experiment results show that the measurement repeatability accuracy is 0.167 mm, and the absolute accuracy is 0.328 ram. The measurement takes less than 1 min. The proposed method based on machine vision can measure the tube＇s endpoints without any surface treatment or any tools and can realize on line measurement.

Maceral evolution of lacustrine shale and its effects on the development of organic pores during low mature to high mature stage:A case study from the Qingshankou Formation in northern Songliao Basin,northeast China

Organic matter(OM)hosted pores are crucial for the storage and migration of petroleum in shale reservoirs.Thermal maturity and macerals type are important factors controlling the development of pores therein.In this study,six lacustrine shale samples with different thermal maturities from the first member of the Qingshankou Formation in the Songliao Basin,of which vitrinite reflectance(R_(o))ranging from 0.58% to 1.43%,were selected for a comparative analysis.Scanning electron microscopy(SEM)and reflected light microscopy were combined to investigate the development of organic pores in different macerals during thermal maturation.The results show that alginite and liptodetrinite are the dominant primary macerals,followed by bituminite.Only a few primary organic pores developed in the alginite at the lowest maturity(R_(o)=0.58%).As a result of petroleum generation,oil-prone macerals began to transform to initial-oil solid bitumen at the early oil window(R_(o)=0.73%)and shrinkage cracks were observed.Initial-oil solid bitumen cracked to oil,gas and post-oil bitumen by primary cracking(R_(o)=0.98%).Moreover,solid bitumen(SB)was found to be the dominant OM when R_(o)>0.98%,which indicates that SB is the product of oil-prone macerals transformation.Many secondary bubble pores were observed on SB,which formed by gas release,while devolatilization cracks developed on migrated SB.Additionally,at the late oil window(Ro?1.16%),migrated SB filled the interparticle pore spaces.With further increase in temperature,the liquid oil underwent secondary cracking into pyrobitumen and gas,and spongy pores developed on the pyrobitumen at higher levels of maturity(Ro=1.43%),which formed when pyrobitumen cracked into gas.Vitrinite and inertinite are stable without any visible pores over the range of maturities,verifying their low petroleum generation potential.In addition,it was concluded that clay minerals could have a catalytic effect on the petroleum generation,which may explain why organicclay mixtures had more abundant pores than single OM particles.However,after R_(o)>0.98%,authigenic minerals occupied the organic pore spaces on the organic-clay mixtures,resulting in fewer pores compared to those observed in samples at the early to peak oil window.

The color reflectance of marine-terrigenous deposits in LZ908 borehole in south coastal plain of the Laizhou Bay

Color measuring is characterized by high resolution,high efficiency,and low cost. The application becomes increasingly common for tracing sediment sources and climate variation. Borehole LZ908 in the south coastal plain of the Laizhou Bay in northeast China,was used,of which the top 54 m containing all marine facies was focused,to test the feasibility of colorimetry as a climate indi-cator using visible light reflectance spectra and L＊a＊b＊measurement results. The results show a good correction between lightness and calcium carbonate content in marine-terrigenous deposits;therefore,these deposits can be used as a proxy to study climate changes. Factor-analysis on the first derivative values of the raw visible light reflectance spectra produced three principal factors corresponding to goethite,organic matter,and hematite. Down hole variations in the three fac-tor scores,lightness,calcium carbonate content,and grain size were quite consistent. Moreover,high lightness and low factor scores in goethite,hematite,and organics indicated glacial regression deposits,while low lightness and high factor scores in goethite,hematite,and organics indicated interglacial transgression deposits.

A DUAL-MODALITY OPTICAL BIOPSY APPROACH FOR IN VIVO DETECTION OF PROSTATE CANCER IN RAT MODEL

Ultrasound-guided biopsy procedure for prostate cancer diagnosis,which is the current gold standard,involves quasi-random sampling of prostate tissue without any functional guidance.In this study,we discuss the possibility to augment the detection of prostate cancer using a dual-modality optical approach,which can be coupled with the current needle biopsy setup.Two techniques are light reflectance spectroscopy(LRS)that uses a broadband light source and a CCD array spectrometer,and auto-fluorescence lifetime measurement(AFLM)that uses a custom-designed,time-correlated single photon counting(TCSPC)system.Both LRS and AFLM were employed sequentially in this study to measure cancer tissue along with control tissue on a rat prostate tumor model.At an excitation wavelength of 447 nm,we investigated auto-fluorescence decay curves at the emission wavelengths of 532,562,632 and 684 nm for in vivo and ex vivo AFLM.These results show that auto-fluorescence lifetimes at all measured emission wavelengths differ between control and cancerous tissues with 100% specificity and sensitivity.Moreover,absolute values of hemoglobin derivatives and scattering coe±cient were quantified using in vivo LRS.This part of study also demonstrates that light scattering and absorption are significantly different between the control and cancerous tissue.Overall,the study demonstrates that both LRS and AFLM may provide several intrinsic biomarkers for in vivo detection of prostate cancer.

GaInN light-emitting diodes with omni-directional reflector using nanoporous SnO_2 film

Enhancement of light extraction in a GaInN light-emitting diode （LED） employing an omni-directional reflector （ODR） consisting of GaN, SnO2 nanorod and an Ag layer was presented. The ODR comprises a transparent, quarterwave layer of SnO2 nanorod claded by silver and serves as an ohmic contact to p-type GaN. Transparent SnO2 sols were obtained by sol-gel method from SnCl2·2H2O, and SnO2 thin films were prepared by dip-coating technique. The average size of the spherical SnO2 particles obtained is 200 nm. The refractive index of the nanorod SnO2 film layer is 2.01. The GaInN LEDs with GaN/SnO2/Ag ODR show a lower forward voltage. This was attributed to the enhanced reflectivity of the ODR that employs the nanorod SnO2 film layer. Experimental results show that ODR-LEDs have lower optical losses and higher extraction efficiency as compared to conventional LEDs with Ni/Au contacts and conventional LEDs employing a distributed Bragg reflector （DBR）.

Negative refraction and reflection of Gaussian beam on two-dimensional photonic crystal slab

The refraction and reflection of Gaussian beam on two-dimensional photonic crystal （2DPC） slab are studied by the finite-difference time-domain （FDTD） method. It is shown that 2DPC slab enables negative refraction, which is demystified by the distribution of Poynting vector directions and values inside the 2DPC. A negative Goos-Haenchen shift is also found in the simulation.

Effect of the reflection of underlying surface on sky radiance distribution

Sky radiance might be influenced by the multiple reflectance between the earth＇s albedo surface and the atmosphere. Based on the Lambert＇s law and the radiative transfer equation （RTE）, a model is developed to calculate the additional sky radiance at wavelengths of 0.4-3μm due to the reflectance contribution of the underlying surface. The iterative method is used to calculate sky radiance without the reflectance from underlying surface. The hybrid modified delta-Eddington approximation is used to compute the atmospheric reflection of the radiation from the earth＇s surface. An interaction factor is introduced to deal with the multiple reflectance between the atmosphere and the underlying surface. The sky radiance increment is evaluated for some different albedos of the earth＇s surface. The results show that the sky radiance increment rises rapidly while viewing zenith angle is near to 90°and the larger the albedo of the earth＇s surface is, the more obvious this effect appears.

Wide-band double-pass discrete Raman amplifier with reflection of signals and pumps

A wide-band (1530-1610 nm) and high efficient double-pass discrete Raman amplifier is reported. In this Raman amplifier, by using a one-end gilded fiber as the broadband reflector, signals and multi-pump are both reflected to propagate through the gain fiber for a second time. An increase in net gain of more than 150% has been achieved compared with that in the typical co-pumped Raman amplifier. The advantages of this proposed new configuration have been experimentally studied by comparing with the recently existing Raman amplifier configurations.

Rotating properties of Bragg reflections and spatial lattice solitons in rotating photonic lattices

We demonstrate the rotating properties of Bragg reflections and spatial lattice solitons in rotating photonic lattices by analyzing the linear and nonlinear propagations of light. It reveals that the Bragg reflection of the light waves rotates synchronously with the lattices, leading to the rotation of the Bloch waves during propagations. In the presence of nonlinearity, rotating lattice solitons from different transmission bands can propagate in a relatively stable manner. However, reduced-symmetry solitons at point X2 cannot easily rotate synchronously with the lattice, owing to Coriolis forces. Moreover, additional angular momenta are added to the off-axis propagating solitons.

Reliable and broad-range layer identification of Au-assisted exfoliated large area MoS_(2)and WS_(2)using reflection spectroscopic fingerprints

The emerging Au-assisted exfoliation technique enables the production of a wealth of large-area and high-quality ultrathin two dimensional(2D)crystals.Fast,damage-free,and reliable determination of the layer number of such 2D films can greatly promote layer-dependent physical studies and device applications.Here,an optical method has been developed for simple,high throughput,and accurate determination of the layer number for Au-assisted exfoliated MoS_(2)and WS_(2)films in a broad thickness range.The method is based on quantitative analysis of layer-dependent white light reflection spectra(WLRS),revealing that the intensity of exciton-induced reflection peaks can be used as a clear indicator for identifying the layer number.The simple yet robust method will facilitate fundamental studies on layer-dependent optical,electrical,and thermal properties and device applications of 2D materials.The technique can also be readily combined with photoluminescence(PL)and Raman spectroscopies to study other layer-dependent physical properties of 2D materials.

Enhanced spin Hall effect of reflected light with guided-wave surface plasmon resonance

The photonic spin Hall effect(SHE) has been intensively studied and widely applied, especially in spin photonics.However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance(SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.

Effects of packaging structure on optical performances of phosphor converted light emitting diodes

Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity （ACU） of phosphor converted light emitting diodes （pcLED） are investigated by Monte Carlo ray-tracing simulations. It is found that tilt angles of reflective cup and phosphor surface geometries affect the light extraction efficiency and the ACU distinctly. When the tilt angle varied from 60° to 15°, the light extraction efficiency of LED can achieve the improvements of 13.87%, 18.25% and 14.79% respectively, when the phosphor surface geometry is concave, flat and convex, respectively. It is also found the variety law of phosphor concentrations with the change of tilt angles and phosphor surface geometries to maintain a fixed correlated color temperature （CCT）.

Effects of light intensity on reflective ghost imaging

In this letter, we analyze the effects of light intensity find that the brightness of reflective ghost image can on reflective ghost imaging with thermal source. We be changed by modulating the light intensity of the source and the splitting ratio of the beam splitter. The signal-to-noise ratio will be improved by increa.sing the light intensity of the source. More important, we can obtain the reflective ghost image with high image quality by adopting a low light intensity signal beam and a high light intensity reference beam, which is better than the classical optical imaging, because it can reduce the effects of light on the object.

Calculation on diffraction aperture of cube corner retroreflector

On the basis of optical property of cube corner retroreflector （CCR）, a new perception and calculation approach for diffraction aperture of CCR in two different forms is presented. The relationship between diffraction apertures and incident light with six different combinations of reflection order and incident angle is established. Far-field diffraction patterns of CCR under various incident conditions are also provided.

Determination of human skin optical properties in vivo from reflectance spectroscopic measurements

A novel approach has been proved to quickly and non-invasively determine the optical properties of human skin in vivo. It is based on the diffuse reflectance approximation model and subjected to the well established library of absorption spectra of water and hemoglobin. Under the nonlinear least-square algorithm, fitting the measured spectra in the range of 400--1000 nm to the diffusion approximation model, the reduced scattering coefficient and absorption coefficient of skin tissue can be quickly determined in vivo. The results show that this method is convenient and suitable for the real-time clinical application.

Impact of organic contamination in vacuum on laser-induced damage threshold of TiO_2/SiO_2 dielectric mirrors

The influence of organic contamination in vacuum on the laser-induced damage threshold （LIDT） of coatings is studied. TiO2/SiO2 dielectric mirrors with high reflection at 1064 nm are deposited by the electronbeam evaporation method and their LIDTs are measured in vacuum and atmosphere, respectively. It is found that the contamination in vacuum is easily attracted to optical surfaces because of the low pressure and becomes the source of damage, O2 molecules in vacuum with contamination can accelerate the laser-induced damage by observing LIDT and damage morphologies. LIDTs of mirrors have a little change in vacuum compared with in atmosphere when the organic contamination is wiped off. The results indicate that organic contamination is a significant reason to decrease the LIDT in vacuum.