Fast,common-path,switchable, achromatic phase-shifter for polarization interferometry

Abstract

A fast switchable phase-shifter using a pair of liquid-crystal devices with a switching angle of 60° is described. This phase-shifter can be placed in the common path traversed by the two orthogonally polarized beams emerging from a polarization interference microscope and used for digital phase measurements over a wide range of wavelengths. It can also be used in a stellar interferometer with orthogonally polarized beams for measurements of fringe visibility with white light.     

Laboratory measurements of the light scattering properties of bentonite clay particles embedded in a cylindrical polymer matrix

The volume scattering function and degree of linear polarization of randomly oriented bentonite clay particles were investigated as a function of scattering angle at 543.5?nm, 594.5?nm and 632.8?nm incident laser wavelengths by using a detector array-incorporated laboratory light scattering setup. Readings were taken in steps of 1° from an angle of 10° to 170° and each detector was separated from the next one by an angle of 10°. A transparent cylindrical polymer matrix made of cycloaliphatic amine-cured thermosetting epoxy resin was used to hold the scattering samples in front of the laser beam. For background correction the measurements were taken in differential mode.     

Bending strength dependence of load‐to‐annual ring direction

The bending strength was studied for load‐to‐grain direction at angle of 90° and load‐to‐annual tree ring direction at angle of 45° of almost 700 years old subfossil elm wood from Sava riverbed. Elm wood is widely used because it is solid and hard regarding its weight. However, due to the Elm Dutch disease and mass drying of elm trees in 1950s, nowadays it is almost impossible to find in natural forest stands of south‐eastern Europe a tree of reproductive age. The value and uniqueness of the studied material lies also in the fact that the subfossil elm wood is even rarer than the recent one, and is highly appreciated for its aesthetic and mechanical qualities. Bending strength has been determined by a three‐point bending test. The mean bending strength value is within the limits for recent elm wood. This investigation has shown that such load‐to‐annual ring direction has almost 20 % higher value for bending strength than for loads applied to the longitudinal‐tangential surface (angle of 0°) and to the longitudinal‐radial surface (angle of 90°). This proves that the ring orientation plays an important role in the measurement of mechanical properties of elm wood and that the measurement of the angle of 45° should always be considered for investigation of bending strength.The coefficient of determination of Weibull functions has been close to value of 1, so it has been concluded that the measured bending strength follows Weibull distribution.     

Influence of beam polarisation in laser bending process

Abstract

In this paper, the influence of beam polarisation in the laser bending process was experimentally studied. Based on the laser beam polarisation, the laser absorption of the metallic specimen could be enhanced by increasing the incident angle. The bending angles are achieved in stainless foil specimens without absorptive coatings, and larger bending angles can be produced by single laser scanning with higher incident angles. Multipass laser bending experiments were also carried out on the same material with graphite coatings. The results show that the bending angle per pass is affected obviously by the beam polarisation at lower laser line energy; and the bending angle per pass increases significantly when the total bending angle is large enough. When using polarised light, the laser beam distortion and laser absorption change induced by the variation of the absorptive coatings and laser incident angle are the two main factors that affect the coupled laser energy. The bending rule is the synthesis effect of the two factors.     

Determination by infrared absorption of the orientation of molecules in monomolecular layers

The mean orientation of molecules constituting Langmuir-Blodgett monomolecular layers was determined by infrared absorption with variable incidence transmission by polarizing the beam in the plane of incidence. The absorption calculation is completely developed for axial anisotropy layers when their thickness is small with respect to the wavelength. The experimental results show that the axis of the aliphatic chains makes an angle of 25±4° with the normal to the substratum for behenic acid layers, whereas this angle is only 8±5° for calcium behenate layers.     

Reflection spectra of uninfiltrated and Ba(NO3)2-infiltrated synthetic opal photonic crystals

The reflection spectra of uninfiltrated and Ba(NO₃)₂-infiltrated synthetic opal crystals have been measured using a halogen lamp with a quasi-continuous near-UV through IR spectrum as the light source. The spectra have been analyzed in a specular geometry at angles of incidence from 5° to 45°. The specular reflection spectra show a prominent maximum whose position depends on the angle of incidence. The infiltration of opal with barium nitrate shifts the maximum to longer wavelengths by 50 to 100 nm, depending on the angle of incidence. This effect has been interpreted in terms of the photonic band gap, which depends on the angle of incidence and the refractive index of the material filling the pores. The experimental data are in reasonable agreement with the peak-reflectance wavelengths calculated using well-known relations for Bragg diffraction.     

A novel multiple reflections technique to calibrate polygons and evaluation of its uncertainty of measurement

In the field of angle metrology, angle gauges and polygons are the material artefact standards. Conventionally, autocollimator along with indexing table, are used for the calibration of angle gauges and polygons. A novel multiple reflections method is devised at NPLI to improve the uncertainty of measurements during calibrations. A polygon under calibration is fixed at the centre of a Moore’s indexing table within eccentricity offset ± 20μm. A reference autocollimator is aligned to one of the face of the polygon. A flat reflector is fixed in the centre of a rotatable table. The rotatable table is arranged to collect the optical beam on to the flat reflector then deflected to same face of the polygon, wherefrom the light beam is received at the autocollimator. Thus the optical beam strikes the same face of the polygon twice. Therefore the resolution of the reference autocollimator is virtually doubled. In this experimental setup, two set of readings are obtained simultaneously. One set of the readings corresponds to conventional method and the second set of the readings belongs to the proposed novel method. The readings of the autocollimator are analysed and the results are discussed in the article. The results thus obtained by conventional method are compared with the results obtained using the proposed method. Using this novel calibration method, the uncertainty of measurement is improved from ± 0.39″ to ± 0.23″.     

Characteristic erosion of silica by oblique argon ion beam bombardment

Following previous work on the angular distribution of ejected particles, features of the oblique argon ion beam bombardment of fused silica were elucidated again but from a different aspect. Detailed observations were made of the erosion topographies of fused silica targets obliquely bombarded with partially neutralized argon ion beam at polar angles of 0°, 22.5°, 45° and 67.5° using scanning electron microscopy. The form of the erosion topography changed systematically from isolated circular etch pits at 0° to isolated crescent etch pits at 22.5° and continuous and homogeneous ripple structures at 45°. Scarcely any erosion pattern was found at 67.5°, except for rare band-like structures. Irrespective of the incidence angle of the beam these structures increased in size with total ion dose but their forms remained unchanged. Essentially the same phenomena were observed in the case of sintered SiO₂-5wt.%P₂O₅ and SiO₂-5wt.%B₂O₃ targets in spite of the fact that their surfaces were initially rougher than that of the fused silica target.     

Optical and electrical properties of obliquely deposited a-GeSe<Subscript>2</Subscript> films

Oblique deposition and exposure to photons of energy greater than the bandgap have a marked effect on the structure and consequently on electrical and optical properties of amorphous chalcogenides. This paper presents a detailed study of photoinduced effect and oblique deposition effect on electrical and optical properties of a-GeSe₂ films deposited at different angles (0°–80°). The indirect-optical bandgap energy (2.18 eV) was found to be independent of angle of incidence. The spectral response of refractive index and extinction coefficient has been determined in the wavelength range of 0.6–1 μm using the transmission spectra. Refractive index decreases with the increase in angle of incidence. The value of refractive index was observed to be 2.28 for 0° and 2.00 for 80° films at 0.646 μm. An increase in bandgap was also observed on exposure to the UV light for ∼120 min. The change in bandgap became more significant with the increase in angle of incidence (∼ 2.3% for 0° and ∼10.6% for 80°). The temperature dependence of conductivity along with time dependence and spectral response of photocurrent has also been investigated.     

Texture evolution of transition-metal nitride thin films by ion beam assisted deposition

TiN, VN and CrN were systematically deposited on silicon substrates using ion beam assisted deposition (IBAD) technique at temperatures and ion (N₂⁺) energy ranging from 300 °C to 500 °C and 100 eV to 650 eV, respectively. The results showed that the texture could be controlled by the ion beam energy, flux, and its incident angle, in conjunction with the deposition temperature. For the 0° angle of ion incidence, fiber textures were formed and could be controlled between (111) and (200) surface plane orientation by adjusting ion flux or ion energy. Three types of in-plane textures were produced, when the ion beam was incident at 45° angle, for which cases ion channeling played an important role in the formation of in-plane texture. Using the strain-energy perturbation method, the stability of texture can be further understood. Among the three in-plane textures, the (200) in-plane texture is strain-energy stable, and the others are not.     

High dynamic range measurement of linear birefringence with an electro-optic modulated circular polariscope

This paper presents a common-path electro-optic modulated circular polariscope capable of performing the sequential measurements of the principal axis and retardance of the linearly birefringent media with high accuracy by means of two phase-locked extractions, and with a high dynamic range obtained by the design of optical configuration and the derivation of an easy algorithm. There exist an absolute error of 0.10° on average in the principal axis measurement of 36 times within the range of 0°–180°, and a relative error of 1.10% in the retardance measurement of a λ/2-wave plate by this method. Consequently, the standard deviations for the principal axis angle and retardance measurements are determined to be 0.0033° and 0.086°, respectively, triple standard deviations to the average values of principal axis angle and retardance are just 0.10% and 0.14% with high repeatability, respectively, and corresponding dynamic ranges of 0°–180°.     

Joining of Cf/SiBCN composite with CuPd-V filler alloy

Two compositions of CuPd-V system filler alloy were designed for joining the Cf/SiBCN composite. Their dynamic wettability on the Cf/SiBCN composite was studied with the sessile drop method. The CuPd-8 V alloy exhibited a contact angle of 57° after holding at 1170℃ for 30 min, whereas for CuPd-13 V alloy,a lower contact angle of 28°can be achieved after heating at 1200 ℃ for 20 min. Sound C_f/SiBCN joints were successfully produced using the latter filler alloy under the brazing condition of(1170-1230)℃for 10 min. The results showed that the active element V strongly diffused to the surface of Cf/SiBCN composite, with the formation of V_2 C/VN reaction layer. The microstructure in the central part of the joint brazed at 1200 ℃ was characterized by the V_2 C/VN particles distributing scatteringly in CuPd matrix. The corresponding joints showed the maximum three-point bend strength of 82.4 MPa at room temperature.When the testing temperature was increased to 600 0 C, the joint strength was even elevated to 108.8 MPa.Furthermore, the joints exhibited the strength of 92.4 MPa and 39.8 MPa at 800 ℃ and 900 ℃, respectively.     

新型滤棒激光测径仪测量角的确定

目的 滤棒成型的不规则性,导致了新型激光测径仪测量滤棒直径时传感器会产生入射角差异, 这就会带来测量误差。如何消除激光测径仪测量误差, 得到与滤棒真实直径最相近的测量值便是关键。方法 使用最优直径估计方法获得了最优的测量组合角度, 然后通过求不同组合角度的平均值进行估计, 以减小入射角差异带来的误差。结果 通过最优直径估计法, 在滤棒15°~165°间选取每间隔45°的4个值的平均值, 作为滤棒的测量估计值, 此值与滤棒真实直径的差值满足测量精度 （±0.01 mm） 要求。有效减小了入射角差异带来的误差, 也是最优的测量角分布数值。结论 最优直径估计法能指导合理选取测量角的分布, 并且能有效减小激光测径仪入射角差异带来的测量误差。     

Polarisation dependent nonlinear interaction of two light beams in LiIO3 crystal

We measured the polarisation of the outgoing light beam of constant intensity induced by a nonlinear interaction with a second light beam of constant linear polarisation and variable intensity, in a thin plate of LiIO₃ crystal. The change in the polarisation of the first beam depends on the direction of polarisation of the second beam and cannot be explained as a thermal phenomenon. We present a theoretical explanation of this effect based on the second-order optical nonlinearity of the LiIO₃ crystal.     

Détermination précise de l'angle d'incidence moyen d'un faisceau lumineux à partir de mesures de flux réfléchis

From photometric measurements, the angle of incidence of a light beam has been measured within a few minutes. The ratio of the reflectances of two different dielectric substrates was theoretically calculated using the Fresnel equation for both parallel and perpendicular polarization. These calculations were performed with the help of a computer and are tabulated for various angles of incidence. From the experimental measurements of the definite ratio, the table indicates the precise value of the angle of incidence under consideration. A discussion concerning the results and the experimental conditions is given in order to underline the accuracy of the method and the range in which it is valid.     

Design and development of a thin film dielectric beam combiner

A multilayer thin film device called a beam combiner for a specific photodissociation experiment was designed and developed. The device when operated at 45° angle of incidence transmits auv laser beam and reflects a visible laser beam at the same time with minimum energy loss. The efficiency of the device was found to be better than 90%.     

Polarization effects in a KGd(WO4)2:Nd crystal

Data are presented that demonstrate that, when a laser beam polarized at 45° to the vertical (horizontal) is passed through plane-parallel plates cut from a Nd-doped (4%) potassium gadolinium tungstate crystal and placed between crossed polarizers, the intensity and polarization of the transmitted light are periodic functions of the angle of incidence of the light. When scanned in two mutually perpendicular directions, the plates exhibit highly anisotropic transmission. The polarization at the intensity minima and maxima at the analyzer output is not orthogonal, in contrast to uniaxial crystals.     

Nanostructured chiral silver thin films: A route to metamaterials at optical frequencies

We present a study of the optical properties of three-armed square nanospirals made of silver and realized as nanostructured thin films with Glancing Angle Deposition. Optical property variations with polarization were investigated using numerical simulations. For each polarisation case, two principal resonances were determined corresponding to excitation of plasmonic modes of nanospirals which resonance's frequency depended on the dimensions of the nanospirals. Calculation of current flows in the nanospirals showed patterns resembling those observed in U-shaped resonators. In particular, a mode with anti-parallel current flow in opposite arms indicates the existence of a magnetic-like resonance in the square nanospirals. We present also generalized spectroscopic ellipsometry measurements obtained on one sample at an incidence angle of 25°, and evidence conversion between polarization states even for light polarized in the plane containing one of the arms. The measurements showed good agreement with the results of calculations for an ideal structure. The differences in the conversion of polarization between measurements and calculations were mainly attributed to the existence of structural non-idealities in the actual sample.     

Circular photogalvanic effect observed in silver-palladium film resistors

The surface circular photogalvanic effect (CPGE) at a laser wavelength of 1064 nm was observed for the first time in silver-palladium resistors fabricated by a thick-film technology. The CPGE response was detected using the electrodes oriented parallel to the radiation incidence plane, for the laser beam obliquely incident onto the sample surface. The coefficient of the pulsed laser radiation power conversion into light-induced emf (with the polarity depending on the sign of the circular polarization) amounted to about 80 mV/MW for film dimensions of 0.02 × 20 × 20 mm and a load resistance of 50 Ω. The maximum absolute value of the conversion coefficient was observed for the angles of light incidence of ±60°.     

空芯光纤硅太阳能电池制备及光捕获研究

本文提出一种空芯光纤结构硅基太阳能电池,并探讨其制备方法和光捕获性能.依据平面电池受光原理和空芯波导的限光机制提出了空芯光纤硅基太阳能电池结构,采用卷曲柔性平面非晶硅薄膜电池制备出圆筒形空芯光纤硅电池.通过对比研究入射光量一定的条件下平面电池和空芯光纤电池的光生电流和电压值,评估空芯光纤电池的光捕获效果.通过测量不同光入射角度和光照强度下空芯光纤电池的光生电流和电压值,揭示光入射角度和光照强度对空芯光纤电池光捕获性能的影响关系.研究表明,空芯光纤硅基电池能将入射光线限制在波导结构内反复吸收和反射,从而在光捕获性能方面较平面电池有所提升(~19.8%).光线入射角度对空芯光纤电池的光捕获性能有较大影响,在30°~50°入射时可以获得较大的光生电压和电流值.在0~100 000 lux的光照强度范围内,光生电压先随光照度增加而增大,而后逐渐趋于恒定值.通过卷曲柔性平面硅电池获得光捕获效率较高的空芯光纤硅电池是可行的,采用结构简单、光线单次入射吸收较低的单节薄膜电池制备空芯光纤电池有望获得更好的光捕获效率提升效果.