Diffractive Devices Research Articles

Observation of unconventional optical diffraction in α-Fe2O3/Si two-dimensional photonic crystal slab fabricated by sol-gel method

The α-Fe2O3/Si two-dimensional (2D) photonic crystal (PC) with hexagonal honeycomb structure was fabricated by self-assembly and solution-dipping method based on colloidal monolayer template with 780 and 470 nm diameter polystyrene (PS) spheres. Optical diffraction measurement was carried out under wavelengths of 800, 532 and 400 nm. An interesting dispersion phenomenon with a hexagonal diffraction pattern composed of six elliptical spots is observed under specific wavelengths. Both theoretical and experimental calculations reveal that the diffraction can only occur when the incident wavelength is smaller than \(\sqrt{3}/2\) of lattice constant, and both the shape and distribution of these spots can be modified by the PC lattice constant and the incident wavelength. All these results reveal that optical properties of these 2D PC slabs are different from conventional diffractive devices.

Morphology-controlled synthesis of ZnO replicas with photonic structures from butterfly (Papilio paris) wing scales for tunable optical properties

ZnO replicas with photonic structures were fabricated from Papilio paris butterfly wing scales and their tunable optical properties were studied. Through modification of the fabrication method, the reticular porous network structure was successfully replicated from dark black (DB) wing scales. The DB wing scale replicas exhibit a photonic band gap (PBG) in the visible region, which overlaps with the visible emission range of ZnO. Both DB and GB (greenish-blue) wing scale replicas can work as one-dimensional diffraction gratings in optical diffraction experiments, whose spot distances can be tuned by different periodic sizes of butterfly wing structure. Moreover, the ZnO DB wing scale replicas exhibit improved photoluminescence (PL) spectra with reduced visible emission and enhanced UV emission, which can both be attributed to the existence of a PBG produced by the reticular porous network structure in DB wing scales. These results can be very helpful in the research of applications of ZnO materials in UV lasing and optical diffraction devices.

Preparation of Calcium Carbonate Superfine Powder by Calcium Carbide Residue

Calcium carbonate superfine powder with high purity was prepared from calcium carbide residue by a liquid phase process using ammonium chloride as extraction agent and ammonium carbonate agent. The effects of some factors on the reaction were investigated. The calcium carbonate was characterized by X-ray powder diffraction device (XRD) and scanning electron microscopy (SEM). The optimum preparation conditions were determined as follows: the concentration of calcium ion 0.3mol/L, The mass ratio of ammonium citrate and calcium ion 0.1, temperature of carbonization 10°C The product is calcium carbonate of single crystal structure with the diameter of 40-90nm.

Diffraction grating with suppressed zero order fabricated using dielectric forces

An electric-field-assisted method to produce diffractive optical devices is demonstrated. A uniform film of liquid UV curable resin was produced as a drying ring from an organic solvent. Dielectrophoresis forces maintained the stability of the thin film and also imprinted a periodic corrugation deformation of pitch 20 μm on the film surface. Continuous in situ voltage-controlled adjustment of the optical diffraction pattern was carried out simultaneously with UV curing. A fully cured solid phase grating was produced with the particular voltage-selected tailored optical property that the zero transmitted order was suppressed for laser light at 633 nm.

Fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse quasicrystals

We report a numerical method to analyze the fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse (2-D TM) structures. The far-field diffraction patterns of the 2-D TM structures can be obtained by the numerical method, and they have a good agreement with the experimental ones. The analysis shows that the fractal characteristics of far-field diffraction patterns for the 2-D TM structures are determined by the inflation rule, which have potential applications in the design of optical diffraction devices.

Formation of Si nanocrystals in glass by femtosecond laser micromachining

We report on the precipitation of Si nanocrystals inside a borosilicate glass by using an 800 nm, 250 kHz femtosecond laser irradiation, which was confirmed with X-ray diffraction, Raman spectra and transmission electron microscopy analyses. Refractive index profile reveals that the refractive index of the Si nanocrystals precipitated region increased up to 8.7% in comparison with that of the unirradiated area, leading to a large diffraction efficiency of the fabricated dot structure. Furthermore, the third-order optical nonlinearity of the Si nanocrystals precipitated glass is greatly enhanced based on the Z-scan measurement. These results may find applications for the fabrication diffractive optical devices and optical switches.

Tunable light diffractor associated with liquid crystal molecular reorientation from homogeneous alignment to periodic twist deformation in micrometre scale

We have demonstrated the formation of a transmissive tunable light diffractor with a fine grating period using a fringe-field switching (FFS) device. The presented device operates as a superposed amplitude and phase grating. The phase grating is formed by a thin slab of a nematic liquid crystal (LC) film and the amplitude grating is constructed by the electrode pattern of the FFS device. The electrode-position-dependent periodic deformation of the LC director as a function of the applied electric field is analysed and the respective occurrence of phase difference in monochromatic, coherent, linearly polarized He–Ne (632.8 nm) laser light is also calculated using the Jones matrix method at operating voltage. The same calculation results show that the transmitted beam of the present FFS diffractor is right-handed elliptically polarized. The operation characteristics of the thin diffracting device are investigated using a He–Ne laser source and a photodetector which shows a significantly large angular deviation of the diffracted beam owing to the small periodicity of LC deformation.

Understanding the long-term chemical and mechanical integrity of cement in a CCS environment

Portland cement can play a major role in providing cost-effective, long-term zonal isolation for CO2 capture and storage (CCS) used to mitigate climate change. However, achieving zonal isolation with Portland cement under supercritical CO2 environment for the required 1,000 year trapping period may be challenging. Some laboratory researchers report that Portland cement disintegrates when exposed to CO2, leading to potential leakage into the atmosphere or other to underground zones. Other researchers cite Portland cement samples from 30–50 year old CO2 EOR wells where sealing integrity was maintained, even though carbonation was found. In this paper we will discuss reasons likely for this disparity between research lab test results and actual well performance data. Carbonation of Portland cement is a thermodynamically favorable process and therefore difficult to avoid. But the effects can be minimized by various reactive chemical components optimized for the specific thermodynamic conditions. Our research shows partial carbonation of Portland cement is not detrimental unless the mechanical integrity is insufficient to provide effective zonal isolation. For these studies we have developed CO2 treatment test cells capable of producing conditions up to 200 °F and 2,000 psi. In addition, various analytical instruments including x-ray diffraction (XRD), thermo-gravimetric analysis (TGA) and mechanical properties measurement devices have been used for this study. In this paper we will discuss the importance of understanding the percentage of carbonation and depth of CO2 penetration, and how to control these factors by optimizing the cement blend. Interestingly, we found the amount of Portlandite { Ca(OH)2} that forms due to cement hydration and the cement-to-water ratio dictates the depth of penetration as well as percentage carbonation. The implications of this in relation to the long term chemical integrity of the cement sheath under downhole CCS conditions is discussed. This paper also includes the results of recent studies on the changes in mechanical properties of a properly optimized Portland cement blend for a period of up to one year. During this period, measurements were made at different time intervals to examine cement specimen treated with CO2 at 200 °F and 2,000 psi in the presence of water. The results show carbonation without any sign of loss of mechanical or sealing integrity that could lead to zonal isolation failure. Results from a separate set of experiments show the following: (1) Carbonation could be minimized by reducing the Portland cement content by adding Pozzolanic materials and by reducing the permeability and (2) Carbonation could help heal micro-cracks that may be caused by various well operations or ageing. However, such carbonation-induced healing is limited only to a certain width of cracks. In summary of this research, it is recommend that: (1) a high quality primary cement job be performed in adherence to all industry best practices; (2) the cement blend be properly optimized to minimize long-term CO2 corrosion; and (3) the sheath be designed for long-term mechanical integrity. This paper will discuss a comprehensive approach that may be taken to help ensure longer-term effective zonal isolation in new CO2 wells and remedial solutions for old wells and for plugging and abandoning wells.

Determination of the relative thermal conductivity of solid samples by X-ray diffraction device

The thermal conductivity (TC) of metal and rock samples was determined, under ambient conditions, using standard X-ray diffraction equipment in which only the diffractometer sample holder had been modified from the original. As the method is comparative, standard reference materials were used: a copper standard for the analysis of metals and marble for the rock specimens. The marble was analyzed beforehand using a quick thermal conductivity meter QTM. In experimental measurements of TC the mean reproducibility value appears to be about 4% while the accuracy is about 5% for the examined rocks, and better for metals.

Low-voltage element of a field-programmable dynamic diffraction grating

A new element of a field-controlled diffraction grating [Grating Light Valve™ diffractive MOEMS device (GLV)] is described, which differs from known similar elements by the physical principle of operation and its structure; other distinctive features are the lower control voltage, the absence of the hysteresis, and the possibility of operation in the analog mode. Experimental characteristics of the GLV element are presented.

Design and optimization of broadband wide-angle antireflection structures for binary diffractive optics

We propose a class of antireflecting structures that can effectively suppress reflections for binary diffractive optics. In this structure, multiple periodic thin films with gradually varying refractive indices are used to shift all reflected diffraction to the transmitted orders. The structure is optimized to operate over broad bands and wide angles using rigorous coupled-wave analysis and genetic algorithms. We validated the structure numerically using finite-difference time-domain methods. The proposed structure may lead to more efficient diffractive devices for applications in thin-film photovoltaic, waveguide coupler, and holographic optical elements.

Force control and powder dispersibility of spray dried particles for inhalation

This study aims towards a deeper understanding of the correlation between particle morphology, cohesion forces, and aerosol performance of spray dried powders for inhalation. Therefore, forces affecting cohesion and dispersion are considered and some novel contact models are introduced to explain the improved powder dispersibility of corrugated particles. Particles with different degrees of corrugation are prepared by spray drying and characterized. Powder dispersibility is measured by positioning a dry powder inhaler in front of the laser diffraction device. The particle sizes of all powders are in the range of x50 = 2.11 ± 0.15 µm. The ratio of mass specific surface area Sm to volume specific surface area SV rises from 0.54 cm3/g (spherical particles) to 0.83 cm3/g (most corrugation). The fine particle fraction (FPF) rises significantly with increasing corrugation at 24 L/min which can be explained by a distinct difference in powder dispersibility. From theoretical models a reduction in cohesion up to 90% can be estimated for corrugated particles compared to spherical particles. Advantages in powder dispersibility can be expected for particles having a lower density and smaller radius of curvature in the contact zone. Both characteristics are given in case of corrugated particles and can be optimized to a certain degree of corrugation. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:303–316, 2010

Electrically switchable multiple volume hologram recording in polymer-dispersed liquid-crystal films

Multiple Bragg hologram recording was investigated in trimethylolpropane triacrylate based polymer-dispersed liquid-crystal thin films. Ten volume holograms were stored at a single location of less than 0.8 mm2 area with the diffraction efficiencies of 6%–15%, by a simplified method of peristrophic multiplexing, and the formation process of multiple volume holograms was presented. Furthermore, volume hologram capacity was studied both experimentally and theoretically in this film. Based on the maximum of Δn, ∼2×10−2, the theoretical capacity of a location could be improved to 25 Bragg holograms with the relatively high diffraction efficiency of 1%, and the holographic storage density of more than 20 Gbits/in.2 was achieved just by peristrophic multiplexing. Finally, electrically switchability for multiple holograms with a low threshold voltage of ∼3 V/μm was realized, which demonstrates that this material is a potential medium for electrically controlled holographic storage or diffraction device.

Line-defect calibration for line-scanning projection display

A method of line-defect calibration for line-scanning projection display is developed to accomplish acceptable display uniformity. The line scanning display uses a line modulating imaging and scanning device to construct a two-dimensional image. The inherent line-defects in an imaging device and optical lenses are the most fatal performance-degrading factor that should be overcome to reach the basic display uniformity level. Since the human eye recognizes line defects very easily, a method that perfectly removes line defects is required. Most line imaging devices are diffractive optical devices that require a coherent light source. This particular requirement makes the calibration method of sequential single pixel measurement and correction insufficient to take out the line defects distributed on screen due to optical crosstalk. In this report, we present a calibration method using a recursively converging algorithm that successfully transforms the unacceptable line-defected images into a uniform display image.

Texture research of metals and rocks on the KSN-2 neutron diffractometer

From the industrial point of view the research activities of the Laboratory of Neu- tron Diffraction (Faculty of Nuclear Sciences and Physical Engineering CTU Prague) are concentrated to the quantitative texture analysis based on the ODF (orientation distribution function). We have developed the experimental and data treatment procedures for this type research. The texture experiments were carried out on the neutron diffractometer KSN-2 using the TG-1 texture goniometer. This diffraction device offers good intensity with wave- lengths in the range 0.095 to 0.141 nm. Experimental data in form of the pole figures or the inversion pole figures were treated by means of these codes: popLA, TODF-N, MAUD, GSAS. Quantitative texture analysis by means neutron diffraction data were used on the investigation of the many samples of the technically interesting materials. For example, we have determined the texture parameters on the oriented Si steel sheets and rock materials (limestone test samples).

Voltage-programmable liquid optical interface

Recently, there has been intense interest in photonic devices based on microfluidics, including displays1,2 and refractive tunable microlenses and optical beamsteerers3,4,5 that work using the principle of electrowetting6,7. Here, we report a novel approach to optical devices in which static wrinkles are produced at the surface of a thin film of oil as a result of dielectrophoretic forces8,9,10. We have demonstrated this voltage-programmable surface wrinkling effect in periodic devices with pitch lengths of between 20 and 240 µm and with response times of less than 40 µs. By a careful choice of oils, it is possible to optimize either for high-amplitude sinusoidal wrinkles at micrometre-scale pitches or more complex non-sinusoidal profiles with higher Fourier components at longer pitches. This opens up the possibility of developing rapidly responsive voltage-programmable, polarization-insensitive transmission and reflection diffraction devices and arbitrary surface profile optical devices. Voltage-programmable liquid surface profiles with large amplitudes resulting from dielectrophoresis are demonstrated. The oil interface formed can be ultrastable and static, or rapidly switchable, as shown in the case of a modulated diffraction grating. The scheme provides the possibility for responsive and polarization-insensitive transmission and reflection devices, and for optical interfaces with arbitrary surface profiles.

Manipulating spatial qudit states with programmable optical devices

The study of how to generate high-dimensional quantum states (qudits) is justified by the advantages that they can bring for the field of quantum information. However, to have some real practical potential for quantum communication, these states must be also of simple manipulation. Spatial qudits states, which are generated by engineering the transverse momentum of the parametric down-converted photons, have been until now considered of hard manipulation. Nevertheless, we show in this work a simple technique for modifying these states. This technique is based on the use of programmable diffractive optical devices, that can act as spatial light modulators, to define the Hilbert space of these photons instead of pre-fabricated multi-slits.

Nanocomposite hybrid photonic media for remote point sensors

The use of lossless optical media exhibiting reversible optical interactions upon exposure to physical and chemical agents allows for the implementation of remote point photonic sensors. Hybrid nanocomposite media represent a new class of sensor materials. They are produced by flexible chemical synthesis methods and can potentially be tailored by design to implement specific functionalities. These materials combined with externally manipulated optical interfaces lead to an emerging class of diffractive photonic devices offering unique sensing potential and advantageous operational features at low cost. The first case studies on ammonia and methanol detection are discussed.

Effects of phase shift between two photo-alignment substrates on diffraction properties in liquid crystalline grating cells

Diffractive optical devices using low-molar-mass liquid crystals are of great important for realizing numerical optical functions such as optical memory and information systems. In the present study the liquid crystalline gratings have been fabricated using a pair of photo-alignment substrates, and effects of the phase shift between the two photo-alignment substrates on the diffraction properties have been investigated. The liquid crystalline grating has been constructed with variable polarization dependence that can be controlled by the phase shift between the two photo-alignment substrates and twisted angles of the nematic directors. The theoretical considerations were also performed using the elastic continuum theory, Jones calculus, and diffraction theory. A guiding principle that controls the diffraction properties of the liquid crystalline grating cell was successfully presented.

Laser microfabrication of L605 cobalt-chromium cardiovascular stent implants with modulated pulsed Nd:YAG laser

Photonics modulation techniques can be effectively used for the laser microfabrication of biomedical implants to achieve better flexibility and control of the available optical power. These enable the processing and manufacturing of biomedical implants like cardiovascular stents and micro-metallic components with reduced heat affected zone (HAZ) and extremely precise edge cutting. Our investigation deals with the study of acousto-optic modulation of a pulsed Nd:YAG laser beam and further profile cutting of thin cobalt-chromium tubes for cardiovascular stent manufacturing. The acousto-optic modulator used in the investigations is a Bragg diffraction device. During one piercing process, the focused laser power is gradually varied from a low value and reaches the maximum as the beam goes deeper into the material. The optimum value for dwell time during which the laser piercing is occurring is found as 58 ms. A 14-step staircase modulating voltage with a maximum AC component of 900 mV was used, and the laser power was 4.4 W in TEM00 operation. Pulsed Nd:YAG laser modulated using an acousto-optic device in the Bragg regime is capable of cutting extremely complex geometries of stents on L605 tubing. Laser cutting resulted in a kerf width of 22.5±0.5 µm. Precise strut dimensions of 112±15 µm for the subsidiary strut, 140±15 µm for the main strut, and 140±15 µm for the link were also obtained. Scanning electron microscopy (SEM) images of L605 stents illustrate the higher strength Co-Cr alloy L605 with the same ductility, its ability to be translated into thinner struts, and improved deliverability. L605 also exhibits enhanced radio visibility thanks to its tungsten content and exceptional work hardening rate for a uniform expansion with minimal recoil.