Astigmatic bessel laser beams

Abstract

The oblique incidence of a He-Ne laser beam onto a phase-only diffractive optical element (DOE) that simultaneously produces several unimode different-order Bessel beams propagating at various angles with respect to the optical axis is studied theoretically and experimentally. It is shown that, under obliquely incident illumination of a DOE that forms Bessel beams, the resulting astigmatic diffraction pattern can be used to unambiguously identify the direction of the Bessel beam's phase rotation and the order of the Bessel mode.     

True beam smoothing in the fractional fourier transform domain

Abstract

The design of a diffractive optical element (DOE) for true beam smoothing in the fractional Fourier transform domain is described. Based on the Fresnel integrals, the intensity distribution on the output plane is calculated accurately and the discretization error of the spherical phase factor is avoided. The ‘fine design' of the DOE for true beam smoothing is completed with the sampling interval chosen as half of the traditional sampling interval. Simulation results show that the intensity at any point on the output plane fully meets the required demands, not just those sampling points used in the optimization.     

Diffractive optical element used in an external feedback configuration to tune the wavelength of uncoated Fabry-Pérot diode lasers

Abstract

A diffractive optical element (DOE) has been designed, fabricated and used in an external feedback configuration to set the wavelength of operation of uncoated Fabry-Pérot diode lasers. The DOE was designed to replace the conventional elements of an external feedback system, which are a collimating lens and grating in the Littrow configuration. The goal was to simplify use of the external cavity laser by replacing the lens and grating with a single optical element while maintaining the performance that is achieved with a grating and lens. Four DOEs were fabricated with two different focal lengths and two different reflectivities. DOE external cavity lasers were tested for maximum tunable range and stability of the wavelength of operation and compared with an external cavity laser based on a lens and grating in the Littrow configuration. A 40 nm tuning range was achieved with the DOE external cavity laser and this is comparable with the tuning range of the external cavity lasers based on a grating and collimating lens in the Littrow configuration.     

Future perspectives including fuel cells,gas turbines,USC and HGCU the US perspective

Abstract

Both the US Department of Energy (DOE) and EPRI are developing models for the evolution of a secure energy future for the USA. Our general views are very similar. However, there are some differences in approach. DOE is concerned with all energy issues in the US future, including electricity, transportation fuels, and the industrial, commercial, and residential energy sectors; EPRI is concerned specifically with the electricity component, principally in the USA, but, as does DOE, also takes a global view.

Both organizations take what is now known as a ‘Roadmapping’ approach. Roadmapping is an example of a ‘Top Down’ planning method: it involves the specification of a “destination” which the research and development program is aimed towards. In the DOE case, the destination refers to a secure energy future. Typically, Roadmapping is concerned with relatively long time scales. Time scales for different technologies are, of course, very different; in a fast-moving technology such as semiconductors, five to ten years may be a long time. For energy, the equipment is large; planning and construction times are long, and the expected lifetimes of the major components are not less than twenty years, and more typically up to forty years. The time scale that both of our organizations talk about is in the range 20–50 years in the future. The DOE model is called ‘Vision 21.’ The specific destination for Vision 21 is the technical design bases for near-zero emission fossil fueled energy plants. The EPRI model is called the ‘Electricity Technology Roadmap’, and more recently we have ‘A Vision of the Electricity System of 2020.’ An important aspect of the method common to both DOE and EPRI is that the destination is developed by what is called a ‘Stakeholder’ group: this involves not only the researchers and developers, but also the eventual customers for the technology, and the users of the products. This will include members with environmental and societal concerns.

In this paper, we will highlight some of the scenarios that emerge from these models. The first part will concentrate on the Department of Energy program; the latter part on the EPRI view, remembering that we are in close agreement on most aspects.     

Multi-Gaussian Ultrasonic Beam Modeling for Multiple Curved Interfaces—an ABCD Matrix Approach

ABSTRACT

A multi-Gaussian beam model uses a superposition of Gaussian beams to simulate the waves radiated from an ultrasonic transducer. We show that propagation and reflection/transmission laws for Gaussian beams in fluids and elastic solids can be written in the form of A , B , C , D matrices that are analogous to the A, B, C, D scalars used in Gaussian optics. This representation leads to simple expressions for a Gaussian beam even after that beam has been transmitted or reflected at multiple curved interfaces and produces a highly modular multi-Gaussian beam model that is also computationally very efficient. Some examples of the use of this model for both planar and curved interfaces are given.     

Order-of-addition experiments: A review and some new thoughts

Abstract

The study of order-of-addition (OofA) experiments is prevalent in many scientific and industrial areas. The statistical design of experiments (DOE) will considerably improve the efficiency of OofA experiments. Designing and modeling the OofA experiments have increasingly received a great deal of attention. In this article, we review the latest work on the design and model of OofA experiments, and introduce some new thoughts. We believe that this article will motivate fruitful applications in real OofA experiments as well as future developments in the methodology.     

Dedicated spectrometers based on diffractive optics: Design,modelling and evaluation

Abstract

The described design of diffractive optical elements for low cost IR-spectrometers gives a built-in wavelength reference and allows ‘spectral arithmetic’ to be implemented in the optical performance of the DOE. The diffractive element combines the function of the lenses and the grating and eliminates the need for alignment of those components in the standard scanned grating spectrometer design. The element gives out a set of foci, each with one spectral component, which are scanned across a detector, thus relaxing the demands for scan angle control. It can thus be regarded as an alternative solution to a beam splitter and band pass filter instrument. Software tools have been designed to ease the adaptation of the design to different applications. To model the performance of the spectrometers we have implemented a scalar Rayleigh-Sommerfeldt diffraction model. The gold-coated elements are produced by injection moulding using a compact disc (CD) moulding technique and mould inlays mastered by e-beam lithography. The optimized selection of wavelength bands and the classification of the measured signal use a combination of principal component analysis and robust statistical methods. Typical applications will be material characterization of recycled plastics and gas monitoring. Spectrometers for two different applications have been built and tested. Comparisons between the design goals and the measured performance have been made and show good agreements.     

Optimization of gliclazide loaded alginate-gelatin beads employing central composite design

Abstract

Objective: The aim of this study was to optimize the formulation of alginate-gelatin (AL-GL) beads containing gliclazide (GLZ) employing design of experiments (DOE).

Significance: DOE enabled identification of the interaction between the studied factors, deep understanding of GLZ release pattern and acceleration of the optimization process.

Methods: A three-factor, three-level face centered design was employed. The effects of GLZ content (GLZ%, X₁), polymer ratio (AL:GL ratio, X₂), crosslinker concentration (glutaraldehyde, GA%, X₃), and their interaction on incorporation efficiency (IE) and release rate were studied. The optimized formulation was prepared using numerical optimization and evaluated by DSC, FT-IR, SEM and release rate studies.

Results: Increasing GA% (X₃) decreased IE (Y₁) with the highest magnitude of effect among the studied factors. On the other hand, increasing alginate content in AL:GL ratio (X₂) increased IE (Y₁). The amount of GLZ released Q_0.5h, Q_2h(pH 1.2) and Q_4h(pH 7.4) decreased by increasing GLZ% (X₁) and AL:GL ratio (X₂). Both drug content and AL:GL ratio appeared to affect water penetration into the gel matrix and drug release. Generally, there was a direct relationship between GA% (X₃) and GLZ release in pH 1.2 (Q_0.5h and Q_2h). However, in pH 7.4 (Q_4h), increasing GA% decreased GLZ release. In addition, increasing GA% caused deviation from zero-order release model. The actual responses of the optimized formulation were in close agreement with the predicted ones.

Conclusion: The selected factors and their levels studied in the optimization design were useful for tailoring the anticipated formulation characteristics and GLZ release pattern.     

Effect of Strong Pump Depletion on Two-beam Coupling in Photorefractive BaTiO3 at 442 nm

Abstract

Photorefractive BaTiO₃ crystal illuminated at 442 nm gives a large initial scattering level, which leads to strong pump depletion into beam fanning. Studies on the time development of beam fanning show a temporal shift of the fanned beam maximum towards the c-axis direction. The effect on the signal beam amplification of the strong pump depletion into beam fanning has been investigated, revealing different temporal development of the amplified signal for various cross-angles. Our observations on beam fanning in the presence and in the absence of a signal reveal that there is appreciable coupling between the fanned beam and the signal.     

Levelling the focal spot intensity of the focused gaussian beam

Abstract

It is experimentally and numerically shown that a simple binaryphase optical element can be used for levelling the light energy in the focal plane of the focused Gaussian beam, generating a square-shaped focal beam, and transforming the Gaussian beam into a uniform beam which preserves its radius at a definite length of its path.     

Beam propagation factor of decentred gaussian and cosine—gaussian beams

Abstract

On the basis of the second moment method, the beam propagation factor (M ²?factor) of decentred Gaussian beam has been derived, and analysed physically. Then, the result is extended to novel sinusoidal-Gaussian beams, one type of which is the cosine—Gaussian beam, which can be regarded as a superposition of two decentred Gaussian beams.     

Optical Spectroscopy of Inorganic Solids

Abstract

The inhomogeneity of thin films of ZrO₂ and TiO₂ was reduced by ion beam bombardment with mixed argon and oxygen as a working gas during deposition. The inhomogeneities of the films were calculated from transmission monitoring curves. The optimum ion beam voltage and ion beam current density are 900 V and 12 μA cm^?2 for TiO₂ film.     

Rotation of microparticles with Bessel beams generated by diffractive elements

Abstract

We show that imaging a non-diverging Bessel beam by a spherical lens leads to the generation of a diverging Bessel beam. Expressions for the projections of the Umov-Poynting vector for a two-dimensional TE-polarized Bessel beam and a three-dimensional paraxial linearly polarized Bessel beam are derived. A fifth-order Bessel beam is produced using a single optical element-a 16-level phase-only diffractive helical axicon fabricated using electron beam lithography. This beam was successfully used to trap and rotate 5-10 μm diameter yeast particles and polystyrene beads of diameter 5 μm.     

离子束刻蚀工艺误差对DOE器件的影响

针对衍射光学元件(DOE)的离子束刻蚀工艺,结合掩模套刻过程实例,本文提出了刻蚀误差面形分布的概念.在标量衍射的夫琅和费原理上,进行了误差数值模拟分析及讨论.模拟分析和实验数据结果表明,误差的面形分布在DOE器件的衍射焦斑中心会产生一个明显的光强畸变毛刺亮点,严重破坏了靶场照明的均匀性.     

Gaussian beam conversion using an axicon

Abstract

The paper presents a theoretical investigation of laser beam tailoring using a transparent diffracting phase plate. It is shown that a linear axicon is able to transform a Gaussian beam either into a super-Gaussian profile, a ring-shaped profile or a doughnut profile. All these different intensity distributions are easily obtained by only changing the width of the incident Gaussian beam.     

The beamwidth of bessel-modulated gaussian beams

Abstract

Based on the second-order irradiance moment definition, a closed-form expression for the beam width of Bessel-modulated Gaussian beams (QBG beams) is derived, from which the expressions for the waist width, its position, and beam propagation factor (M ² factor) of QBG beams with complex parameter μ are obtained. The dependence of the beam width and waist position on the parameter μ is analysed and illustrated with numerical examples.     

Quantum Noise Reduction by Photodetection with Feedback

Abstract

A simple model is proposed to account for the generation of sub-shot noise light by feedback of the photocurrent. The model is based on a variable beam splitter controlled by the photocurrent from a detector placed after the beam splitter. The zero-feedback transmittivity is not necessarily unity. The field transmitted by the beam splitter shows reduced photon noise when the feedback causes a decreasing transmittivity.     

Induction self-acceleration of a high-current electron beam

Computer modeling using the particle-in-cell method confirmed that self-acceleration by induction of a high-current relativistic electron beam predicted by G. A. Askar’yan [At. énerg. 6, 658 (1959)] may occur when this beam passes through a thick diaphragm containing an aperture. Pis’ma Zh. Tekh. Fiz. 25, 52–56 (July 26, 1999)     

Interference and the lossless lossy beam splitter

Abstract

By directing the input into a particular mode it is possible to obtain as output all of the input light for a beam splitter which is 50% absorbing. This effect is also responsible for nonlinear quantum interference when two photons are incident on the beam splitter.     

Topological phase in a nonparaxial Gaussian beam

An analysis is made of the structure and evolution of the singularities of a nonparaxial Gaussian beam. It is shown that a Gaussian beam may be represented by a family of straight lines lying on the surface of a hyperboloid and that the wavefront of this beam is a function of a point source situated at a point on the z axis with the imaginary coordinate iz ₀. The argument of this complex function is the topological phase of the beam which characterizes the rotation of the wavefront. The singularities of a nonparaxial Gaussian beam are located in the focal plane and are annular edge dislocations. Dislocation processes near the constriction of the Gaussian beam only occur as a result of aperture diffraction. Pis’ma Zh. Tekh. Fiz. 25, 14–20 (November 26, 1999)