Fabrication of optical devices in poly(dimethylsiloxane) by proton microbeam

Optical diffraction grating and micro Fresnel zone plate type structures were fabricated in relatively thin poly(dimethylsiloxane) (PDMS) layers using proton beam writing technique and the performance of these optical devices was tested. PDMS is a commonly used silicon-based organic polymer, optically clear, generally considered to be inert, non-toxic and biocompatible. PDMS has been used as a resist material for direct-write techniques only in very few cases. In this work, PDMS was used as a resist material; the structures were irradiated directly into the polymer. We were looking for a biocompatible, micropatternable polymer in which the chemical structure changes significantly due to proton beam exposure making the polymer capable of proton beam writing. We demonstrated that the change in the structure of the polymer is so significant that there is no need to perform any development processes. The proton irradiation causes refractive index change in the polymer, so diffraction gratings and other optical devices like Fresnel zone plates can be fabricated in this way. The observed high order diffraction patterns prove the high quality of the created optical devices.     

A new possible method for decreasing the wavelenght of Gyrotron

The weak transverse shear magnetic field is first proposed to decrease the working wavelength of Gyrotron. Using Lie perturbation method, we give the modified wave particle resonant relation in guiding magnetic field with weak transverse shear magnetic field.     

Quantitative measurements of OH concentration fields by two-dimensional laser-induced fluorescence

Received: 7 May 1996/Revised version: 21 October 1996     

Diffraction efficiency and signal-to-noise ratio of multiplexed volume phase holograms recorded in a photographic emulsion

The problems related to noise that arise during recording and reconstruction of holograms used in optical data storage or in massive optical interconnection systems are quite similar and can be analyzed in order to improve the quality of the images that these optical systems provide. In this paper, we will analyze noise in cases in which several coherent object waves are simultaneously stored in a phase recording material in a way that allows us to obtain information about the relationship that exists between the recording material and the number of waves that are being stored. The material used in this study is Agfa Gevaert 8E75 HD holographic film processed with a rehalogenating—type bleach bath without a fixation step. Additionally, we show experimentally that it is possible to holographically store more than 400 waves at the same time (in a coherent fashion) using the same storage geometry, with a signal-to-noise ratio larger than 20 and an average diffraction efficiency of 15%.     

Binary polarization pupil filter: Theoretical analysis and experimental realization with a liquid crystal display

The Jones matrix formalism has been applied to evaluate the response of an optical system when a non-uniform polarizing pupil is introduced. With this formalism we analyze and experimentally demonstrate the properties of a binary polarization pupil filter having two regions with two orthogonal linear polarization orientations. We first study the case when no analyzer is placed behind the pupil filter, and both, the transversal and the axial behavior are described in terms of the intensity and the local state of polarization. Then it is shown how the response of the optical system can be easily changed through the orientation of an analyzer placed behind the pupil. We experimentally verified the theory using a twisted nematic liquid crystal display, which produces two orthogonal linear polarization states for two different addressed voltages.     

Geometry optimised ab inttio calculations on 1,5- and 1,2-dicarba-closo-pentaborane (5)

Geometry optimised ab initio LCAO- MO-SCF calculations for the isomeric carboranes 1,5- and 1,2-dicarba-closo-pentaborane (5) are reported. The optimised geometry of the 1,5-isomer agrees with the experimental geometry and for this isomer greater thermo-dynamic stability is predicted. The framework bonding is due mainly to interactions between the apical atoms and those in the equatorial plane, while within this equatorial plane there is very weak bonding.     

一类非线性非完整系统的Routh方程：从Chetaev条件到Euler条件

对于一类其非线性约束方程可展开为关于广义速度的MacLaurin级数的非完整系统,可以在 完全理想的情况下用Lagrange未定乘数法和d'Alembert原理建立其Routh方程.由此可以得到 结论：Chetaev条件只有在线性非完整系统中才成立并且等价于Vacco条件.引入“Euler条件 ”,可以统一Chetaev条件和Vacco条件,统一d'Alembert原理和Hamilton原理,并解决所有 现存于非线性非完整系统中的问题. 关键词： 非线性非完整系统 Routh方程 Chetaev条件 Vacco条件 Euler条件     

Cavity growth in soft adhesives

The growth process of cavities nucleated at the interface between a rigid surface and a soft adhesive layer has been investigated with a probe method. A tensile stress was applied to the highly confined layer resulting in a negative hydrostatic pressure in the layer. The statistics of appearance and rate of growth of cavities as a function of applied negative stress were monitored with a CCD camera. If large germs of cavities were initially present, most of the cavities became optically visible above a critical level of stress independent of layer thickness. Cavities grew simultaneously and at the same expansion rate as a function of applied stress. In the absence of large germs, cavities became optically visible one after another, reaching a limiting size controlled by the thickness of the layer independently and very rapidly. Although, for each sample, we observed a statistical distribution of critical stress levels where a cavity expanded, the mean cavitation stress depended both on surface topography and more surprisingly on layer thickness. We believe that this new and somewhat surprising result can be interpreted with a model for the growth of small germs in finite size layers (J. Dollhofer, A. Chiche, V. Muralidharan et al., Int. J. Solids Struct. 41, 6111 (2004)). This model is mainly based on the dual notion of an energy activated transition from an unexpanded metastable state to an expanded stable state and to the proportionality of the activation energy with the elastic energy stored in the adhesive layer.     

Statistical modeling of imaging process in active night vision systems with gate-light detection

Characteristics of object images observed through scattering media with an active vision system operating in the mode of spatial selection are estimated using the Monte Carlo method. The effect of optical and geometrical conditions of observation on the contrast in images of reflecting objects is considered. Interpretation is given to the obtained dependences. Received: 11 February 2002 / Revised version: 31 May 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +7-38/2225-9086, E-mail: belov@iao.ru     

Phase transitions in lyotropic nematic gels

In this paper, we discuss the equilibrium phases and collapse transitions of a lyotropic nematic gel immersed in an isotropic solvent. A nematic gel consists of a cross-linked polymer network with rod-like molecules embedded in it. Upon decreasing the quality of the solvent, we find that a lyotropic nematic gel undergoes a discontinuous volume change accompanied by an isotropic-nematic transition. We also present phase diagrams that these systems may exhibit. In particular, we show that coexistence of two isotropic phases, of two nematic phases, or of an isotropic and a nematic phase can occur. Received 15 February 2002 and Received in final form 14 June 2002