Photothermal characterization and stability analysis of polymeric dye lasers

The millisecond heat dissipation of pump energy in polymeric, solid-state dye lasers has been studied with photothermal deflection spectroscopy (PTDS) to determine the contribution of that process to photodegradation of the active material. The samples were solutions of Rhodamine 6G in 2-hydroxyethyl methacrylate copolymerized with various amounts of methyl methacrylate or ethylene glycol dimethylacrylate to change the microstructure properties of the matrix. Values of the thermal diffusivity measured with PTDS were in the range 0.6-1.1 x 10(-3) cm(2) s(-1) for all the compositions studied here. A comparison of these values with previous optical data on lasing efficiency and photostability for the same samples indicates that the macroscopic rate of thermal diffusion is not the key factor that limits the efficiency and stability of these lasers, at least for low pump repetition rates (<1 Hz).     

Highly efficient polymeric dye laser pumped at 1.06 μm

A tunable dye laser using a polyurethane-based active element pumped at 1.06 μm was obtained for the first time. The laser, employing polymethine dye 2696_y, has an energy conversion efficiency of 43% and can be tuned within a Δλ=63 nm wavelength interval.     

Stable doped hybrid sol-gel materials for solid-state dye laser

Laser effects have been obtained with dye-doped hybrid xerogel samples prepared several years ago and stored in different "classical" conditions. Firstly, using the same configuration of the laser cavity as was used 4-5 years ago, we have obtained almost identical laser performances, and slope conversion efficiencies were measured up to 80% and operational lifetimes, with 1-mJ initial output energy and 10-Hz repetition rate of several hundred thousand pulses obtained. Secondly, we have introduced the new pyrromethene 605 dye into a hybrid xerogel matrix and obtained good laser performances similar to the rest of the pyrromethene family.     

Dye photodestruction in a solid-state dye laser with a polymeric gain medium

The process of dye photodestruction in a solid-state dye laser is studied, and implemented is a polymeric gain medium doped with a strongly concentrated dye. The behavior of the conversion efficiency in the polymeric gain medium pumped with different laser-pulse repetition rates and the process of dye photobleaching are analyzed. The contribution of the heating of the host material into the dye molecules' deactivation is discussed. The negative effect of high dye concentration on the dye stability under a high pump repetition rate is reported and analyzed for the first time to my knowledge. A comparison of the present results with recently published data demonstrates the major role of photodestruction, rather than direct thermodestruction, in the dye stability of the solid-state gain medium. The role of additives with low molecular weights in the polymeric matrix, for increasing the stability of the gain material, is discussed.     

Permeability of naphthalene in different types of polymeric food packaging materials

The relative permeabilities of naphthalene through different types of common polymeric food packaging materials were determined by migration studies in a controlled environment. The results illustrate that polyolefins, such as low density polyethylene (LDPE), have a higher relative permeability than other polymers, such as polyethylene terephthalate (PET) or polyvinylchloride co-polymer (PVC). This was explained by the correlation between the permeability of the migrant and the glass transition temperature (Tg) of the different polymers, as well as their polarity.     

抽运光方向对染料激光放大器提取效率的影响

对抽运激光的提取效率是染料激光放大器的重要指标,染料激光放大器的提取效率受到泵浦激光抽运方向的影响.文章从纵向抽运的脉冲染料激光放大器的速率方程推导了抽运光顺向抽运和逆向抽运时放大器提取效率的表达式.采用倍频绿光(532nm)Nd:YAG固体激光器进行了不同方向抽运脉冲染料激光放大器的实验研究.理论计算和实验结果都表明了在纵向抽运的染料激光放大器中,随着放大器级间增益的增加,抽运光提取效率逐渐下降,而且采用逆向抽运方式比采用顺向抽运方式获得的抽运光提取效率要高.     

Fragmentation of brittle materials at high rates of loading

Experiments involving the fragmentation of SiC during both quasistatic and high-rate compressive loading are described. Measured fragment size distributions are considered in terms of current ideas regarding high strain rate damage and microfracture. It is concluded that both crack dynamics and crack nucleation via plastic flow mechanisms may be important elements in the failure process.     

Generalized thermoelastic analysis of layer interface excited by pulsed laser heating

In order to investigate the temperature and stress distribution at the interface of an elastic layer and a rigid foundation under laser thermal shock, a boundary element method is presented. The effective stress and temperature fields are calculated at the interface. The bounded layer absorbs the thermal energy from a repetitively pulsed laser in its surface plane. The pulse duration is of the order of the characteristic time for heat to diffuse across the layer thickness, and thus axial heat conduction cannot be neglected. The generalized thermoelasticity assumption based on the Lord and Shulman model on the temperature and stress distribution at the interface of an elastic layer is considered. Comparison with the classical coupled and uncoupled models are investigated. The effects of the pulse duration and layer thickness on the effective stress and temperature distribution of the layer is studied using the classical theory of thermoelasticity. It is found that for the same maximum surface temperature rise, a shorter pulsed laser induces much stronger effective stress wave front. The layer thickness, on the other hand, has minor effect on the effective stress distribution.     

The electric conductivity of a laser plasma excited at a ceramic surface

The electric conductivity of a laser plasma, excited at the surface of a 22KhS ceramics by a pulsed laser radiation, was studied in the presence of an external electric field oriented perpendicularly to the laser beam direction. Depending on the output laser power density, there are three characteristic regimes: (i) the absence of a laser plasma possessing electric conductivity; (ii) the formation of a conducting plasma in which the current is proportional to the laser power density and to the square of the applied electric field strength; (iii) the formation of a conducting plasma in which the current depends linearly both on the laser power density and on the applied electric field strength.     

Adiabatic flow curves of metallic materials at high strain rates

Dynamic compression tests are carried out on Armco iron, Cr-V-steel, Ni-Cr-Mo-V-steel, an austenitic Ni-Cr-Mo-steel, tantalum, nickel and Ni₃Al and magnesium. The flow curves are analysed to determine the influence of the deformation energy which is tranformed into heat on the flow behaviour and mechancial stability. Not only the material properties but also the conditions of friction between the specimen and the compression tool are found to have a greate influence on the flow stress reduction and stability. High frictional forces promote mechanical instability of materials with low strain hardening and low strain rate sensitivity.     

光学材料和光学薄膜的光热表征(英文)

光热技术用来测量样品的光学和热特性。简要介绍了光热技术及其在光学薄膜测量和钛蓝宝石激光晶体表征中的应用。光热技术可以提供纯光学光谱学所无法提供的、类似光-热能量转换效率之类的信息。光热技术已被用作质量测试和改善现代光学制造的有用工具。     

Anisotropy in granular materials at different scales

This paper is dedicated to the analysis of the local phenomena which give rise to anisotropy in granular materials. This anisotropy can be observed for small strains (“elastic strains”) as well as large irreversible strains (“plastic strains”). Elastic anisotropy appears to be due to the distribution of contacts, the shape of particles and the non-linear local contact law. Anisotropic non-reversible behaviour seems to be related to two kinds of anisotropy, the usual geometric anisotropy and a static anisotropy governing the distribution of contact forces.     

TC11钛合金几种不同横梁位移速率下拉伸试验的K值关系分析

选取Φ5 mm的TC11钛合金圆棒拉伸试样,在3种不同型号的电子拉伸试验机上按照ISO 6892—1:2016中的方法A2选取不同的横梁位移速率进行室温拉伸试验,在试样上装夹引伸计,测量Fp0.2感兴趣点处和弹性阶段的80％Fp0.2处试样上的真实应变速率.通过比较试样平行长度上的名义应变速率与试样不同感兴趣点处的真实...     

聚合物基纳米复合材料的研究进展

对聚合物基纳米复合材料的研究进展进行了介绍,报道了有关聚合物基纳米复合材料制备方法的研究进展情况,并分别对聚合物/粘土纳米复合材料、环氧树脂基纳米复合材料、聚酯纳米复合材料、聚合物/碳纳米管纳米复合材料的研究发展情况给予了评述,同时对每种体系特点和存在的问题进行了论述,最后着重指出纳米复合材料制备方法、应用以及开发新的聚合物基纳米复合体系是今后的主要研究方向.     

Constitutive equations of ageing polymeric materials

In a previous paper, a constitutive equation of relaxation behaviour of time-dependent chemically unstable materials has been developed by employing the irreversible thermodynamics of internal variables and Eyring's absolute reaction theory. In that paper, a theoretical expression for the effect of chemical crosslink density,v, on the relaxation rate has been developed. In this paper the creep behaviour of a network polymer undergoing a scission process has been developed. The temperature effect using the WLF equation on the coupled chemomechanical behaviour has also been incorporated into the equation.