Optical parametric amplification of femtosecond pulses tunable from the blue to the infrared with microjoule energies

A white-light continuum is used to seed a two-stage optical parametric amplifier pumped by the second harmonic of a regeneratively amplified Ti:sapphire laser system operating at 824 nm. Microjoule energies are achieved in the signal branch, which is tunable from 472 to 785 nm. Near-transform-limited sub-200-fs pulses are attainable over the vast majority of the tuning range.     

CdCl2后处理的Mn掺杂钙钛矿纳米晶光学性能及其白光LED

Mn²⁺离子掺杂全无机钙钛矿(Mn²⁺∶CsPbX₃,X=Cl, Br)纳米晶(NCs)具有宽发射带、长斯托克斯位移和高量子产率等优势,在固态照明、光电探测和成像等领域有广阔应用前景。然而,目前Mn²⁺掺杂的钙钛矿晶体量子产率很难超过70%,如何改善发光效率,同时调控Mn离子发射中心成为构建高质量白光LED的关键。文章通过CdCl₂后处理技术,进行室温下阳离子交换,获得了高效发光的Cd²⁺和Mn²⁺共掺杂的CsPbCl₃纳米晶。Mn的发射波长可以从604 nm连续调控到624 nm,实现稳定的红光发射。Cd离子掺杂改善了Mn-Cl八面体的晶体场环境,使Mn衰减寿命提高到1.32 ms。此外,通过绿色CsPbBr₃纳米晶和蓝-橙双色Mn∶CsPb(ClBr)₃纳米晶构建了高显色指数的暖白光发光二极管(WLED),其流明效率达60 lm/W,显色指数超过85。     

膜式燃气表能力验证方案的设计与评价

正一、概述本次膜式燃气表量值比对的目的是考察区域内授权的计量技术机构承担膜式燃气表检定的综合技术水平,确定检定结果量值的一致程度。实验室1作为主导实验室制定了膜式燃气表能力验证的比对方案,参加比对实验室为本区域内各法定计量技术机构。二、参加比对的单位区域内具有燃气表计量检定     

科技英语翻译中的词义选择和引申

讨论了科技英语翻译中如何正确选择词义和引申词义。选择词义的根据包括6个方面:词的类别、使用场合、搭配习惯、英美两国语言不同的习惯、单复数词义的差别以及缩写词的全称等。词义的引申主要有两种手段:抽象化和具体化。     

车用尿素溶液加注机检定研究与应用

为解决车用尿素溶液加注机检定技术问题,合理合法开展检定,保障消费者和经营企业合法利益,通过了解车用尿素溶液加注机结构、工作原理、计量性能以及车用尿素溶液的物理特性,选择适合开展检定的计量标准装置,确定检定项目、检定方法、数据处理方法。试验确定车用尿素溶液体积膨胀系数、加注机示值误差和付费金额误差。编制车用尿素溶液加注机地方检定规程,并取得实际应用效果。     

Performance limitations of a free-space optical communication satellite network owing to vibrations: heterodyne detection

Free-space optical communication between satellites in a distributed network can permit high data rates of communication between different places on Earth. To establish optical communication between any two satellites requires that the line of sight of their optics be aligned during the entire communication time. Because of the large distance between the satellites and the alignment accuracy required, the pointing from one satellite to another is complicated because of vibrations of the pointing system caused by two fundamental stochastic mechanisms: tracking noise created by the electro-optic tracker and vibrations derived from mechanical components. Vibration of the transmitter beam in the receiver plane causes a decrease in the received optical power. Vibrations of the receiver telescope relative to the received beam decrease the heterodyne mixing efficiency. These two factors increase the bit-error rate of a coherent detection network. We derive simple mathematical models of the network bit-error rate versus the system parameters and the transmitter and receiver vibration statistics. An example of a practical optical heterodyne free-space satellite optical communication network is presented. From this research it is clear that even low-amplitude vibration of the satellite-pointing systems dramatically decreases network performance.     

Imaging through scattering media by the use of an analytical model of perturbation amplitudes in the time domain

A method of generating images through highly scattering media is presented that involves comparing measurements of the time-dependent intensity of transmitted light with an analytical model describing the sensitivity of that intensity on localized changes in optical properties. A least-squares fitting procedure is employed to derive the amplitudes of the measurement perturbations caused by embedded absorbers and scatterers located along a line of sight between the source and detector. Images are presented of a highly scattering, solid plastic phantom with optical properties closely matched to those of human breast tissue at near-infrared wavelengths. The phantom is a 54-mm-thick slab, containing four small cylinders of contrasting scatter and absorption. Results show that embedded absorbers can be distinguished from embedded scatterers, and that the diffusion perturbation amplitude provides inherently greater spatial resolution than the absorption perturbation amplitude.     

Presence of mind: a reaction to Thomas Sheridan's "Further musings on the psychophysics of presence."

An operator's sense of remote presence during teleoperation or use of virtual environment interfaces is analyzed as to what characteristics it should have to qualify it as an explanatory scientific construct. But the implicit goal of designing virtual environment interfaces to maximize presence is itself questioned in a second section in which examples of human-machine interfaces beneficially designed to avoid a strong sense of egocentric presence are cited. In conclusion, it is argued that the design of a teleoperation or virtual environment system should generally focus on the efficient communication of causal interaction. In this view the sense of presence, that is of actually being at the simulated or remote workplace, is an epiphenomena of secondary importance for design.