Physics in Melbourne

I survey highlights of the practice of physics and allied sciences in Melbourne,Australia, from the 1850s, soon after Europeans first settled in the area, to the present. I note recognizable sites of past and current physical-science activity that may be visited, as well as exhibits of historic items of physics apparatus. I trace the role of physics, in the course of a century and a half, in the evolution of a pioneering settlement into a large city embedded in a modern industrial economy.     

Integral Method o Reciprocity in the Spectroscopy of Laser Crystals with Impurity Centers

A new method of determining the stimulated emission cross-section spectra from the absorption cross-section spectra, which we call the integral method of reciprocity, is suggested it does not require knowledge of the structure of the impurity-center electron levels. Based on this method, formulas for calculating the radiation lifetime of impurity centers in crystals have been derived. The effectiveness of the integral method of reciprocity was demonstrated in determining the stimulated emission cross sections and radiation lifetime of an ytterbium ion in the laser crystals Yb³⁺:KYW and Yb³⁺:KGW.     

Low energy properties of identical and strongly correlated particles

Interesting qualitative consequences can arise from the quantum mechanical identity among strongly correlated particles that carry spin. This is demonstrated for properties connected with the low energy excitations in molecular and electronic systems. Spatial permutations among the identical particles are used as the key features. The particular behaviour of rotational tunneling molecules or molecular parts under the influence of dissipation are discussed together with the consequences arising for conversion transitions. The relationship between the thermal shifting of the tunneling line and the conversion rate at low and at elevated temperatures is explicated. The valuable information, that can be extracted from the conversion behaviour after isotopical substitution, is explained in detail. At low temperatures qualitative changes are predicted for the conversion rate by deuteration. Weakly hindered rotors show, also experimentally, drastic isotopic effects. The second part is devoted to finite systems of strongly interacting electrons that appear in semi-conductor nano-structures. The lowest excitation energies are strongly influenced by the interaction. They can be understood and determined starting from the limit of crystallized electrons by introducing localized many particle ‘pocket states’. The energy levels show multiplet structure, in agreement with numerical results. The total electron spin, associated with the low energy excitations, is crucially important for the nonlinear transport properties through quantum dots. It allows for instance to explain the appearance of negative differential conductances.     

CsBr高压X光研究

 采用同步辐射X光源和能散法，对CsBr粉末样品进行高压原位X光衍射实验。由金刚石对顶压砧高压装置（DAC）产生高压，用已知状态方程的Pt粉末作内标，由Pt的衍射数据确定样品压力，最高压力达64.4 GPa。实验结果表明：室温常压下原始CsBr样品是具有简单立方结构的晶体，其晶格常数α＝0.428 5 nm。高压下CsBr的结构有所变化，在51.3~58.4 GPa的压力范围内，(110)线和(211)线发生劈裂，从而形成了四方相。     

北京同步辐射装置3B1B生物光谱实验站

本文介绍北京同步辐射装置（ＢＳＲＦ）３Ｂ１Ｂ光束线、生物光谱实验站和圆二色谱仪的基本情况。报道北京正负电子对撞机（ＢＥＰＣ）同步辐射专用光期间，我们在站测量了１１种手征性生物和药物样品的圆二色（ＣＤ）谱，首次在国内利用同步辐射光获取了Ｄ－苯丙氨酸等样品的ＣＤ谱和Ｄ－及Ｌ－亮氨酸对称的ＣＤ曲线。     

紫外可调谐辐射的波长自动跟踪研究

脉冲染料激光器的可见光波段辐射通过共线倍频和非共线混频实现紫外波段的连续可调谐输出.本文报道了一种闭环跟踪方法;在调谐起始波长处,将取样光束在垂直相位匹配方向分割成等光强的两部分,然后在波长调谐时比较和平衡这两部分光强.对该方法在理论上作了分析并在实验中得到成功的验证.获得的自动跟踪效率大于90%.     

WIDE RANGE DETECTOR USING PARABOLIC CYLINDRICAL MIRROR FOR THz APPLICATIONS

A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities, thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed good agreements with classical antenna theory.     

Optical design of a toroidal grating monochromator based beam line on Indus-1

In this paper, we discuss the detailed optical design of a beam line that is under construction on the synchrotron radiation source, Indus-1. Toroidal mirrors are used as pre-and post- focusing elements and a toroidal grating monochromator as a dispersing element. Using three interchangeable gratings, this monochromator will give, at a moderate resolution, a good throughput on the sample in the wavelength range 40 to 1000 Å. Effect of various parameters and their optimization on the resolution and throughput characteristics have been studied by ray tracing calculations, and presented.     

Spherically symmetric static inhomogeneous cosmological models

Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum) energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third of the combined value of radiation pressure and density.     

激光等离子实验中的低能X射线时间谱解谱方法

利用快速Fourier变换(FFT)算法和反卷积原理对Dante谱议测量波形进行了回推获得了激光等离子体源区低能X射线辐射时间波形。解谱方法采用了W.N.Mcelroy等人提出的SANDⅡ解谱方法并与文献[6]中介绍的限幅迭代和周期性光滑技术相配合计算出了能谱时间关系的16分区结果,给出了1989年6月LF-12强激光装置实验的双束靶、漏靶诊断口,入射口的X射线时间谱以及辐射温度时间关系T_R(i)。