Low-coherence interferometry by intensity correlation

‘Low-coherence interferometry’ is an old technique which has had a wide development recently, and is based on the fact that interference with a path difference much longer that the coherence length gives rise to a ‘channeled spectrum’, which can be detected either by a dispersive spectroscope or by a second interferometer with a variable delay. We have tested an alternative way to detect path differences in this kind of interferometry, by analyzing the output intensity fluctuation correlations by a radiofrequency spectrum analyzer, and Fourier transforming the data. This method is suitable for very long path differences. The experiments have been performed with different lengths of single-mode fibre, in Mach–Zehnder and Fabry–Pérot configurations. Received: 30 March 2000 / Revised version: 17 Juli 2000 / Published online: 20 September 2000     

Scanning LLL x-ray interferometry

A new formalism is presented for the theory of scanning LLL x-ray interferometry, which takes account also of the amount of x-ray absorption and of crystal yawing. It is based on the Takagi approach to the dynamical theory of x-ray diffraction and uses, to a great extent, the formalism of quantum mechanics, in order to reduce the algebraic complexity of the Ewald-von Laue approach. The formalism presented here is an easy-to-handle tool for the study of x-ray propagation in multicrystal systems and for the investigation into deviations of the travelling-fringe period from the spacing of diffracting planes, as it explains how interference features change when moving in paramater space.     

紫外超短脉冲激光辐照固体靶产生硬X射线研究

实验研究了紫外高强度超短脉冲激光(248nm, 440fs, 50mJ)辐照固体靶时产生的硬X-射线(>30 keV)能量连续谱,靶上强度达到1017 W/cm2。P极化光45°照射5mm铜片,实验探测到了能量大于200keV的X射线信号,利用Maxwellian分布拟合能谱得到了的超热电子温度为67keV。     

Highly sensitive, single-shot characterization for pulse widths from 0.4 to 85 ps using electro-optic shearing interferometry

Single-shot characterization using electro-optic shearing interferometry (EOSI) is shown for pulse widths ranging from their transform limit (0.4 ps) to 200x their limit (85 ps). In EOSI, the spectral phase is reconstructed by interfering two spectrally sheared replicas of the pulse under test, where the shear is produced by applying linear temporal-phase modulation. We present a new reconstruction algorithm for accurately characterizing chirped pulses, even if the pulse extends beyond the linear region of the phase modulation. Furthermore, since EOSI does not rely on nonlinear optical processes, it requires only 1 nJ pulse energies for all pulse widths, corresponding to a single-shot sensitivity 1000x higher than previously demonstrated.     

Measurement of trench depth by infrared interferometry

Measurement and control of high-aspect-ratio structures such as dynamic random-access memory trenches is an important step in the manufacture of modern memory devices. We present a novel technique based on infrared interferometry that has been implemented in manufacturing and is capable of measuring sub- 0.25-mum -wide and 10-mum -deep trenches nondestructively and with an accuracy of better than 0.1mum .     

光学频率梳啁啾干涉实现绝对距离测量

本文提出一种基于光学频率梳的啁啾脉冲干涉绝对距离测量的方法.通过一对衍射光栅啁啾参考脉冲,分析参考脉冲和测量脉冲的干涉光谱,得到脉冲的中心频率偏移量,从而解算出被测距离.文中详细分析了脉冲啁啾原理和啁啾脉冲干涉测距原理,以及影响测距范围的因素并给出仿真.搭建了改进的Michelson干涉结构,实验得出测距范围受啁啾参数的影响,并与理论分析吻合;在地下长导轨上,进行大范围测距实验.实验结果表明当,在65 m范围内,测量结果与参考测距仪相比,测距精度为33μm,相对精度达到5.1×10~(-7).此外,根据理论分析,通过实验优化了实验装置的测量不确定度.     

Picosecond x-ray laser interferometry of dense plasmas

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 microm of the target surface. A series of high-quality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.     

On intensity interferometry at high multiplicities

Zeitschrift für Physik C Particles and Fields - We are discussing different aspects of single-and multiparticle spectra produced from a source with very high particle density in phase space....     

Electron correlations observed through intensity interferometry

Intensity interferometry was applied to study electron correlations in doubly ionizing ion-atom collisions. In this method, the probability to find two electrons emitted in the same double ionization event with a certain momentum difference is compared to the corresponding probability for two uncorrelated electrons from two independent events. The ratio of both probabilities, the so-called correlation function, is found to sensitively reveal electron correlation effects, but it is rather insensitive to the collision dynamics.     

Measurement of modal damping by electronic speckle shearing interferometry

A time-average electronic speckle shearing interferometer (ESSI) has been used for modal damping measurement. This is effected by a new fringe enhancement technique. The damping factor of a cantilever measured by using this technique agrees well with the value measured by using the accelerometer method. The study shows that time-average speckle interferometry can be used as a convenient tool for modal damping measurement.     

Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.     

Characterization of the transverse coherence of hard synchrotron radiation by intensity interferometry

The transverse coherence of x rays was measured with an intensity interferometer using a 120-microeV-bandwidth monochromator operating at 14.41 keV. By analyzing the transverse coherence profiles, a vertical source profile of a 25-m long undulator of SPring-8, as well as the coherence degradation by a phase object in the beam path, were quantitatively characterized.     

强流脉冲电子束轰击下回喷靶材速度测量与数值模拟

叙述了用高速摄影技术研究强流脉冲电子束与钽金属靶相互作用后靶材的回喷现象,得出了靶材回喷的速度。并且采用EGS4程序和Euler流体力学方程组分别模拟了电子束在靶内的能量沉积和束靶相互作用的动力学过程。实验表明,钽金属靶在强流脉冲电子束轰击下,回喷靶材的轴向速度大于2.9 mm/μs,而模拟结果表明理想情况下回喷靶材自由面的轴向速度可达9.7 mm/μs。实验和理论计算为阻挡回喷靶材的快门设计提供了必要的参数。     

强流脉冲电子束轰击下回喷靶材速度测量与数值模拟

 叙述了用高速摄影技术研究强流脉冲电子束与钽金属靶相互作用后靶材的回喷现象,得出了靶材回喷的速度。并且采用EGS4程序和Euler流体力学方程组分别模拟了电子束在靶内的能量沉积和束靶相互作用的动力学过程。实验表明,钽金属靶在强流脉冲电子束轰击下,回喷靶材的轴向速度大于2.9 mm/μs,而模拟结果表明理想情况下回喷靶材自由面的轴向速度可达9.7 mm/μs。实验和理论计算为阻挡回喷靶材的快门设计提供了必要的参数。     

Self-referencing measurement of an ultrashort pulse by the standard shear interferometry method

A new method for the self-referencing measurement of the amplitude-phase shape of an ultrashort pulse is proposed. The method uses a two-frequency characteristic of the pulse, which is defined as S(F ₁)S(F ₂), where F is the frequency, S(F) is the complex Fourier spectrum of the pulse, and F ₁ and F ₂ are two independent variables. It is shown that this characteristic can be generated as a two-dimensional polychromatic light wave upon generation of the sum frequency of two crossed spectral decompositions of one and the same pulse, as well as upon space-time Fourier transform of radiation of the noncollinearly generated second harmonic of the pulse. In an orthogonal system of transverse coordinates F ₁ + F ₂ and F ₁ ? F ₂, at any given value of F ₁ + F ₂, the radiation frequency of this wave in the direction of the second coordinate F ₁ ? F ₂ does not change. Therefore, the phase structure of the two-frequency characteristic can be reconstructed by the standard method of lateral shear interferometry in the direction of this coordinate. In the reconstructed two-dimensional phase structure of the two-frequency characteristic, any section by the plane F ₁ = const or F ₂ = const yields the phase structure of the spectrum of the pulse under study. This makes it possible to reconstruct the amplitude-phase shape of the pulse.     

CMOS电路瞬态辐照脉冲宽度效应的实验研究

 在“强光一号”加速器上,对两种CMOS反相器和一种CMOS存储器进行了长脉冲状态和短脉冲状态下的辐照实验,测量了CMOS电路的瞬时辐照效应规律,得到了CMOS电路辐射损伤阈值与脉冲宽度的关系,分析了CMOS电路在不同脉冲宽度下的效应差异。实验结果表明：CMOS电路的辐射损伤阈值随脉冲宽度的增加而降低,在20 ns的脉冲宽度辐照下,CMOS反相器4007和4069的闩锁阈值大约为150 ns脉冲辐照下的2倍,CMOS存储器6264的翻转阈值在20 ns脉冲宽度辐照下为150 ns脉冲宽度辐照下的3倍。     

CMOS电路瞬态辐照脉冲宽度效应的实验研究

在“强光一号”加速器上,对两种CMOS反相器和一种CMOS存储器进行了长脉冲状态和短脉冲状态下的辐照实验,测量了CMOS电路的瞬时辐照效应规律,得到了CMOS电路辐射损伤阈值与脉冲宽度的关系,分析了CMOS电路在不同脉冲宽度下的效应差异。实验结果表明：CMOS电路的辐射损伤阈值随脉冲宽度的增加而降低,在20 ns的脉冲宽度辐照下,CMOS反相器4007和4069的闩锁阈值大约为150 ns脉冲辐照下的2倍,CMOS存储器6264的翻转阈值在20 ns脉冲宽度辐照下为150 ns脉冲宽度辐照下的3倍。     

Measurement of large aspheric surfaces by annular subaperture stitching interferometry

A new method for testing aspheric surfaces by annular subaperture stitching interferometry is introduced.It can test large-aperture and large-relative-aperture aspheric surfaces at high resolution, low cost, and high efficiency without auxiliary null optics. The basic principle of the method is described, the synthetical optimization stitching model and effective algorithm are established based on simultaneous least-square fitting. A hyperboloid with an aperture of 350 mm is tested by this method. The obtained peak-to-valley (PV) and root-mean-square (RMS) values of the surface error after stitching are 0.433λ and 0.052λ (λis 632.8 nm), respectively. The reconstructed surface map is coincide with the entire surface map from null test, and the difference of PV and RMS errors between them are 0.031λ and 0.005λ, respectively.This stitching model provides another quantitive method for testing large aspheric surfaces besides null compensation.     

Characterization of nuclear sources via two-neutron intensity interferometry

The neutron energy spectrum and the two-neutron correlation function have been measured for the E/A=45 MeV Ni + Al reaction in order to assess the space-time characteristics of the neutron emitting source. When comparing the data to a statistical model, the kinetic energy spectra, the integrated correlation function as well as the longitudinal correlation function are reproduced by one single source. However, only the inclusion of a short-lived pre-equilibrium component can account for the stronger correlation exhibited by neutron pairs emitted with high total momentum. The correlation function from events defined as peripheral by constraints on the highest charge of the projectile-like fragment does show a significantly weaker correlation than the minimum bias sample.