Phase measuring profilometry based on elliptically pattern grating

The present study proposes a new method for measuring the surface shape of an object using elliptically pattern grating projection. Based on phase measuring profilometry (PMP), elliptically pattern grating is projected on the surface of the object to measure its shape in 3D. The computing formula for solving the phase by the phase-shifting fringe method is derived, and the 3D shape formula for the altitude is reestablished. The error-contrastive analysis of the object's surface shape is re-established based on the proposed method and traditional PMP. The proposed method was shown to have a strong anti-noise ability and able to measure objects under high noise. More accurate measurement results were obtained by computer simulation and experiment to verify the feasibility of the proposed method.     

Forces on the walls and stagnation zones in a hopper filled with granular material

We measure the pressure and the shear forces acting on the walls of an outflowing hopper using Molecular Dynamics simulations. We find very strong fluctuations which for large opening angles follow a power spectrum but have white noise for smaller angles. We also calculate the shape of the stagnation zones that appear during funnel flow and compare it to the experimentally observed ones.     

用条纹图形拼接法测量三维大物体面形

三维物体面形的测量在各个领域中有着广泛的应用，用莫尔法、调制光场分析法测量具有非接触性、高精度、快速的特点，但对于大物体的测量却存在着许多困难，诸如阴影噪声难以消除、条纹对比度低。考虑到图形的相关性，本文提出了一种基于多孔径拼接原理的测量三维大物体面形的方法：条纹图形拼接法，给出了数学模型、计算机模拟结果和实验结果。     

Measurement of ultrashort laser pulses

A proposal for measuring the pulse shape of ultrashort laser pulses is described. The proposed method consists of a Gamo triple intensity-interferometer to measure the triple-correlation function of the light pulses. A subsequent signal processing algorithm is used to reconstruct the true shape of the light pulses out of their triple-correlation function. The suggested method is quite insensitive to noise, as shown by means of computer simulations.     

极低噪声测试系统的方法研究

介绍了可变负载温度法和低温衰减器法。两种方法都应用了所谓的Y因子测量技术。当前S波段致冷放大器的噪声温度已达到小于7K的水平。测量如此低的噪声温度,对于电缆的损失、衰减器和接头以及仪器和传感器的校准,必须给予极大的关注。两种方法噪声温度的测量已经被应用并作了比较,整个测量的估值精确度小于1K。     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

一种解决光刀断线问题的新方法

用光切法测量物体的三维形貌 ,由于其原理简单、速度快、精度高等特点 ,所以得以广泛应用。针对光切法中一直存在的光刀断线问题进行了讨论 ,并提出采用自适应阈值的光刀中心提取法与一维、二维光刀数据修补技术相结合来解决此问题 ,可同时消除噪声的影响。实验证明 :采用此方法可以取得很好的效果。     

Simulations of measurements of fluorescence lifetimes using noise-modulated light

At the Pattern Recognition group at the Delft University of Technology, we are working on new ways to measure fluorescence lifetimes. There are two well-known ways to measure lifetimes; the phase method and the pulse method. In the phase method fluorescent material is stimulated by sinusoidally modulated light. The emitted fluorescent light will have the same modulation frequency, but there will be a phase shift between the excitation and the emission light. Measuring this phase shift will, after some simple calculation, give the lifetime of the fluorescent material. The second method is the pulse method. Short pulses of light are used to excite the material. The emitted light is detected, and from these measurements the decay curve of fluorescent light is determined. In our research we want to use a new method that may allow us to measure a mixture of lifetimes. We want to use excitation light that is modulated by a white noise signal. We are currently building an experimental setup for these measurements. We have been working on numerical and electrical simulations to investigate the properties of noise signals. Some results of these simulations are presented in this paper.     

Theoretics of remote acoustic monitoring of the level and density of fluid contacting media at the interface

We present a method for monitoring the physical parameters of a medium, based on processing of an acoustic signal reflected from the studied medium. The method makes it possible to rapidly and simultaneously measure the level and density of the reflecting medium owing to acoustic sounding with pulses of different shape. We have obtained the analytic dependences relating the controlled parameters to the phase and amplitude spectra components of the reflected acoustic signal.     

Multi-harmonic measurements of line shape under low absorption conditions

We propose a method that employs the ratios of the 2nd and 4th harmonics at the line center to measure line shape under low absorption conditions. To verify this method, the transition of CO₂ at 6,982.0678 cm^?1 is selected to measure line shape by using the proposed method and direct absorption spectroscopy in laboratory conditions. The results from both methods have a high degree of consistency. This satisfactory agreement indicates the validity of the proposed method.     

Signal uncertainty and psychometric functions in profile analysis

Experiment 1 was conducted to compare the effects of signal frequency uncertainty on the detection of a change in spectral shape and on the detection of a tone in wideband noise. Results indicate that for both tasks the uncertainty effect was small, being on average about 3 dB. In a second experiment, psychometric functions were measured for the detection of changes in the spectral shape of multicomponent complexes. Psychometric functions for profile tasks have a 25-dB range and are similar to those measured for the detection of an increment in the level of a single sinusoid. These psychometric functions are different from those found when detecting a signal in noise, which typically have a 10-dB range. Three equations for the shape of the psychometric functions were compared. The difference in the resulting fits was small, thus preventing an unambiguous choice of functional form.     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

Identification of deterministic chaos by an information-theoretic measure of the sensitive dependence on the initial conditions

One of the most difficult problems in the field of non-linear time series analysis is the unequivocal characterization of a measured signal. We present a practicable procedure which allows to decide if a given time series is pure noise, chaotic but distorted by noise, purely chaotic, or a Markov process. Furthermore, the method gives an estimate of the Kolmogorov-Sinai (KS) entropy and the noise level. The procedure is based on a measure of the sensitive dependence on the initial conditions which is called ε-information flow. This measure generalizes the concept of KS entropy and characterizes the underlying dynamics. The ε-information flow is approximated by the calculation of various correlation integrals.     

三维形貌测量的扫描相移法研究

物体三维形貌测量中常用的光切法的主要优点是易于实现扫描测量大型物体表面,缺点是光刀中心位置难以精确确定;相移法的主要优点是可以用较宽的光栅提高测量的灵敏度与准确度,具有测量速度快和较好的抗静态噪声的能力,缺点是当待测范围较大时,采集图像的像差较大,不利于大型物面的测量.将这两种方法有机地结合起来,取长补短,提出了一种扫描相移法.实验结果表明,这个方法不但适用于长形大物面的形貌检测,而且又大大地减少了图像采集系统畸变误差的影响,从而提高了检测准确度.     

Counting statistics of single electron transport in a quantum dot

We have measured the full counting statistics of current fluctuations in a semiconductor quantum dot (QD) by real-time detection of single electron tunneling with a quantum point contact. This method gives direct access to the distribution function of current fluctuations. Suppression of the second moment (related to the shot noise) and the third moment (related to the asymmetry of the distribution) in a tunable semiconductor QD is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels.     

Extracting the structure of highly reflecting fiber Bragg gratings by measuring both the transmission and the reflection spectra

We demonstrate a novel method that enables one to measure the structure of highly reflecting fiber Bragg gratings. The method is based on measuring both the transmission and reflection spectra of the grating and applying an inverse-scattering algorithm. The use of the transmission spectrum significantly reduces the sensitivity of the reconstruction to measurement noise, and therefore it significantly decreases the measurement duration. We experimentally demonstrate our method for reconstructing the structure of an apodized grating with a reflectivity of 99.91%.     

Interferometric optical signal-to-noise ratio measurements of telecom signals with degraded extinction ratio

We measure full interferograms of telecom signals impaired by noise and investigate their applicability to in-band optical signal-to-noise ratio (OSNR) monitoring in practical systems. We experimentally establish that the dependence of overall shape of the interferogram on a signal's extinction ratio (ER) is strong but not unique. As the ER is being degraded the interferogram evolves in two distinct ways depending on the modulation conditions. The resulting ambiguity in the interferogram shape prevents OSNR measurements on completely unknown signals and necessitates a calibration for each modulator condition. With appropriate calibration, we experimentally demonstrate reliable OSNR measurements in the 5 to 25 dB range for 42.8 Gb/s nonreturn-to-zero, return-to-zero, and carrier-suppressed return-to-zero on-off-keyed signals.     

四象限红外光电探测器噪声检测技术研究

分析了红外探测器的噪声组成与形成原因,针对多元探测器的特点,设计了低噪声多路切换开关电路,实现了噪声等效功率NEP的自动化测量,消除了电路中其他器件引入的噪声干扰。实验结果表明,本测量系统不仅具有较低的测量误差(≤2%),并且可以用于其他多元探测器的噪声检测。