Above threshold dissociation in HD+ using frequency chirped laser pulses

We have theoretically studied the dynamics of above threshold dissociation (ATD) in molecular ions HD⁺ using frequency chirped femtosecond laser pulses from numerical solutions of the time-dependent Schrödinger equation by using the three-dimensional time-dependent quantum wave packet method. Energy-dependent distributions of ATD fragments are analyzed by an asymptotic-flow expression in momentum space. Linearly positive and negative frequency chirped laser pulses are adopted. It is found that varying frequency chirped parameters can change branching ratios of the 1sσ _g and 2pσ _u dissociations channels. The concept of a light-induced potential is used to interpret the ATD process. The angular resolved energy distributions of the photofragments are also illustrated.     

Calibration of field inhomogeneities in a time projection chamber with laser rays

We present some results on the use of a set of laser beams to monitor and to measure the systematic displacements of the electron drift trajectories in a Time Projection Chamber of large (0.6 m³) dimensions.     

Sol–gel broadband anti-reflective single-layer silica films with high laser damage threshold

A simple processing of preparing broadband anti-reflective single-layer silica films is presented in this article. By adding polyvinylpyrrolidone (PVP) into reactant mixture, PVP-containing SiO₂ sol was obtained under base catalyzed hydrolysis and condensation of tetraethoxysilane. The spin-coating films and the dip-coating films were deposited on one side and two sides of quartz substrates. The anti-reflection band is 315 nm wide for dip-coating film and 559 nm wide for spin-coating film and the transmittance reached to 99.95 and 95.92% for dip-coating film and spin-coating film, respectively. By a Nd:YAG lasers the laser damage threshold of as-deposited films was measured at 1064 nm wavelength (1 ns pulse). It ranged from 24 to 33 J/cm² with an average of 28.7 J/cm². Compared to SiO₂ sol without PVP, not only was the anti-reflection band broadened but the anti-reflection and laser damage threshold were retained.     

The threshold current density and incubation time to electromigration in gold films

The electromigration in thin gold films was studied by means of direct drift velocity measurements. A threshold in the electromigration drift velocity was found, and its value is inversely proportional to the gold stripe length. Electron-beam-deposited films, in contrast to sputtered ones, also demonstrated the presence of an incubation time for the cathode displacement. The electromigration activation energy was found to be 0.67–0.72 eV and the effective charge -0.3 to -186. In addition, alloyed Au-10 vol.% Mo specimens were examined. These films showed a much slower mass transport from the anode to the cathode—the opposite direction to that of non-alloyed gold films.     

Measurement of the flux-flow velocity in superconducting films by a time of flight method

Flux has been pulsed in on the left side of a superconducting film with a transport current present. The current moves the flux tubes to the right, where their arrival is sensed with a movable pickup coil. The velocity has been defined by the slope of a plot of distance vs. arrival time. Velocities of 1–3 × 10⁵ cm/sec for the first onset and of 0.5–2.7 × 10⁵ cm/sec for the maximum of the flux field have been measured. The total amount of flux decreased approximately linearly with distance traveled.Supported in part by the National Science Foundation and in part by the Cryogenics Center through a grant from the DOD Themis program. Based in part on a thesis (J.K.) submitted to Stevens Institute of Technology in partial fulfillment of the requirements for the Ph.D. degree.     

Direct calculation of the moments of the distribution of photon time of flight in tissue with a finite-element method

Modeling of the full temporal behavior of photons propagating in diffusive materials is computationally costly. Rather than deriving intensity as a function of time to fine sampling, we may consider methods that derive a transform of this function. To derive the Fourier transform involves calculation in the (complex) frequency domain and relates to intensity-modulated experiments. We consider instead the Mellin transform and show that this relates to the moments of the original temporal distribution. A derivation of the Mellin transform given the Fourier transform that permits closed-form derivations of the temporal moments for various simple geometries is presented. For general geometries a finite-element method is presented, and it is demonstrated that the computational cost to produce the nth moment is the same as producing the first n temporal samples of the original function.     

Role of beam interaction time in laser cladding process

Abstract

This paper discusses the microstructure and mechanical properties of a Co based alloy coating, produced by CO2 laser cladding technique, for steam turbine applications. The role of the laser beam interaction time, the so called dwell time, has been investigated. It has been realised that the beam interaction time has a significant effect on the solidification and microstructure development process. The results indicated that the laser cladded zone exhibited a fine microstructure and a higher hardness after a short interaction time compared with a coarse structure and lower hardness after a long interaction time. Since the dilution of the base material into the cladding was significantly low after a short interaction time, the clad could retain a significant amount of strength after a long exposure time, which is a unique feature for the turbine industries.     

一种时域解调激光干涉仪调制信号的方法

针对某低频水平振动校准设备的激光干涉仪,利用NI公司的多功能采集卡,采集激光干涉仪的调制信号及与其同相位的电容式位移传感器的输出信号.根据激光干涉仪调制原理,提出一种时域解调调制信号的方法.根据调制信号条纹的时域特性和它被限幅的实际特点,利用labview软件实现了信号的解调,并将电容位移传感器信号作为参考信号,还原解调后信号的相位,从而得到振动台高精度的振动波形.实验证明,此方法对连续振动信号的解调效果良好,具有较好的重复性和稳定性,精度可达到激光干涉仪发射激光波长的四分之一.     

Direct calculation with a finite-element method of the Laplace transform of the distribution of photon time of flight in tissue

Reconstruction methods for optical tomographic imaging require the development of models of light transport in highly scattering materials. While the simulation of the full temporal response function arising from a short source light pulse is computationally expensive, there are methods to evaluate efficiently certain transforms of the temporal profile. We previously presented methods to obtain directly the Mellin Transform, which is related to the moments of the temporal intensity distribution; We introduce a similar method to calculate directly the Laplace transform. This method provides an addtional, largely independent measurement type that can be combined with the moments to improve image quality in optical tomography, in particular with respect to the simultaneous reconstruction of absorption and scattering distribution.     

Mass and composition matrix-assisted laser desorption ionization time of flight analysis enabling inference of the sequence of most peptides where the protein of origin is known

Mass spectrometers combining matrix-assisted laser-desorption ionization (MALDI) and time-of-flight analysis are among the most widely used in peptide analysis. They excel at accurate mass determinations on complex samples but, compared with tandem instruments, have very limited capacity to determine amino acid sequence through daughter ion analysis. Here we have investigated the sequence information that can be inferred from the masses of peptides in the special circumstance in which the peptides are known to be sub-sequences of known parent sequences. We show how sequence can be inferred from the measured m/z of a peptide (mass analysis) and examine the parameters that influence the level of confidence that can be placed in "inferred sequences". We further describe how specific amino acid modifications can be used with MALDI-TOF analysis to obtain partial composition information and demonstrate that combined mass and composition (MAC) analysis enables the sequences of most peptide ions to be inferred with very high confidence.     

The ablation threshold in amorphous diamondlike carbon films exposed to an ArF excimer laser radiation

An experimental study of the laser-induced ablation threshold in amorphous diamondlike carbon films is reported. The aim is to assess the possibility of using the material as a photoresist in vacuum-ultraviolet laser lithography. Grown on silicon substrates, 10-nm films were irradiated by 20-ns pulses of a 193-nm ArF excimer laser with variable pulse energy per unit area E _p. It is found that the etch rate is very low if E _p < 20 mJ/cm², whereas a single pulse suffices to remove the film completely if E _p=60 mJ/cm². This is attributed to an increase in the thermal ablation component.     

Corona discharge ion mobility spectrometry with orthogonal acceleration time of flight mass spectrometry for monitoring of volatile organic compounds

We demonstrate the application of corona discharge ion mobility spectrometry with orthogonal acceleration time of flight mass spectrometry (CD IMS-oaTOF) for volatile organic compounds (VOCs) monitoring. Two-dimensional (2D) IMS-oaTOF spectra of VOCs were recorded in nearly real time. The corona discharge atmospheric pressure chemical ionization (APCI) source was operated in positive mode in nitrogen and air. The CD ion source generates in air H(3)O(+)(H(2)O)(n) and NO(+). The NO(+) offers additional possibility for selective ionization and for an increase of the sensitivity of monoaromatic compounds. In addition to H(3)O(+)(H(2)O)(n) and NO(+), we have carried out ionization of VOCs using acetone as dopant gas ((CH(3))(2)COH(+)). Sixteen model VOCs (tetrahydrofuran, butanol, n-propanol, iso-propano, acetone, methanol, ethanol, toluene, benzene, amomnia, dioxan, triethylamine, acetonitrile, formaldehyde, m-xylene, 2,2,2-trifluoroethylamine) were tested using these ionization techniques.     

The thermal inertia of materials heated with a laser pulse faster than relaxation time

The nonlocal hyperbolic heat conduction equation is used to describe the thermal inertia of thin metal films (TMF) heated with femtosecond laser pulses. It is shown that for TMF the signatures of thermal inertia are (i) the delay of the heating process and (ii) the strong localization of the thermal energy in TMF.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Real time diagnosis of transient pulse laser with high repetition by radial shearing interferometer

Transient, high repetition pulse laser can be applied to test numerous physical parameters, where in situ, real time measurement and isolation of vibration is highly demanded. Because of its short half-width, high power, high repetition, and even large distortion, the laser presents unique challenges to conventional diagnosing methods. A system based on a novel cyclic radial shearing interferometer is proposed to diagnose the transient, high repetition pulse laser with common path, no reference plane, and high precision. With the spatial-carrier methods, the system needs only one interferogram to reconstruct amplitude and wavefront of the laser. The theories of amplitude and wavefront reconstruction have been validated by computer simulation, and errors less than 1/1000lambda are obtained for both. Comparing with the results of the ZYGO interferometer, an error less than 1/20lambda for both peak-valley and root-mean-square values is gained with good repeatability for the wavefront. The calibration process and real time diagnosis of a high repetition pulse laser are presented then. Finally, the error consideration and system optimization are discussed in detail.     

Determination of the delay time and feedback strength of a semiconductor laser with optical feedback from time series of radiation intensity

A method for estimating the delay time and feedback of a single-mode semiconductor laser from time series of fluctuations of the laser radiation intensity is proposed. The method is based on searching the nearest neighbors of state vectors chosen in time series in a definite way and is resistant to high noise levels. The efficiency of the method is demonstrated by an example of time series of Lang–Kobayashi equations.     

不同浓度硝酸处理的多孔钛及其体外生物活性

多种表面活化改性方法已用于致密钛表面活化改性, 本研究尝试用不同浓度的硝酸溶液处理浆料发泡法制备的多孔钛. 酸处理多孔钛内孔壁上出现了微小尺寸的酸蚀坑, 其微结构随酸浓度的变化而略有不同, 处理后表面磷灰石沉积能力随酸浓度变化差异显著, 其中以1:1和1:5两种浓度(体积比)的硝酸处理组最强, 并显著促进MG63细胞增殖, 细胞在样品表面和孔内得到良好粘附和铺展. 本研究结果表明硝酸处理活化多孔钛, 方法简单, 不引入杂质, 渗透性好, 可有效活化多孔钛内外表面, 是一种有效的制备生物活性多孔钛的方法.     

Beam-profile modulation of thulium laser radiation applied with multimode fibers and its effect on the threshold fluence to vaporize water

The threshold fluences at which vaporization is initiated at the tip of a multimode fiber that is submerged in water were investigated when free-running and Q-switched thulium laser pulses (lambda = 2.01 mum) were applied with different pulse energies. We focused on the quantification of temporal and spatial fluence modulations of the beam profile at the tip of a 400-mum fiber. The spatial and the temporal fluence peaks over the average fluence were measured to as high as 1.5 and 4 in the Q-switched mode, respectively, and 2.5 and 40 in the free-running mode, respectively. The fluence peaks significantly influence the vaporization process. An increase in the threshold fluence with increasing pulse energy was found for the Q-switched mode, but there was a decrease for the free-running mode. Pressure transients of the order of 1 kbar and temperatures higher than 200 degrees C were calculated for a 30-mJ Q-switched laser pulse at the onset of vaporization. Collecting all the data allowed us to trace the thermodynamic path of rapid heating and vaporization in a phase diagram of water.     

Determination of optimal exposure time for imaging of blood flow changes with laser speckle contrast imaging

Laser speckle contrast imaging is becoming an established method for full-field imaging of cerebral blood flow dynamics in animal models. The sensitivity and noise in the measurement of blood flow changes depend on the camera exposure time. The relation among sensitivity, noise, and camera exposure time was investigated experimentally by imaging the speckle contrast changes in the brain after electrical forepaw stimulation in rats. The sensitivity to relative changes in speckle contrast was found to increase at longer exposure times and to reach a plateau for exposure times greater than approximately 2 ms. However, the speckle contrast noise also increases with exposure time and thus the contrast-to-noise ratio was found to peak at an exposure time of approximately 5 ms. Our results suggests that approximately 5 ms is an optimal exposure time for imaging of stimulus-induced changes in cerebral blood flow in rodents.     

Bayesian prediction in threshold autoregressive models with exponential white noise

In this paper, we develop a Bayesian analysis of a threshold autoregressive model with exponential noise. An approximate Bayes methodology, which is introduced here, and the Gibbs sampler are used to compute marginal posterior densities for the parameters of the model, including the threshold parameter, and to compute one-step-ahead predictive density functions. The proposed methodogy is illustrated with a simulation study and a real example.     

High voltage generator for the power supply of photomultipliers in the time of flight system of Alpha Magnetic Spectrometer-2 experiment

In this report, the behaviour of the first prototype high voltage generator (HVG) that might be used in the time of flight (TOF) system for the AMS-2 experiment is described. The system receives a positive continuous voltage about 100–120 V as input, and it provides a programmable negative continuous voltage from −1600 to −2400 V as output, versus a total load of 50 MΩ. The most important aspect is the absence of a transformer which usually is used in the step-up DC–DC converters. In the TOF system of alpha magnetic spectrometer (AMS)-2 experiment there is a big magnetic field, higher than 2 kG, that does not allow to use a transformer, therefore this prompted us to use the Cockroft–Walton system. The power consumption is about 300 mW and the peak-to-peak high frequency ripple is lower than 0.3% of the output high voltage. We also estimated the reliability of the HVG and we obtained a failure probability lower than 0.5% after three years of continuous functioning. Besides, in this report, much importance was given to the calculation of a simple model of the system to estimate the stability margins.