Multiwavelength optoacoustic system for noninvasive monitoring of cerebral venous oxygenation: a pilot clinical test in the internal jugular vein

A noninvasive, high-resolution optoacoustic technique is a promising alternative to currently used invasive methods of brain oxygenation monitoring. We present the results of our pilot clinical test of this technique in healthy volunteers. Multiwavelength optoacoustic measurements (with nanosecond optical parametric oscillator as a source of radiation) were performed on the area of the neck overlying the internal jugular vein, a deeply located large vein that drains blood from the brain and from extracranial tissues. Optoacoustic signals induced in venous blood were measured with high resolution and signal-to-noise ratio despite the presence of a thick layer of overlying tissue (up to 10 mm). The characteristic parameters of the signal at different wavelengths correlated well with the spectrum of the effective attenuation coefficient of blood.     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

Formation and growth mechanism of ripple-like AlN nanowires

Single-crystal ripple-like AlN nanowire with tuned diameter was fabricated through direct reaction aluminum with nitrogen by arc discharge method. The nanowires grow along the [0001] direction and have a radial expansion along the [10[`1]0][10\bar{1}0] direction. The periodic variation of the radial expansion toward [10[`1]0][10\bar{1}0] direction produces the ripple-like AlN nanowires. The growth mechanism of the AlN nanowires is discussed by considering the Al adlayer diffusion on the polar (0001) surface.     

液体光击穿阈值的研究

运用声学基础理论,讨论了激光入射到液体中,激光能量与声信号强度间的变化关系.发现激光能量与声信号强度之间存在着对数线形关系.根据液体中光声信号的连续性,得到了一种求取液体光击穿阈值的新方法.     

超快光声光谱技术的进展和前景

回顾了超快光声光谱学的发展过程并介绍了各种测量手段，论述了文章作者建立的飞秒时间分辨的光声光谱系统的工作原理及实验结果，并展望了超快光声光谱学的未来发展方向和应用前景。     

Control of tissue mechanics upon the repetitive-pulse laser heating of cartilage

The viscoelastic properties of laser-irradiated cartilages are studied with optoacoustic methods upon the thermal excitation of mechanical oscillations by repetitive-pulse laser radiation. The effect of laser power, pulse duration, repetition rate, and irradiation time on the shape of the optoacoustic signal is analyzed. It is demonstrated that the optoacoustic response of the cartilage to the repetitive-pulse radiation of a fiber laser depends on the softening of the tissue upon the variation in its shape. Under repetitive-pulse laser irradiation, the optoacoustic response of the cartilage depends on the mechanical characteristics of the biotissue (elastic modulus, hydraulic permeability, and thickness). A simple model that makes it possible to estimate the contribution of the viscoelastic properties to the formation of the optoacoustic response at various laser repetition rates is proposed.     

Shock-wave generation during dry laser cleaning of particles

Generation of shock waves during a dry laser-cleaning process was examined with the probe-beam-deflection technique. Our experimental set-up allows measurement of a density gradient and a time of flight of the generated optoacoustic waves. With analysis of the measured signals we observed supersonic propagation velocities, density profiles matching the shock-wave profile, and reasonable agreement between the shock-wave theory and measured data. Furthermore, we inspected the mechanisms for the generation of these optoacoustic waves. For the clean surface a rapid thermoelastic surface expansion is the main generation mechanism, creating only weak shock waves; however, during the dry laser cleaning the ejected contaminants generate relatively strong shock waves. This difference is easily observed with our experimental set-up, thus enabling the on-line monitoring of the laser-cleaning process. PACS 79.20.Ds; 81.65.Cf; 43.25.+y     

Reconstruction of Optical Energy Deposition for Backward Optoacoustic Imaging

Visualizing optical properties, such as the optical absorption coefficient, helps us to obtain structural information of biological tissues. In this paper, we present an efficient reconstruction algorithm for optical energy deposition in backward optoacoustic imaging. Note that econstruction of optical energy deposition is the first step to imaging the optical absorption coefficient distribution. This algorithm is derived from the optoacoustic wave equations with line focusing, in which the focusing techniques were utilized to reduce the reconstruction problem from three dimensions (3-D) to one dimension (1-D). Simulations and experiments were conducted to verify efficacy of this algorithm. In the simulations, optoacoustic signals were generated based on the solution of the optoacoustic wave equations. In the experiments, a 3-D backward mode optoacoustic imaging system was built. The system consisted of a Nd YAG laser for optical irradiation and an acoustic detection system with a broadband hydrophone. A phantom was used to illustrate validity of the proposed algorithm. The results show that optical energy deposition can be efficiently reconstructed in both simulations and experiments.     

Antiproton confinement in a Penning-Ioffe trap for antihydrogen

Antiprotons (p[over]) remain confined in a Penning trap, in sufficient numbers to form antihydrogen (H[over ) atoms via charge exchange, when the radial field of a quadrupole Ioffe trap is added. This first demonstration with p[over] suggests that quadrupole Ioffe traps can be superimposed upon p[over] and e(+) traps to attempt the capture of H[over] atoms as they form, contrary to conclusions of previous analyses.     

布拉格光栅中微扰光声孤子

研究了布拉格光栅中光波和声波的相互作用. 利用多重尺度方法,将光声耦合方程约化为非线性薛定谔方程,并给出了单光声孤子和双光声孤子近似解析解. 进一步讨论了光声孤子抑制光速的机理和双光声孤子的相互作用性质. 关键词： 布拉格光栅 光声耦合 多重尺度方法 光声孤子     

Measurement of linewidth of two-photon Doppler-free optoacoustic signal and influence of collision broadening

A simple method of measuring linewidths of Doppler-free optoacoustic signals is introduced, and the influence of collision broadening on the linewidth of such optoacoustic signals is analyzed in this paper.     

Nonlinear optoacoustic transformation in the system of dielectric substrate/submicron metal coating/liquid

The optoacoustic method has been shown to be an accurate technique for the measurement of the properties of submicron metal coatings deposited on a dielectric substrate, i.e., mirrors. The method has been previously theoretically described in terms of a linear model of optoacoustic transformation in a system substrate/coating/liquid. The goal of the present work was to determine the limits at which the linear model is still applicable. The modification of the laser induced acoustic signal profiles and transfer functions of optoacoustic transformation versus the laser fluence was studied for two liquids: ethanol and water.     

Doppler-free optoacoustic spectroscopy

The first observation of Doppler-free optoacoustic spectroscopy is reported. As a first example the P (193) line of the 11-0 band of the B←X transition of ¹²⁷I₂ is used. The output of cw single mode dye laser is split into two equal intensity beams chopped at frequencies ω₁ and ω₂. The nonlinear compoment of the optoacoustic signal at the frequency (ω₁ + ω₂) is detected and Doppler-free resolution is obtained. Comparing the Doppler-free optoacoustic and fluorescence spectra of iodine measured under similar conditions, good agreement is found. Since optoacoustic and fluorescence methods complement each other, this opens up new possibilities for weakly or nonfluorescing molecules.     

Optoacoustic detection of nonlinear absorption in glasses

We report what we believe to be the first measurement of two photon absorption in a solid using the optoacoustic effect. A number of different glasses were studied. The dispersion of the optoacoustic signal of holmium oxide doped glass is compared with the corresponding absorption spectrum at twice the frequency of the incident light.     

Spectroscopic,calibration and RET issues for linear laser-induced fluorescence measurements of nitric oxide in high-pressure diffusion flames

Two different strategies are compared for linear laser-induced fluorescence (LIF) measurements of nitric oxide concentration ([NO]) in counter-flow diffusion flames at high pressures via the A-X(0,0) system. Excitation of NO via a rovibronic transition at 226.03 nm is found to be slightly better compared to a previously utilized excitation wavelength of 225.58 nm. An indirect approach based on the computed spectral overlap fraction is verified and applied to calibrate [NO] measurements in counter-flow diffusion flames at high pressures. A five-level model for NO molecular dynamics is presented and utilized to investigate the effects of rotational energy transfer (RET) on linear LIF measurements of [NO] at pressures up to 15 atm. The results indicate that rotational relaxation effects are essentially negligible under high-pressure conditions at low laser fluences, and thus they need not be accounted for when measuring [NO] using linear LIF. The calibration technique is validated by direct comparisons to [NO] measurements made at pressures up to 5 atm via another calibration method, based on doping NO in counter-flow premixed flames at the same pressure. Using this calibration technique, LIF measurements of [NO] are obtained in a series of counter-flow diffusion flames at pressures up to 15 atm. These measurements are found to be in excellent agreement with previously reported measurements of [NO] in similar flames. PACS 07.35.+k; 33.20.Sn; 42.62.Fi     

Noninvasive quantitative measurement of myocardial and whole-body oxygen consumption using MRI: initial results

The purpose of this study was to investigate the feasibility of a noninvasive approach that combines magnetic resonance imaging (MRI) oximetry and flow measurement to obtain the oxygen consumption in the myocardium and in the whole body. Thirteen healthy male volunteers [mean (+/-S.D.) age: 35+/-7 years] underwent this MR study, which included myocardial oxygen consumption (MVO(2)) measurements in 11 subjects and whole-body oxygen consumption (VO(2)) measurements in 8 subjects. In six subjects, both measurements were obtained. Five subjects had repeated MRI measurements of global MVO(2) in order to verify the reproducibility of this approach. The protocol included in vitro blood sample T(2)-%O(2) calibration, coronary sinus (CS) and main pulmonary artery (MPA) T(2) and phase contrast flow measurement and left ventricular (LV) mass calculation. Based on Fick's law, a global measurement of LV MVO(2) and whole-body VO(2) using MRI was feasible. The MVO(2) values were 11+/-3 ml/min per 100 g LV mass. For repeated measurements, differences in MVO(2) of 1 ml/min per 100 g LV mass appear detectable. The whole-body VO(2) values were 3.8+/-0.8 ml/min/kg body weight. MRI techniques that combine CS and MPA T(2), flow and LV mass measurements to quantify MVO(2) and whole-body VO(2) noninvasively in healthy subjects appear feasible, based on their correspondence to previously published work.     

In vivo measurement of normal rat intracellular pyruvate and lactate levels after injection of hyperpolarized [1-(13)C]alanine

Hyperpolarized technology utilizing dynamic nuclear polarization has enabled rapid and high-sensitivity measurements of ¹³C metabolism in vivo. The most commonly used in vivo agent for hyperpolarized ¹³C metabolic imaging thus far has been [1-¹³C]pyruvate. In preclinical studies, not only is its uptake detected, but also its intracellular enzymatic conversion to metabolic products including [1-¹³C]lactate and [1-¹³C]alanine. However, the ratio of ¹³C-lactate/¹³C-pyruvate measured in this data does not accurately reflect cellular values since much of the [1-¹³C]pyruvate is extracellular depending on timing, vascular properties, and extracellular space and monocarboxylate transporter activity. In order to measure the relative levels of intracellular pyruvate and lactate, in this project we hyperpolarized [1-¹³C]alanine and monitored the in vivo conversion to [1-¹³C]pyruvate and then the subsequent conversion to [1-¹³C]lactate. The intracellular lactate-to-pyruvate ratio of normal rat tissue measured with hyperpolarized [1-¹³C]alanine was 4.89±0.61 (mean±S.E.) as opposed to a ratio of 0.41±0.03 when hyperpolarized [1-¹³C]pyruvate was injected.     

Application of the optoacoustic effect in optically pumped submillimeter lasers

The dependence of the optoacoustic signal generated in an optically pumped submillimetre laser system on gas pressure and modulation frequency has been studied experimentally and the results accounted for theoretically. With care an extracavity optoacoustic cell containing the laser gas diluted with air can be used to stablize the pump laser frequency to maximum absorption but this does not always optimise laser output.     

Hole intersubband transitions in GaAs/AlGaAs multiple quantum wells… A new method for determining the Luttinger parameters

Resonant electronic Raman scattering from photoexcited holes has been observed for multiple quantum wells (MQW's) grown in the [111]b and [100] directions. The measurements indicate that the heavy hole mass in the [111] direction is 0.75mo. This value is 2.2 times larger than the value characteristics of the [100] direction. The measurements also quantify the degree of anisotropy for the light holes. We propose a new set of Luttinger parameters that describe the anisotropy of the valence band in GaAs and are consistent with the interband and intersubband transitions observed in [100] and [111]b MQW's.     

Collisionless infrared energy deposition in OCS

We report experiments which show that OCS does not undergo collisionless infrared multiphoton dissociation at high fluences (250 J/cm²) and intensities (3 x 10¹¹ W/cm²), at variance with previously published results at lower fluence and intensity. Under these same conditions optoacoustic measurements, furthermore, show that an average of less than one photon per molecule is absorbed.