Simple time-domain optical method for estimating the depth and concentration of a fluorescent inclusion in a turbid medium

A simple time-domain optical method for estimating the depth and concentration of fluorescent inclusions in turbid media is described. We demonstrate direct depth estimation of a localized fluorescent object from the temporal position of the temporal point-spread function maximum. The depth estimation permits recovery of the fluorophore concentration, both of which are essential quantities for optical molecular imaging studies. Since the maximum is independent of the fluorophore concentration, excitation laser power, detector gain, and other system-dependent factors, this method ensures a robust and efficient approach.     

Depth-of-focus reduction for digital in-line holography of particle fields

Poor axial precision caused, in part, by large depth of focus (tau) has been a vexing problem in extraction of particle position from digital in-line holograms. A simple method is proposed to combat this depth-of-focus difficulty. The method is based on decoupling of size and position information. With d, Delta, and lambda being particle diameter, CCD pixel size, and the wavelength, respectively, our main theoretical result is the reduction of tau from tau - d2/lambda to tau - Delta2/lambda for particles of known size. This result is confirmed in laboratory experiments with holograms of calibrated glass spheres.     

Disabling Photoinduced Electron Transfer in 4,4-Difluoro-8(-4′-hydroxyphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene by Phosphorylation

The synthesis and photophysical characterization of the phosphorylated Bodipy dye 5 are reported and compared to those of its hydroxyphenyl counterpart 1. Conversion of the latter by three methods of phosphorylation yields the strongly fluorescent dye 5 which exhibits similar steady-state spectra like 1 but an approximately five times prolonged fluorescence lifetime tau(Fl). We attribute this distinct change from tau(Fl) = 0.7 ns for 1 to tau(Fl) = 3.7 ns for 5 to the suppression of photoinduced electron transfer in 5. This photochemical reaction was previously held responsible for fluorescence quenching in 1. Fluorescence correlation spectroscopy reveals that 5 can be detected by single-molecule methods and that uncaging of phosphate in 5 is a minor problem.     

Discriminability of bursts of reproducible noise.

The ability of human listeners to discriminate pairs of bursts of reproducible noise was examined. A same-different psychophysical method was used. Bursts in a pair were identical on same trials. On different trials, bursts were identical except for tau ms of independent noise located at either the beginning, middle, or end of the pairs of bursts. As the temporal position of the tau ms of independent noise was moved from the beginning to the end of the bursts of noise, discriminability increased. For each temporal position of the independent noise, discriminability was a function of the ratio of the duration of the independent noise (tau) to the total burst duration.     

玻璃荧光寿命测试系统的原理与设计

介绍了荧光寿命的测量原理,设计了一种利用直接记录法,测量掺杂离子的非共振Stokes荧光寿命的测试系统。根据所测样品的基质材料和掺杂离了的种类,选用相应波段的LD管和半导体探测器,合理调节激发光源的脉冲周期和示波器的工作参数,将别是要注意示波器的输入阻抗的选取。测试结果表明,该系统简易、实用,特别适用于玻璃基质中掺杂离子荧光寿命的在线检测。     

Measurement of the neutron lifetime using a proton trap

We report a new measurement of the neutron decay lifetime by the absolute counting of in-beam neutrons and their decay protons. Protons were confined in a quasi-Penning trap and counted with a silicon detector. The neutron beam fluence was measured by capture in a thin 6LiF foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: tau(n)=(886.8+/-1.2[stat]+/-3.2[syst]) s. The systematic uncertainty is dominated by uncertainties in the mass of the 6LiF deposit and the 6Li(n,t) cross section. This is the most precise measurement of the neutron lifetime to date using an in-beam method.     

MONTE-CARLO CALCULATION ON ACHIEVABLE ACCURACY OF TAU LIFETIME MEASUREMENT BY USING TEC TYPE VERTEX CHAMBER IN e+e－ INTERACTION AT CENTER OF MASS ENERGY √s =40GeV

The most accurate tau lifetime measurement in e⁺e^－ experiments by now is reported by MARK Ⅱ with the value (3.20±0.41±0.35)×10^－13 sec. wherein the second and the third terms are statistical and systematic errors respectively. By using TEC (Time Expansion Chamber) type vertex chamber with position resolution 40μ in r-φ plane at similar experimental condition (∫Ldt=40pb^－1), MONTE-CARLO calculation shows: at center of mass energy √s =40GeV the statistical error of tau lifetime can be decreased to 0.13×10^－13 sec. and the systematic error is in a comparable value.     

双光子激发时间分辨荧光光谱测量技术

建立了一台基于高重复频率扫描相机的双光子激发时间分辨荧光光谱测量系统，能够同时测量样品的荧光光谱和寿命. 该系统的时间分辨率为6.5—200ps，光谱分辨率为1—3nm，能够实现快速数据采集以及可靠和可重复的寿命和光谱测量. 利用标准荧光染料(若丹明6G、香豆素314)及其混合溶液对该系统进行了测试，所得到的荧光光谱分布和寿命值与文献报道一致. 实验结果表明，该系统能有效区分多组分荧光团. 这为鉴别多荧光团或多组分生物组织提供了一种独特的对比方法，可用于多光谱分辨荧光寿命成像和荧光共振能量转移成像等方面. 关键词： 荧光寿命 荧光光谱 双光子激发 高重复频率扫描相机     

Measurement of the Lambda b lifetime in the exclusive decay Lambda b --> J/psi Lambda

We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).     

Measurement of the Lambda0b lifetime in the decay lambda0b--> J/psiLambda0 with the D0 detector

We present measurements of the Lambda(0)(b) lifetime in the exclusive decay channel Lambda(0)(b)--> J/psiLambda(0), with J/psi--> mu(+)mu(-) and Lambda(0)--> ppi(-), the B0 lifetime in the decay B0-->J/psiK(0)(S) with J/psi--> mu(+)mu(-) and K(0)(S)-->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in pp collisions at sqrt[s] = 1.96 TeV. The Lambda(0)(b) lifetime is determined to be tau(Lambda(0)(b)) = 1.22(+0.22)(-0.18)(stat) +/- 0.04(syst) ps, the B0 lifetime tau(B0) = 1.40(+0.11)(-0.10)(stat) +/- 0.03(syst) ps, and the ratio tau(Lambda(0)(b))/tau(B0) = 0.87(+0.17)(-0.14)(stat) +/- 0.03(syst). In contrast with previous measurements using semileptonic decays, this is the first determination of the Lambda(0)(b) lifetime based on a fully reconstructed decay channel.     

Wavelength-Resolved 3-Dimensional Fluorescence Lifetime Imaging

We have developed a compact system for wide-field fluorescence imaging, resolved in three spatial dimensions, lifetime and wavelength, that is based on a gated optical intensifier and an all-solid-state diode pumped Cr:LiSAF oscillator-amplifier system. Exploiting spectral separation, the system has been applied to human teeth, obtaining good lifetime contrast between enamel, dentin and caries. Exploiting spectral separation combined with depth resolution, the study of fluorescent microspheres led to an enhancement in both lifetime contrast and lateral resolution.     

A Feasible Add-On Upgrade on a Commercial Two-Photon FLIM Microscope for Optimal FLIM-FRET Imaging of CFP-YFP Pairs

Fluorescence lifetime imaging microscopy (FLIM) based on time-correlated single photon counting (TCSPC) is a widely used method for fluorescence resonance energy transfer (FRET). Here we report a feasible add-on approach to upgrade a commercial two-photon FLIM microscope into a single-photon FLIM microscope which provides optimal FLIM-FRET imaging of FRET pairs consisting of cyan fluorescent proteins (CFPs) as the donor and yellow fluorescent proteins (YFPs) as the acceptor. The capability of the upgraded system is evaluated and discussed, and the imaging performance of the system is demonstrated using FLIM-FRET experiments with a representative CFP-YFP FRET pair (mCerulean-mCitrine).     

Measurement of the collision time of dense electronic plasma induced by a femtosecond laser in fused silica

Electronic plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in fused silica was investigated by use of pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging were combined to determine electronic collision time tau in the conduction band, and tau was measured to be 1.7 fs at an electron density near 5 x 10(19) cm(-3). The lifetime of the electronic plasma is also measured to be approximately 170 fs by use of the time-resolved shadow imaging technique.     

Relationship between depth of a target in a turbid medium and fluorescence measured by a variable-aperture method

The relationship between the depth of a target in a turbid medium and the fluorescence ratio profile measured by use of illumination and collection apertures with variable diameters and the same optical path is shown. The forward problem was studied by Monte Carlo simulations of the propagation of fluorescent light through a theoretical model of a biologically relevant system for a range of aperture diameters. The curve of the fluorescence ratio as a function of the aperture diameter is characterized by a maximum/minimum point whose position shifts linearly with the depth of the target. Furthermore, the position of the maximum/minimum is observed to be insensitive to variations in the fluorescence efficiency and to the optical properties of the target layer or the entire medium.     

Measurement of the B0s lifetime in the exclusive decay channel B0s-->J/psiphi

Using the exclusive decay B0s-->J/psi(mu+mu-)phi(K+K-), we report the most precise single measurement of the B0s lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B0s lifetime, tau(B0s)=1.444(+0.098)(-0.090)(stat)+/-0.020(sys) ps. We also report a measurement for the lifetime of the B0 meson using the exclusive decay B0-->J/psi(mu+mu-)K*0(892)(K+pi-). We reconstruct 1370 signal candidates, obtaining tau(B0)=1.473(+0.052)(-0.050)(stat)+/-0.023(sys) ps, and the ratio of lifetimes, tau(B0s)/tau(B0)=0.980(+0.076)(-0.071)(stat)+/-0.003(sys).     

平均探测时间:研究单个量子点荧光现象的另一种思路

Due to photoluminescence intermittency of single colloidal quantum dots (QDs), the traditional exponential fluorescence lifetime analysis is not perfect to characterize QDs'' fluorescent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, more details about the emission behavior of QDs were revealed.     

Direct time-domain observation of ultrafast dephasing in adsorbate-substrate vibration under the influence of a hot electron bath: Cs adatoms on Pt(111)

The stretching vibration of Cs adsorbed on Pt(111) is excited coherently by resonant stimulated Raman excitation and its time evolution is probed by fs time-resolved second harmonic generation as a function of pump laser fluence I. As I increases, a fast dephasing component with the lifetime of tau=0.7 ps grows, being superimposed on a slow one with tau=1.9 ps. The fast component is a manifestation of pure dephasing caused by elastic and inelastic scattering of hot electrons at adsorbate.     

Atherosclerotic plaque characterization by spatial and temporal speckle pattern analysis

Improved methods are needed to identify the vulnerable coronary plaques responsible for acute myocardial infraction or sudden cardiac death. We describe a method for characterizing the structure and biomechanical properties of atherosclerotic plaques based on speckle pattern fluctuations. Near-field speckle images were acquired from five human aortic specimens ex vivo. The speckle decorrelation time constant varied significantly for vulnerable aortic plaques (tau=40 ms) versus stable plaques (tau=400 ms) and normal aorta (tau=500 ms) . These initial results indicate that different atherosclerotic plaque types may be distinguished by analysis of temporal and spatial speckle pattern fluctuations.     

单光子调制频谱用于量子点荧光寿命动力学的研究

本文开展了基于单光子调制频谱测量量子点荧光寿命动力学特性的研究.在脉冲激光激发下,对探测到的量子点单光子荧光信号进行频谱分析以获得荧光调制频谱,研究发现特征频谱信号幅值与荧光寿命之间存在确定的非线性对应关系.这种单光子调制频谱方法能有效消除背景噪声和单光子探测器暗计数的影响,用于分析量子点荧光寿命动力学特性时在准确度以及时间分辨率方面都较目前普遍采用的荧光衰减曲线寿命拟合方法呈现出明显优势:当涨落误差为5%时,寿命测量准确度提高了一个数量级;当涨落误差和偏离误差均为5%时,对动力学测量效率以及时间分辨率提高了四倍以上.因此单光子调制频谱可以作为获取量子点在短时间尺度内激发态动力学信息的一种有效技术手段.     

Autofluorescence Lifetime Imaging of Cultivated Cells Using a UV Picosecond Laser Diode

Lifetime images of autofluorescence of cultivated endothelial cells were recorded using a novel picosecond laser diode in the near ultraviolet range (375 nm). In contrast to existing picosecond light sources this wavelength permits efficient excitation of the free and protein bound coenzyme NADH with fluorescence lifetimes of 0.4-0.5 ns and 2.0-2.5 ns, respectively. The effective fluorescence lifetime tau(eff) (depending on both lifetimes) was homogenously distributed over the cells with some shortening in the perinuclear region, possibly close to mitochondria. A slight decrease of tau(eff) was observed after inhibition of the mitochondrial respiratory chain, whereas a slight increase was observed after inhibition of the glycolytic pathway, thus indicating variations of the ratio of free and protein bound NADH. Although present applications are still limited by their low pulse energy (< or = 5 pJ), uv picosecond laser diodes have a large potential in high resolution fluorescence microscopy and fluorescence lifetime endoscopy.