PPV衍生物／C60薄膜的时间分辨荧光光谱研究

用皮秒锁模Ｎｄ：ＹＡＧ激光器的倍频输出作为激发光，用同步扫描条纹相机系统对聚对苯乙炔ＰＰＶ的两种衍生物，Ｐｏｌｙ（２－ｍｅｔｈｏｘｙ－５－（４－ｂｕｔｅｎｙｌｏｘｙ）ｐｈｅｎｙｌｅｎｅ ｖｉｎｙｌｅｎｅ）（ＭＢＰＰＶ）和Ｐｏｌｙ（２－ｍｅｔｈｏｘｙ－５－（４－ｂｒｏｍｏ－ｂｕｏｘｙ）ｐｈｅｎｙｌｅｎｅ ｖｉｎｙｌｅｎｅ）ＭＢＢ－ＰＰＶ），与富勒烯Ｃ６０的组合薄膜进行时间分辨荧光测量。     

Time resolved photoluminescence near the “band gap” in amorphous silicon

Two broad luminescence bands in weakly hydrogenated (glow discharge) undoped amorphous silicon have been observed using time resolved spectroscopy on a nanosecond timescale. Whereas the luminescence decay of the low energy band has been found to be sample independent, the peak position of the luminescence does show a sample dependence. We propose an intrinsic origin of this luminescence.     

Time resolved photoluminescence spectra of a-As2S3

Time resolved photoluminescence (PL) spectra of a-As₂S₃ are reported in the range 0–100 nsec after the excitation light pulse. After a very careful correction for apparatus spectral response, there is no large shift of the PL line as previously reported, but only an increase of the high energy side of the PL spectrum at short times. These results are discussed in terms of models with or without rearranged point defects.     

High density photoluminescence induced by laser pulse excitation in InSe under pressure

Abstract

We report on high density photoluminescence (HDPL) measurements in undoped indium selenide under pressure at 300 K. Direct electron-hole plasma (DEHP) stimulated emission, induced by high density excitation, has been observed in InSe from room pressure up to 5.1 GPa. Spontaneous and stimulated emission bands observed in the spectra have been analyzed within the framework of the band gap renormalization theory (BGR) in a multi-valley scenario. The pressure coefficients of the spontaneous and stimulated emission bands have led us to attribute these bands to transitions from different minima in the conduction band, which show different renormalization energies determined by the effective masses and electron densities in each valley. Under high excitation, the direct to indirect crossover is shown to occur at a lower pressure than that observed in absorption measurements, as a result of the different renormalization energies of each transition.     

Time resolved Fano resonances

Recent advances in the generation of sub-fs extreme ultraviolet pulses and attosecond metrology have opened up the possibility to trace the time evolution of electronic wave packets inside atoms in pump-probe experiments. We investigate the feasibility of observing the buildup of a Fano resonance in the time domain by attosecond streaking techniques. A time-resolved resonance is initialized by a sub-fs extreme ultraviolet-pump pulse in the presence of a synchronized phase-controlled probe laser pulse. The time evolution of the coherent superposition of resonant state and continuum is mapped onto a modulation of the electron spectrum as a function of the time delay between pump and probe pulse. (super-)Coster-Kronig transitions with lifetimes of approximately 400 asec( are identified as prime candidates.     

Time resolved particle image velocimetry

The temporal evolution of the velocity field of an unsteady fluid flow can be tracked by combining Particle Image Velocimetry (PIV) and high speed photography. Two alternative techniques for PIV are discussed: the classical light sheet technique and a method which makes use of the light scattered in forward direction. We applied time resolved PIV to investigate the flow around cavitation bubbles during their collapse near a solid boundary. The light source was an argon laser with an external acousto-optic deflector which produces series of short pulses. Using a drum camera for high speed photography, we achieved a temporal resolution of10 kHz and a spatial resolution of better than2 points/mm². Velocities could be determined without directional ambiguity in a range from2 m/s to30 m/s.     

Time resolved laser-induced plasma dynamics

The structure and evolution of the laser-induced vapor plume and shockwave were measured from femtosecond time resolved shadowgraph images. By changing the wavelength of the probe beam (400 and 800 nm), differences in the opacity of the vapor plume were measured as a function of delay time from the ablation laser pulse. The evolution of the temperature and electron number density during and after the ablation laser pulse were determined and compared for ablation in argon and helium background gases. A laser supported detonation wave (LSD) observed for ablation in argon, blocks the incoming laser energy and generates a high-pressure region above the vapor plume.     

Time resolved photodissociation of small peptide ions

A new instrument has been constructed whose purpose is to study time-resolved photodissociation (TRPD) of small peptide ions. Laser desorption of neutral peptides is combined with laser photoionization in an ion trap followed by thermalization, laser photodissociation and time of flight mass analysis. Ionization and excitation take place through an aromatic chromophore at the C-terminus of the peptide whereas dissociation produces the immonium ion at the N-terminus. The long-range purpose is to uncover the role of IVR in unimolecular fragmentations of peptide radical cations. One avenue is the determination of microcanonical rate constants at a well-defined internal energy E for a series of peptides possessing the same chromophore, undergoing the same fragmentation but having a variable number of degrees of freedom. This paper demonstrates the feasibility of the method and provides the first attempts at rate measurements for the peptide leucyl tyrosine (LeuTyr). Received 6 January 2002 Published online 13 September 2002     

Time resolved excited state absorption of Mn

Excited state absorption (ESA) of Mn²⁺ in spinel MgAl₂O₄ is investigated in detail. For excitation ps-pulses of 351 nm wavelength from a tripled Nd phosphate glass laser are used. During relaxation down to the lowest excited state ESA is measured for various delay times between exciting pulse and probe pulse. The resulting absorption spectra are interpreted in terms of the Mn²⁺ configurational model.     

TDPAC study of Cd-doped SnO

The combination of hyperfine techniques and ab initio calculations has been shown to be a powerful tool to unravel structural and electronic characterizations of impurities in solids. A recent example has been the study of Cd-doped SnO, where ab initio calculations questioned previous TDPAC assignments of the electric-field gradient (EFG) in ¹¹¹In-implanted Sn-O thin films. Here we present new TDPAC experiments at ¹¹¹In-difused polycrystalline SnO. A reversible temperature dependence of the EFG was observed in the range 295–900 K. The TDPAC results were compared with theoretical calculations performed with the full-potential linearized augmented plane wave (FP-LAPW) method, in the framework of the density functional theory. Through the comparison with the theoretical results, we infer that different electronic surroundings around Cd impurities can coexist in the SnO sample.     

Mass attenuation coefficients for n-type InSe, InSe:Gd, InSe:Ho and InSe:Er single crystals

Measurements have been made to determine the mass attenuation coefficients of undoped n-type InSe, and Gd, Ho, Er doped n-InSe single crystals using a Si(Li) detector in the energy region 15.746–40.930 keV X-ray energies with energy dispersive X-ray fluorescence systems. InSe, InSe:Gd, InSe:Ho and InSe:Er single crystals were grown by using the stockbarger method. The measured values are graphically compared with the theoretical ones obtained using WinXcom.     

Time resolved particle dynamics in granular convection

We present an experimental study of the movement of individual particles in a layer of vertically shaken granular material. High-speed imaging allows us to investigate the motion of beads within one vibration period. This motion consists mainly of vertical jumps, and a global ordered drift. The analysis of the system movement as a whole reveals that the observed bifurcation in the flight time is not adequately described by the Inelastic Bouncing Ball Model. Near the bifurcation point, friction plays an important role, and the branches of the bifurcation do not diverge as the control parameter is increased. By fitting the grains trajectories near the wall it is possible to quantify the effective acceleration acting on them. A comparison of the mass centre flying time and the flying time determined for the grains near the wall exposes the underlying mechanism that causes the downward flow.     

Time resolved spectroscopy with femtosecond soft-x-ray pulses

The most challenging application of time resolved spectroscopy is to directly observe the structural and electronic dynamics. Here we present the combination of x-ray absorption spectroscopy with laser driven x-ray sources, offering atomic spatial and temporal resolution. Our new approaches for optimization of laser driven x-ray sources resulted in the demonstration of spatially coherent sub-20 fs x-ray pulses in a range up to several keV. We excited polycrystalline silicon with an ultrashort laser pulse and characterized the collective motion of atoms with time resolved x-ray absorption spectroscopy at a temporal resolution of less than 20 fs. Finally, we have shown the feasibility of probing the dynamics of the electronic structure of silicon and carbon with near edge x-ray absorption spectroscopy.     

Time resolved spectroscopic studies of a FXR discharge

Time resolved spectroscopic studies of some electrode material lines and an impurity line have been performed in a flash X-ray (FXR) discharge. The results indicate that the breakdown takes place in impurities and adsorbed gases released from the electrodes. Thereafter, a front of anode material propagating with a velocity of (1–2)×10⁶ cm/sec moves towards the cathode. A cloud of cathode material is localized outside the cathode during an early stage of the discharge. The anode front and the cathode cloud penetrate each other after current maximum and a “metallic arc” is formed between the electrodes     

Time resolved luminescence of CdS at high excitation

We report a study at low temperature of the time resolved luminescence of CdS, excited by two photon absorption. Concerning the so called EHP-LO and P bands, we confirm our results previously obtained on CdSe[1, 2]. (a) At high excitation a broad band (peak position at λ > 495 nm) occurs due to radiative recombination in an electron hole plasma, assisted by the emission of one LO phonon. (b) The simultaneous kinetics of the P line (λ ? 490.5 nm) and A-LO line (λ ? 492.5 nm) are conflicting with the interpretation of the P line as resulting of radiative exciton-exciton collisions. We interpret the P line as due to biexciton recombination.We have studied the luminescence in the (I₂-I₁) region (486nm < λ < 490nm) at low excitation. We observe clearly the following, (a) A broad band (488 nm < λ < 490.5 nm) which corresponds to the gain observed in previous experiments of pulse and probe spectroscopy and interpreted as direct recombination in an electron hole liquid (EHL). (b) After the disappearance of the EHL band, one single line (M_D), which shifts continuously towards the I₂ position during the time resolved kinetics. We suggest it to be connected with the high excitation effect on donor impurities (bound polyexcitons).     

Time resolved scattering relaxation mechanisms of microcavity polaritons

We study the polariton relaxation dynamics for different scattering mechanisms as: Phonon and electron scattering procesess. The relaxation polariton is obtained at very short times by solving the Boltzman equation. Instead of the well-known relaxation process by phonons, we show that the bottleneck effect relaxes to the ground state more efficiently at low pump power intensity when the electron relaxation process is included. In this way, we clearly demonstrate that different relaxation times exist, for which any of these two mechanism is more efficient to relax the polariton population to the ground state.     

时空分辨平焦场光栅谱仪

利用2 400 lp/mm或1 200 lp/mm的平焦场光栅谱仪、门控宽微带X光单分幅相机及可见光CCD记录系统建立了一套时空分辨平焦场谱仪X光谱诊断系统。介绍了该谱仪系统的结构、工作原理和实验调试方法。利用该谱仪在星光激光装置上进行了时间分辨铝等离子体发射谱线的实验测量,获得了清晰的时间分辨铝等离子体谱线。在神光Ⅱ装置上初步观测到了时空分辨铝样品吸收谱,谱分辨为0.02～0.05nm。     

Z-pinch X射线时间分辨多幅图像诊断系统

 介绍了为“强光一号”设计的ns级时间分辨软X射线多幅图像诊断系统，分析了系统的主要性能指标,给出并分析了利用该系统诊断“强光一号”高功率脉冲Z pinch等离子体辐射源的最新的实验结果。     

Time resolved spectroscopic NMR imaging using hyperpolarized Xe

We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized ¹²⁹Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol.