Fluorescence kinetics of flavin adenine dinucleotide in different microenvironments

Fluorescence kinetics of flavin adenine dinucleotide was measured in a wide time and spectral range in different media, affecting its intra- end extramolecular interactions, and analyzed by a new method based on compressed sensing

Ultrafast electronic and lattice dynamics in laser-excited crystalline bismuth

Femtosecond spectroscopy is applied to study transient electronic and lattice processes in bismuth. Components with relaxation times of 1 ps, 7 ps and ~ 1 ns are detected in the photoinduced reflectivity response of the crystal. To facilitate the assignment of the observed relaxation to the decay of particular excited electronic states we use pump pulses with central wavelengths ranging from 400 nm to 2.3 mum. Additionally, we examine the variation of parameters of coherent A1g phonons upon the change of excitation and probing conditions. Data analysis reveals a significant wavevector dependence of electron-hole and electron- phonon coupling strength along \Gamma--T direction of the Brillouin zone.Comment: 19 pages, 9 figure

Self-phase modulation of a single-cycle THz pulse

We demonstrate self-phase modulation (SPM) of a single-cycle THz pulse in a semiconductor, using bulk n-GaAs as a model system. The SPM arises from the heating of free electrons in the electric field of the THz pulse. Electron heating leads to an ultrafast reduction of the plasma frequency, which results in a strong modification of the THz-range dielectric function of the material. THz SPM is observed directly in the time domain as a characteristic reshaping of single-cycle THz pulse. In the frequency domain, it corresponds to a strong frequency-dependent refractive index nonlinearity of n-GaAs, which is found to be both positive and negative within the broad spectrum of the THz pulse. The spectral position of zero nonlinearity is defined by the electron momentum relaxation rate. Nonlinear spectral broadening and compression of the single-cycle THz pulse was also observed

Quantum-dynamical Modeling of the Rydberg to Valence Excited-State Internal Conversion in Cyclobutanone and Cyclopentanone

In this paper we present 4-state, 5-dimensional Vibronic Coupling Hamiltonians for cyclobutanone and cyclopentanone. Wave packet calculations using these Hamiltonians reveal that for cyclobutanone the (n,3s) to (n,π*) internal conversion involves direct motion in nuclear modes coupling the two states leading to fast population transfer. For cyclopentanone, internal vibrational energy redistribution is a bottleneck for activating reactive nuclear modes leading to slower population transfer

Metamaterial-Enhanced Nonlinear Terahertz Spectroscopy

We demonstrate large nonlinear terahertz responses in the gaps of metamaterial split ring resonators in several materials and use nonlinear THz transmission and THz-pump/THz-probe spectroscopy to study the nonlinear responses and dynamics. We use the field enhancement in the SRR gaps to initiate high-field phenomena at lower incident fields. In vanadium dioxide, we drive the insulator-to-metal phase transition with high-field THz radiation. The film conductivity increases by over two orders of magnitude and the phase transition occurs on a several picosecond timescale. In gallium arsenide, we observe high-field transport phenomena, including mobility saturation and impact ionization. The carrier density increases by up to ten orders of magnitude at high fields. At the highest fields, we demonstrate THz-induced damage in both vanadium dioxide and gallium arsenide.United States. Dept. of Energy (DOE-BES, grant DE-FG02- 09ER46643)United States. Office of Naval Research (ONR Grant No. N00014-09-1-1103

Success or failure of primary second/foreign language programmes in Asia: What do the data tell us?

Primary school second/foreign language (SL/FL) programmes in Asia, as well as in other parts of the world, are becoming more common, with many targeting English as the SL or FL. The pressures for such English language programmes come from top-down notions that in a globalised world English is required for societies to be competitive, especially with Asian neighbours, and bottom-up pressures from parents who see English as the key to educational success for their children. In many polities, these forces have resulted in support for policies that introduce early primary school English teaching curricula for all students and have led to parents spending large sums of money on private tutoring or out-of-school tuition. This study reviews the results of nine language planning studies from the Asian region that set out to examine questions such as 'Is this trend towards early primary SL or FL education (mainly English) realistic or is it unattainable and a waste of resources? Do children really benefit from these programmes? What needs to be done to foster learners' success?' These issues are viewed from a language planning and policy perspective through an examination of the language-in-education policy types required for the development of successful programmes. The policies of a number of Asian countries are used as case studies to illustrate this issue

Photomixing for Coherent Retrieval of THz Waveforms from a Frequency Multiplier

THz waveforms generated with an electronic frequency multiplier are sampled with a heterodyne detection technique using a LTG-GaAs photomixer and the optical beat of two near-infrared lasers

Nonlinear Terahertz Spectroscopy in Solids with Single-Cycle Terahertz Pulses

We present novel generation methods of intense terahertz single cycle pulses. The Cherenkov scheme with tilted wave-front technique in the LiNbO3 crystal gives us the maximum electric field larger than 1 MV/cm, which ponderomotive energy is as large as 10 eV. The ponderomotive energy is strong enough to ionize bound electronic states in solids such as donors and accepters and easy to induce nonlinear optical effects in solids

Ultrafast Charge Separation Dynamics of Twisted Intramolecular Charge Transfer State (TICT) in Coumarin Dye Sensitized TiO 2

Ultrafast transient spectroscopy of 7-diethyl amino coumarin 3-carboxylic acid (D-1421) sensitized TiO2 film reveals that TICT states facilitate higher charge separation and slow recombination and proved to be new route to design higher efficient solar cell