1,721,140 research outputs found
Inverse Transform in Resonance Raman Scattering: An Iterative Approach
No full textA new inverse transform procedure is presented that calculates the absorption band (ABS) from an experimental Raman excitation profile (REP). An iterative solution is sought for an integral Hilbert transform relation between the phase of a complex REP polarizability function and its logarithmic magnitude. The inverse transform is tested for model REP's which are synthesized by the forward transform of a known ABS, that of the azulene S1 band. An exact ABS is recovered irrespective of the starting ABS when sufficient iterations are performed.11Nsciescopu
Cavity-dumped femtosecond optical parametric oscillator based on periodically poled stoichiometric lithium tantalate
No full textA synchronously pumped cavity-dumped femtosecond optical parametric oscillator (OPO) based on a periodically poled stoichiometric lithium tantalate (PPSLT) crystal is reported. The OPO runs in positive group velocity dispersion (GVD) mode to deliver high pulse energy at high repetition rate. It delivers pulse energy over 130 nJ up to 500 kHz and 70 nJ at 1 MHz of repetition rate at 1100 nm. Pulse duration is as short as 42 fs, and the OPO is tunable in the near infrared region from 1050 to 1200 nm. Dispersion property of the OPO was also explored. The cavity-dumped output carries a positive GVD, which can be compensated easily by an external prism pair, and large negative third order dispersion (TOD), which results in a pedestal in the pulse shape. Approaches to obtain clean pulse shape by reducing the large TOD are proposed.111Nsciescopu
Diffractive optics based three-pulse photon echo peak shift studies of spectral diffusion in polar liquids: Evidence for long lived frequency correlations
No full textWe report a three-pulse photon echo peak shift (3PEPS) apparatus adopting a diffractive beam splitter to generate triplets of femtosecond pulses with tilted wave front, which enhances the overlap over the entire aperture in a noncollinear geometry while preserving femtosecond pulse duration. The apparatus provides highly reproducible 3PEPS data including the long time peak shift, a critical parameter to recognize the spectral inhomogeneity in condensed phases. To demonstrate the high performance of our setup and to examine the inhomogeneous line broadening in liquids, we measured 3PEPS of a carbocyanine dye IR125 in several solvents. The solvation dynamics becomes slower for IR125 compared to the typical values reported previously probably due to the multipolar nature of the excitation in this large and flexible probe molecule. More importantly, inhomogeneity was observed unambiguously in all solvents, and it is excitation energy dependent. It was speculated that slow dielectric relaxation and conformational heterogeneity may be responsible for the inhomogeneity. (C) 2009 American Institute of Physics. [doi:10.1063/1.3253971]open1176sciescopu
Photophysical Model of 10-Hydroxybenzo[h]quinoline: Internal Conversion and Excited State Intramolecular Proton Transfer
Full text linkPhotophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the similar to 300 fs component observed frequently in ESIPT dynamics arises from the S-2 -> S-1 internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S-1 state to the keto isomer in S-2 state.X1166Ysciescopu
Nuclear dynamics in electronic ground and excited states probed by spectrally resolved four wave mixing
No full textTime-resolved ground-state bleach and excited-state stimulated emission spectra have been measured for indocyanine green dissolved in methanol by employing spectrally resolved four wave mixing (SRFWM). The separation of the SRFWM signals into the ground-state bleach and excited-state stimulated emission contributions allows observation of intramolecular vibrational wave packet motions and intermolecular solvation dynamics upon impulsive excitation, while the molecule resides either in the ground or in the excited state. Frequencies of the indocyanine green intramolecular vibrational modes in the ground and excited states are practically the same. Vibrational dephasing times in the excited state range from a few hundred fs to similar to2 ps, and they are consistently shorter than those in the ground state. When excitation frequency is centered near the 0-0 transition, center frequencies of the stimulated emission redshift due to solvation of the excited state in nonequilibrium solvent configuration, whereas those of the ground-state bleach blueshift due to equilibrium fluctuation of the solvent molecules around the chromophore in the ground state. At early times, the solvation function obtained from the time-resolved ground-state bleach spectra is slower than the solvation function obtained from the time-resolved excited-state stimulated emission spectra.(C) 2002 American Institute of Physics.open111211sciescopu
Ultrafast time-resolved fluorescence by two photon absorption excitation
No full textWe report a time-resolved fluorescence apparatus utilizing fluorescence upconversion by noncollinear sum frequency generation and two photon absorption as an excitation. Near perfect time-resolution is achieved with 20 fs pulses to give the instrument response of 33 fs (FWHM) over the entire fluorescence wavelength for a 100 mu m thick mixing crystal. Through experiments and numerical simulations, it is shown that 40 fs time-resolution can be obtained even for a 580 mu m thick mixing crystal at a fluorescence wavelength longer than 500 nm. (C) 2008 Optical Society of AmericaX1122sciescopu
Near-infrared cavity-dumped femtosecond optical parametric oscillator
No full textWe demonstrate a high-energy near-infrared cavity-dumped femtosecond optical parametric oscillator (OPO) based on periodically poled lithium niobate. The laser generates 90 nJ pulses at a repetition rate of up to 1 MHz when synchronously pumped by 800 mW output from a femtosecond Ti:sapphire laser. The laser is broadly tunable from 1.0 to 1.5 mu m in the signal branch, with a pulse duration of < 60 fs at 1.2 mu m. High intracavity power is achieved by running the laser in the regime of positive group-velocity dispersion. (c) 2005 Optical Society of America.X1115sciescopu
Coherent excited state intramolecular proton transfer probed by time-resolved fluorescence
No full textAn ultra-fast chemical reaction can act as an impulsive excitation of the vibrations. Excited state intramolecular proton transfer in 10-hydroxybenzo[h]quinoline proceeds in 13 fs. As a result, product vibrational modes with their periods longer than (13 x 2) fs are coherently excited in the product potential surface, which can be observed most unambiguously by the oscillations in the time-resolved fluorescence signal of the product keto isomer.open115657sciescopu
Coherent Nuclear Wave Packets in Q States by Ultrafast Internal Conversions in Free Base Tetraphenylporphyrin
No full textPersistence of vibrational coherence in electronic transition has been noted especially in biochemical systems. Here, we report the dynamics between electronic excited states in free base tetraphenylporphyrin (H2TPP) by time-resolved fluorescence with high time resolution. Following the photoexcitation of the B state, ultrafast internal conversion occurs to the Q(x) state directly as well as via the Q(y) state. Unique and distinct coherent nuclear wave packet motions in the Q(x) and Q(y) states are observed through the modulation of the fluorescence intensity in time. The instant, serial internal conversions from the B to the Q(y) and Q(x) states generate the coherent wave packets. Theory and experiment show that the observed vibrational modes involve the out-of-plane vibrations of the porphyrin ring that are strongly coupled to the internal conversion of H2TPP.1110sciescopu
Noncollinear phase matching in fluorescence upconversion
No full textWe investigate noncollinear sum-frequency generation in a time-resolved fluorescence upconversion experiment to eliminate group-velocity mismatch (GVM), a major mechanism that deteriorates time resolution. The noncollinear geometry inherently causes phase-front mismatch (PFM) that also spoils time resolution. The effects of GVM and PFM on the time resolution are studied by numerical calculations and experiments. Based on the investigation, a fluorescence upconversion apparatus with time resolution better than 45 fs (FWHM) is demonstrated. (C) 2005 Optical Society of America.X1145sciescopu
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