Sub-optical-cycle light-matter energy transfer in molecular vibrational spectroscopy
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Abstract The evolution of ultrafast-laser technology has steadily advanced the level of detail in studies of light-matter interactions. Here, we employ electric-field-resolved spectroscopy and quantum-chemical modelling to precisely measure and describe the complete coherent energy transfer between octave-spanning mid-infrared waveforms and vibrating molecules in aqueous solution. The sub-optical-cycle temporal resolution of our technique reveals alternating absorption and (stimulated) emission on a few-femtosecond time scale. This behaviour can only be captured when effects beyond the rotating wave approximation (RWA) are included in simulations using first-order time-dependent perturbation theory. At a timescale of femtoseconds to picoseconds, other energy transfer processes are observed, namely optical-phase-dependent coherent transients and the dephasing of the vibrations of resonantly excited methylsulfonylmethane (DMSO2) molecules due to their motion through varying environments in the solvent. Ab-initio modelling using density functional theory traces these dynamic processes back to molecular-scale sample properties. The absorbed and coherently re-emitted fractions of the optical energy impinging on the sample can be used as performance metrics for spectroscopic techniques that allow for the separation of absorption and re-emission in time and/or in space. The extension of our study to nonlinear interrogation of higher-order susceptibilities is fathomable with state-of-the-art lasers in the near future.Keywords:
Picosecond
Dephasing
Femtochemistry
Dephasing
Picosecond
Vibrational energy relaxation
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An analysis is made of the possibility of employing picosecond absorption spectroscopy based on continuously tunable excitation and probe sources in the investigation of complex kinetic processes. The results are presented of an investigation of various cyanine dyes. Calculations are made of the extinction coefficient of the excited state of one of the dyes. It is shown that the photoisomer 1,1'-diethyl-2,2'-monocarbocyanine, not observed previously, is formed within less than 50 psec.
Picosecond
Cyanine
Molar absorptivity
Extinction (optical mineralogy)
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A survey of picosecond techniques for the study of vibrational dynamics in liquids is presented. The coherent Raman scattering of ultrashort probing pulses is discussed in more detail. A novel k -vector technique investigates the dephasing of a molecular subgroup selected from a distribution of vibrational frequencies. Experimental examples are reported which yield the (homogeneous) dephasing time and, for the first time, give direct evidence of inhomogeneous line broadening in several cases. Special emphasis is laid on the physical interpretation of the picosecond results.
Dephasing
Picosecond
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The advent of ultrashort optical pulses used in conjuntion with the electro-optic effect made possible the temporal analysis of electrical phenomena on the pico- and sub-picosecond time scale 1 , 2 . We now report on two new developments made with this system.
Picosecond
Characterization
Ultrafast optics
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The recently introduced PROUD technique for ultrashort pulse characterization is extended down to the picosecond regime using a well-characterized temporal stretcher (e.g. dispersive optical fiber). The proposed method is demonstrated by precisely characterizing optical pulses ranging from 4∼20-ps with microwatts average powers..
Picosecond
Characterization
Ultrafast optics
Ranging
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Picosecond
Nanosecond
Absorption band
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Dephasing
Picosecond
Homogeneous broadening
Echo (communications protocol)
Line (geometry)
Atmospheric temperature range
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Picosecond
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Abstract Using picosecond CARS the dephasing rate of the ν 1 ‐mode of CS 2 is investigated in several solvents and in the neat liquid. A large pressure effect (factor of ≤3) is reported for the range 0 to 4 kbar similar to spontaneous Raman results. For an extended interval of 160 to 450 K, a non‐monotonic temperature dependence is reported for the first time and compared with theoretical models. — A novel non‐degenerate CARS spectrometer is described with 80 fs time resolution and improved measuring accuracy. A dephasing time of T 2 = 608 ± 6 fs is reported for the ν 1 mode of neat acetone of 293 K; negligible inhomogeneous broadening (< 1%) is indicated by the scattering data for this vibration.
Dephasing
Picosecond
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