Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F27: Focus Session: Emerging Ultrafast Technologies III |
Hide Abstracts |
Sponsoring Units: DCP Chair: Jennifer Ogilvie, University of Michigan Room: 204B |
Tuesday, March 3, 2015 8:00AM - 8:36AM |
F27.00001: Anti-correlated vibrations drive fast non-adiabatic light harvesting Invited Speaker: David Jonas We have recently shown that intramolecular vibrations shared across pigments can drive electronic energy transfer beyond the Born-Oppenheimer framework developed by Forster. The key features of this mechanism are a small change in vibrational equilibrium (less than the zero point amplitude) upon electronic excitation of the pigments and vibrational resonance with the adiabatic electronic energy gap. For identical pigments, delocalized, anti-correlated vibrations increase the speed of energy transfer. The same anti-correlated vibrations are excited by an electronically enhanced Raman process on the ground electronic state of photosynthetic antennas, and these vibrational wavepackets generate all of the reported signatures of photosynthetic energy transfer in femtosecond two-dimensional Fourier transform spectra. The talk will discuss how these results are generalized for differences between donor and acceptor and for multiple vibrations. [Preview Abstract] |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F27.00002: Two-Dimensional Line Shapes in Electronic-Vibrational Spectroscopy as a Measure of Correlated Spectral Dynamics of Electronic and Vibrational Degrees of Freedom Nicholas Lewis, Hui Dong, Thomas Oliver, Graham Fleming 2D optical spectroscopies in many different frequency regimes have been useful to study the correlated spectral behavior for many different types of system degrees of freedom. The slope of the center-line of a feature in 2D electronic and 2D infrared spectroscopy has been shown to provide detailed information about the correlation functions that describe the system-bath coupling for the system degrees of freedom.\footnote{K. Kwac and M. Cho, \textbf{J. Phys. Chem. A} 107, 5903} Recently, we have demonstrated a new spectroscopic technique, 2D electronic-vibrational spectroscopy, that is capable of directly measuring the correlation between spectral motion of the electronic and vibrational degrees of freedom.\footnote{T.A.A. Oliver, N.H.C. Lewis and G.R. Fleming, \textbf{PNAS} 111, 0927} Here we demonstrate that the center-line slope of a 2DEV resonance can be directly related to the correlation function for the vibrational degrees of freedom on the electronic excited state. We show experimentally that this can be observed in 2DEV spectra of the dye DTTCI. Finally, we show how 2DEV spectra can be used to directly measure the strength of system-bath coupling for the vibrational degrees of freedom on the electronic excited state versus those on the electronic ground state. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:24AM |
F27.00003: Femtosecond Stimulated Raman Spectroscopy by Six-Wave Mixing Invited Speaker: Andrew Moran Knowledge of the structural changes that accompany photochemical reactions has motivated the development of a wide variety of time-resolved vibrational spectroscopies. For example, a technique known as femtosecond stimulated Raman spectroscopy (FSRS) has yielded important insights into numerous photochemical processes in the past 10-15 years. Simultaneous probing of all resonances in the fingerprint region of the vibrational spectrum and sensitivity to dynamics on the 100-fs time scale are the primary selling points for the FSRS technique. Despite its utility, FSRS is challenged by a large background of residual laser light and lower-order nonlinearities. In this talk, I will introduce a newly developed FSRS experiment in which five laser beams are used eliminate the background of residual laser light and lower-order nonlinearities present in the traditional three-beam FSRS geometry. Applications to photodissociation reactions in triiodide and heme proteins will be discussed. It is envisioned that this approach will be useful for investigating photoinduced dynamics in a wide variety of condensed phase systems. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 9:36AM |
F27.00004: Quantum Process Tomography by 2D Fluorescence Spectroscopy Leonardo A. Pachon, Alan Aspuru-Guzik Characterization of quantum dynamics is one of the most important steps toward the implementation of any quantum technology and therefore, it is of fundamental relevance. Traditionally, dynamics are studied for particular initial preparations and hence, only partial information about the underlying physical processes is obtained. To overcome this drawback, a variety of proposals based on spectroscopic techniques have been suggested. Quantum Processes Tomography allows for the experimental reconstruction of the dynamics regardless the initial condition. Despite the success of QTP, the spectroscopic techniques they are based on require large samples to enhance the non-linear signal. Hence, particular features of the dynamics and realistic time scales are hidden by the incoherent average over the large structural and electronic heterogeneity. Based on recent progress on non-linear spectroscopies using collinear phase-modulated ultra-short pulses, which are suitable for single molecule spectroscopy, a formulation of single molecule QPT with classical light is provided here. This technique is applied to recover the dynamics of a model dimer. The single molecule character of this technique predicts longer coherence times than those techniques based on the phase-matching condition. [Preview Abstract] |
Tuesday, March 3, 2015 9:36AM - 10:12AM |
F27.00005: Ultrafast 2D Fluorescence Spectroscopy using Spectrally Entangled Photon Pairs Invited Speaker: Michael Raymer We propose entangled photon-pair two-dimensional fluorescence spectroscopy (EPP-2DFS) to probe the nonlinear electronic response of molecular systems. [1] The method, inspired by results in [2], uses a technique from quantum optics---a separated two-photon (Franson) interferometer, which generates time-delayed packets of time-frequency-entangled photon pairs. This interferometer is incorporated into the framework of a fluorescence-detected 2D optical spectroscopic experiment [3]. The continuous stream of entangled photons are phase-modulated in the interferometer, and used to excite a two-photon-absorbing sample, whose excited-state population is selectively detected by simultaneously monitoring the sample fluorescence and the transmitted exciting fields. In comparison to standard `classical' 2DFS techniques using coherent laser pulses and standard pulse-scanning sequences, advantages of this scheme include the suppression of uncorrelated background signals, the suppression of diagonal 2D spectral features, the enhancement and narrowing of off -diagonal spectral cross-peaks that contain information about electronic coupling, and the possibility for enhancement of simultaneous time-and-frequency resolution, including spectral selectivity within an inhomogeneously broadened distribution. These effects arise from the properties of parametric down-conversion light source, which effectively creates a different interaction-scanning protocol than in standard laser-pulse scanning. We numerically simulate the EPP-2DFS observable for the case of an electronically coupled molecular dimer. The EPP-2DFS spectrum is greatly simplified in comparison to its standard classical 2D counterpart. Our results indicate that EPP-2DFS can provide previously unattainable resolution to extract model Hamiltonian parameters from electronically coupled molecular dimers. \\[4pt] [1] M.G Raymer, A. H. Marcus, J. R. Widom, D. L. P. Vitullo, Entangled Photon-Pair Two-Dimensional Fluorescence Spectroscopy (EPP-2DFS), J. Phys. Chem. B, 117, 15559 (2013) \\[0pt] [2] O. Roslyak, S. Mukamel, Multidimensional pump-probe spectroscopy with entangled twin-photon states. Phys. Rev. A, 79, 063409 (2009) \\[0pt] [3] P. F. Tekavec, G. A. Lott, A. H. Marcus, Fluorescence-Detected Two-Dimensional Electronic Coherence Spectroscopy by Acousto-Optic Phase Modulation, J. Chem. Phys. 127, 214307 (2007) [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F27.00006: Surface Sum Frequency Generation of III-V Semiconductors Zhenyu Zhang, Jisun Kim, Rami Khoury, E.W. Plummer, Louis Haber Optical sum frequency generation (SFG) is a well-established technique for surface and interface studies but its use has been limited mainly to centrosymmetric materials so far. Here, we demonstrate that femtosecond broadband SFG spectroscopy has the ability to identify surface molecular vibrations on the archetypical non-centrosymmetric semiconductor GaAs (001), in which the bulk SFG signal typically dominates over surface SFG contributions. Azimuthal angle dependence of the second order SFG nonlinear response from GaAs (001) surface in the reflection geometry in vacuum for all eight polarization combinations are detected and analyzed. The results agree with and extend upon previous second harmonic generation (SHG) studies and phenomenological analysis. In addition, carbon monoxide and methanol are employed as molecular-markers on the GaAs (001) surfaces. The C-O stretching mode of carbon monoxide and the methyl group stretching modes of methanol are clearly observed even though the bulk contribution dominates the SFG signal. Coherent heterodyne interference is proposed as the mechanism for the surface signal enhancement. Two other zinc blende type III-V semiconductors, GaP and GaSb, are also studied and compared. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F27.00007: Probing Molecular Organization and Electronic Dynamics at Buried Organic Interfaces Sean Roberts Organic semiconductors are a promising class of materials due to their ability to meld the charge transport capabilities of semiconductors with many of the processing advantages of plastics. In thin film organic devices, interfacial charge transfer often comprises a crucial step in device operation. As molecular materials, the density of states within organic semiconductors often reflect their intermolecular organization. Truncation of the bulk structure of an organic semiconductor at an interface with another material can lead to substantial changes in the density of states near the interface that can significantly impact rates for interfacial charge and energy transfer. Here, we will present the results of experiments that utilize electronic sum frequency generation (ESFG) to probe buried interfaces in these materials. Within the electric dipole approximation, ESFG is only sensitive to regions of a sample that experience a breakage of symmetry, which occurs naturally at material interfaces. Through modeling of signals measured for thin organic films using a transfer matrix-based formalism, signals from buried interfaces between two materials can be isolated and used to uncover the interfacial density of states. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F27.00008: Stimulated Second Harmonic Generation for High-Sensitivity Interfacial Spectroscopy and Imaging Aaron Goodman, William Tisdale Second-order nonlinear optical interactions such as sum- and difference-frequency generation are widely used for bioimaging and as selective probes of interfacial environments. However, inefficient nonlinear optical conversion often leads to poor signal-to-noise ratios and long signal acquisition times. Here, we demonstrate the dramatic enhancement of weak second-order nonlinear optical signals via stimulated sum- and difference-frequency generation. We present a conceptual framework to quantitatively describe the interaction and show that the process is highly sensitive to the relative optical phase of the stimulating field. To emphasize the utility of the technique, we demonstrate stimulated enhancement of second harmonic generation (SHG) from bovine collagen-I fibrils. Using a stimulating pulse fluence of only 3 nJ/cm$^2$, we obtain an SHG enhancement of $>$ 10$^4$ relative to the spontaneous signal. The stimulated enhancement is greatest in situations where spontaneous signals are the weakest - such as low laser power, small sample volume, and weak nonlinear susceptibility - emphasizing the importance of this technique for improving signal-to-noise ratios in biological imaging and interfacial spectroscopy. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700