Lev Chuntonov - Academia.edu (original) (raw)
Papers by Lev Chuntonov
Journal of Physical Chemistry Letters, Jul 10, 2017
Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecul... more Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecular structure and ultrafast dynamics in 1-100 m µ thick bulk samples. Confinement of molecules to surfaces, gaps, crevices, and other topographic features, frequently encountered on the nanometer length scale, significantly alters their structure and dynamics, affecting physical and chemical properties. Amplification of 2DIR signals by the plasmon-enhanced fields around metal nanostructures can permit structural and dynamics measurements of the confined molecules. Fano resonances, induced by the interaction between laser pulses, plasmon, and vibrational modes significantly distort 2D lineshapes. For different detuning from plasmon resonance, the interference between multiple signal components leads to different lineshape asymmetry, which we demonstrate on a set of linear absorption, transient absorption, and 2DIR spectra. An intuitive model used to describe experimental data points onto the interference's origin. Our results will facilitate the application of surface-enhanced 2DIR spectroscopy for studies of molecular structure and dynamics in nano-confined environment.
ACS Nano, May 4, 2018
Infrared gold antennas localize enhanced near-fields close to the metal surface, when excited at ... more Infrared gold antennas localize enhanced near-fields close to the metal surface, when excited at the frequency of their plasmon resonance, and amplify vibrational signals from the nearby molecules. We study the dependence of the signal enhancement on the thickness of a polymer film containing vibrational chromophores, deposited on the antenna array, using linear (FTIR) and third-order femtosecond vibrational spectroscopy (transient absorption and 2DIR). Our results show that for a film thickness beyond only a few nanometers, the near-field interaction is not sufficient to account for the magnitude of the observed signal, which nevertheless has a clear Fano lineshape, suggesting a radiative origin of the molecule-plasmon interaction. The mutual radiative damping of plasmonic and molecular transitions leads to the spectroscopic signal of a molecular vibrational excitation to be enhanced by up to a factor of 50 in the case of linear spectroscopy and over 2000 in the case of third-order spectroscopy. Qualitative explanation for the observed effect is given by the extended coupled oscillator model, which takes into account both near-field and radiative interactions between the plasmonic and molecular transitions.
Chemical Physics, 2017
Vibrational energy transfer driven by anharmonicity is the major mechanism of energy dissipation ... more Vibrational energy transfer driven by anharmonicity is the major mechanism of energy dissipation in polyatomic molecules and in molecules embedded in condensed phase environment. Energy transfer pathways are sensitive to the particular intra-molecular structure as well as to specific interactions between the molecule and its environment, and their identification is a challenging many-body problem. This work introduces a theoretical approach which enables to identify the dominant pathways for specified initial excitations, by screening the different possible relaxation channels. For each channel, the many-body Hamiltonian is mapped onto a respective all-vibrational Spin-Boson Hamiltonian, expressed in terms of the harmonic frequencies and the anharmonic coupling parameters obtained from the electronic structure of the molecule in its environment. A focus is given on the formulation of the relaxation rates when different limits of perturbation theory apply. In these cases the proposed Spin-Boson Screening approach becomes especially powerful.
The Journal of Chemical Physics, 2022
High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime... more High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime form polariton states by means of strong coupling to molecular vibrations. We studied polaritons formed by carbonyl stretching modes of (poly)methyl methacrylate on resonant antenna arrays using femtosecond 2DIR spectroscopy. At a normal incidence of excitation light, doubly degenerate antenna-lattice resonances (ALRs) form two polariton states: a lower polariton and an upper polariton. At an off-normal incidence geometry of 2DIR experiments, the ALR degeneracy is lifted and, consequently, the polariton energies are split. We spectrally resolved and tracked the time-dependent evolution of a cross-peak signal associated with the excitation of reservoir states and the unidirectional transfer of the excess energy to lower polaritons. Bi-exponential decay of the cross-peak suggests that a reversible energy exchange between the bright and dark lower polaritons occurs with a characteristic tr...
The Journal of Physical Chemistry C, 2022
Ultrafast studies of molecular dynamics using femtosecond twodimensional vibrational spectroscopy... more Ultrafast studies of molecular dynamics using femtosecond twodimensional vibrational spectroscopy (2DIR) provide unique insights on molecular interactions. Recently, such studies were extended from bulk samples to molecules on surfaces of noble metals, including disordered and engineered nanostructures. The metal nanostructures provide field enhancement allowing sensitive measurements at interfaces, but they also alter the molecular dynamics. 2DIR measurements at interfaces reveal correlations between vibrational transitions and rates of the vibrational relaxation, dephasing, spectral diffusion, and resonant energy transfer. At the surfaces, molecular dynamics and interaction with the environment can be modified by geometrical constrains associated with tethering, by the interaction between the molecule and the substrate, or by the enhanced near-fields associated with the metal. Interestingly, in many cases, these anticipated effects were found to be absent or fade away already at the microscopic distances away from the surface. Herein, we provide an overview of recent experimental studies in the field.
The Journal of Physical Chemistry B, 2021
A detailed understanding of the molecular structure in nanoparticle ligand capping layers is cruc... more A detailed understanding of the molecular structure in nanoparticle ligand capping layers is crucial for their efficient incorporation into modern scientific and technological applications. Peptide ligands render the nanoparticles as biocompatible materials. Glutathione, a γ-ECG tripeptide, self-assembles into aggregates on the surface of ligand-free silver nanoparticles through intermolecular hydrogen bonding and forms a few nanometer-thick shells. Two-dimensional nonlinear infrared (2DIR) spectroscopy suggests that aggregates adopt a conformation resembling the β-sheet secondary structure. The shell thickness was evaluated with localized surface plasmon resonance spectroscopy and X-ray photoelectron spectroscopy. The amount of glutathione on the surface was obtained with spectrophotometry of a thiol-reactive probe. Our results suggest that the shell consists of ∼15 stacked molecular layers. These values correspond to the inter-sheet distances, which are significantly shorter than those in amyloid fibrils with relatively bulky side chains, but are comparable to glycine-rich silk fibrils, where the side chains are compact. The tight packing of the glutathione layers can be facilitated by hydrogen-bonded carboxylic acid dimers of glycine and the intermolecular salt bridges between the zwitterionic γ-glutamyl groups. The structure of the glutathione aggregates was studied by 2DIR spectroscopy of the amide-I vibrational modes using 13C isotope labeling of the cysteine carbonyl. Isotope dilution experiments revealed the coupling of modes forming vibrational excitons along the cysteine chain. The coupling along the γ-glutamyl exciton chain was estimated from these values. The obtained coupling strengths are slightly lower than those of native β-sheets, yet they appear large enough to point onto an ordered conformation of the peptides within the aggregate. Analysis of the excitons' anharmonicities and the strength of the transition dipole moments generally is in agreement with these observations.
The Journal of Chemical Physics, 2020
Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the fore... more Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the forefront of fundamental chemical and physical research for several decades. Among the spectroscopic observables of the ultrafast dynamics is the pure dephasing of vibrationally excited molecules. Using third-order nonlinear vibrational spectroscopy, including polarization-selective transient grating measurements of vibrational lifetime and orientational diffusion as well as two-dimensional infrared spectroscopy, we determined different individual line shape components of hydroxyl stretching (νOH) excitations in a homologous series of chlorophenols and obtained the corresponding pure dephasing rates. The pure dephasing rates are correlated with vibrational anharmonicity of the νOH mode, which is tuned remotely from the hydroxyl site by changing the position of the chlorine substituents on the phenol ring. We found that in molecules where the hydroxyl group is in its free form, the pure depha...
The Journal of Physical Chemistry Letters, 2018
Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have... more Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have been demonstrated to enhance 2DIR signals by multiple orders of magnitude. We design doubly-degenerate in-plane plasmonic normal modes of the symmetric trimer gap-antenna, which have orthogonal dipole moments excited by light of the appropriate polarization, to
Chemical Reviews, 2018
Plasmonic molecules are small assemblies of nanosized metal particles. Interactions between the p... more Plasmonic molecules are small assemblies of nanosized metal particles. Interactions between the particles modify their optical properties and make them attractive for multiple applications in spectroscopy and sensing. In this review, we focus on basic properties rather than on applications. Plasmonic molecules can be created using either nanofabrication methods or self-assembly techniques in solution. The interaction of plasmonic molecules with light leads to excitations that are classified using the concept of normal modes. The simplest plasmonic molecule is a dimer of particles, and its lowest energy excitation takes the form of a symmetric dipolar mode. More complex excitations take place when a larger number of particles is involved. The gaps between particles in a plasmonic molecule form hotspots in which the electromagnetic field is concentrated. Introducing molecules into these hotspots is the basis of a vast spectrum of enhanced spectroscopies, from surface-enhanced Raman scattering to surface-enhanced fluorescence and others. We show in this review how these spectroscopic methods can be used to characterize the fields around plasmonic molecules. Furthermore, the strong fields can be used to drive new phenomena, from plasmon-induced chemical reactions to strong coupling of quantum emitters with the plasmonic fields. We systematically discuss these phenomena, introducing in each case the theoretical basis as well as recent experimental realizations.
Single Nanoparticles and Single Cells, 2014
Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2014
The simplest plasmonic molecule (PM) is a cluster of 2-3 metal particles. 2. PMs can be generated... more The simplest plasmonic molecule (PM) is a cluster of 2-3 metal particles. 2. PMs can be generated by solution chemistry or nanofabrication. 3. Electromagnetic hot spots intheir gaps enhance Raman scattering or fluorescence. 4. Symmetry of a PM affects its excitations, which can be classified by group theory. 5. PMs can serve as antennas, sensors or quantum cavities interacting with molecules.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
ABSTRACT We demonstrate a light-induced method to enhance, control, and tune two-photon-absorptio... more ABSTRACT We demonstrate a light-induced method to enhance, control, and tune two-photon-absorption in bulk CZT:V crystals. The technique is reversible in real-time, and enhancement scales linearly with control-beam intensity, reaching 2.5 times of the original values.
Physical Review A, 2007
Femtosecond coherent phase control of resonance mediated ͑2+1͒ three-photon absorption is studied... more Femtosecond coherent phase control of resonance mediated ͑2+1͒ three-photon absorption is studied both theoretically and experimentally. The regime is perturbative of third order. The photoexcitation coherently combines elements of both nonresonant and resonance-mediated multiphoton transitions. By proper simple pulse shaping the three-photon absorption in Na is effectively controlled experimentally, enhanced up to ϳ300% of the absorption induced by the transform-limited pulse. It is achieved by phase manipulating intraand intergroup interferences involving two groups of three-photon excitation pathways: ͑i͒ on resonance and ͑ii͒ near resonance with the intermediate resonance state accessed by nonresonant two-photon transition.
The Journal of Physical Chemistry C, 2011
Gold island films displaying localized plasmon properties were prepared by evaporation of just-pe... more Gold island films displaying localized plasmon properties were prepared by evaporation of just-percolated Au films onto glass substrates followed by annealing at g550°C. Annealing induces depercolation and formation of large, singlecrystalline, well-separated islands, partially embedded in the glass. Two dewetting mechanisms were identified, depending on the initial film morphology. The variability of island sizes and shapes provides effective means of tuning the position of the localized surface plasmon resonance (LSPR) band in a wide wavelength range. With an increase in the Au nominal thickness a transition occurs from transducers dominated by absorbance to ones dominated by scattering. Numerical simulations taking into account the shape and size distribution in actual island samples are in agreement with the experimental spectra. Refractive index sensitivity (RIS) measurements at a constant wavelength or at a constant extinction, tailored to the specific transducer, provide superior sensitivity to refractive index change, up to ca. 600 nm RIU À1 in wavelength shift.
Nano Letters, 2013
We show that a hybrid system built of a plasmonic nanoparticle cluster and a single molecule can ... more We show that a hybrid system built of a plasmonic nanoparticle cluster and a single molecule can attain maximal Raman optical activity (ROA), converting linearly polarized light into purely circularly polarized light at the Raman-scattered frequency. In contrast to standard molecular ROA, the effect described here does not involve magnetic modes and is attributed to off-resonance excitation of electric-dipole plasmon modes of the nanoparticle cluster. A model based on a combination of harmonic oscillators excited at the frequency of the Raman-scattered light is shown to successfully capture the physics of the effect.
The Journal of Physical Chemistry Letters, 2013
Coherent dynamics of degenerate quantum states symmetry-broken on the femtosecond timescale is fo... more Coherent dynamics of degenerate quantum states symmetry-broken on the femtosecond timescale is found to exhibit the phenomenon of quantum beats. Frequency-resolved and polarizationselective heterodyned transient grating spectroscopy enabled us to retrieve the oscillation pattern characteristic of the beating in systems undergoing ultrafast dynamical processes. This methodology applies to the general phenomena of coherence dynamics which is important in any ultrafast multidimensional spectroscopy. A particular application to the vibrational spectroscopy of coherence in the degenerate normal modes of the tricyanomethanide anion solvated in water is explored in this study. The relaxation of the cross-polarization transient grating anisotropy is shown to reflect the loss of the vibrational coherence, which is caused by ultrafast dynamics of the water solvation shell.
The Journal of Chemical Physics, 2013
Molecular ions undergoing ultrafast conformational changes on the same time scale of water motion... more Molecular ions undergoing ultrafast conformational changes on the same time scale of water motions are of significant importance in condensed phase dynamics. However, the characterization of systems with fast molecular motions has proven to be both experimentally and theoretically challenging. Here, we report the vibrational dynamics of the non-degenerate (C12,C13)-oxalate anion, an ultrafast rotor, in aqueous solution. The infrared absorption spectrum of the (C12,C13)-oxalate ion in solution reveals two vibrational transitions separated by approximately 40 cm−1 in the 1500–1600 cm−1 region. These two transitions are assigned to vibrational modes mainly localized in each of the carboxylate asymmetric stretch of the ion. Two-dimensional infrared spectra reveal the presence and growth of cross-peaks between these two transitions which are indicative of coupling and population transfer, respectively. A characteristic time of sub-picosecond cross-peaks growth is observed. Ultrafast pump...
Journal of Physical Chemistry Letters, Jul 10, 2017
Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecul... more Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecular structure and ultrafast dynamics in 1-100 m µ thick bulk samples. Confinement of molecules to surfaces, gaps, crevices, and other topographic features, frequently encountered on the nanometer length scale, significantly alters their structure and dynamics, affecting physical and chemical properties. Amplification of 2DIR signals by the plasmon-enhanced fields around metal nanostructures can permit structural and dynamics measurements of the confined molecules. Fano resonances, induced by the interaction between laser pulses, plasmon, and vibrational modes significantly distort 2D lineshapes. For different detuning from plasmon resonance, the interference between multiple signal components leads to different lineshape asymmetry, which we demonstrate on a set of linear absorption, transient absorption, and 2DIR spectra. An intuitive model used to describe experimental data points onto the interference's origin. Our results will facilitate the application of surface-enhanced 2DIR spectroscopy for studies of molecular structure and dynamics in nano-confined environment.
ACS Nano, May 4, 2018
Infrared gold antennas localize enhanced near-fields close to the metal surface, when excited at ... more Infrared gold antennas localize enhanced near-fields close to the metal surface, when excited at the frequency of their plasmon resonance, and amplify vibrational signals from the nearby molecules. We study the dependence of the signal enhancement on the thickness of a polymer film containing vibrational chromophores, deposited on the antenna array, using linear (FTIR) and third-order femtosecond vibrational spectroscopy (transient absorption and 2DIR). Our results show that for a film thickness beyond only a few nanometers, the near-field interaction is not sufficient to account for the magnitude of the observed signal, which nevertheless has a clear Fano lineshape, suggesting a radiative origin of the molecule-plasmon interaction. The mutual radiative damping of plasmonic and molecular transitions leads to the spectroscopic signal of a molecular vibrational excitation to be enhanced by up to a factor of 50 in the case of linear spectroscopy and over 2000 in the case of third-order spectroscopy. Qualitative explanation for the observed effect is given by the extended coupled oscillator model, which takes into account both near-field and radiative interactions between the plasmonic and molecular transitions.
Chemical Physics, 2017
Vibrational energy transfer driven by anharmonicity is the major mechanism of energy dissipation ... more Vibrational energy transfer driven by anharmonicity is the major mechanism of energy dissipation in polyatomic molecules and in molecules embedded in condensed phase environment. Energy transfer pathways are sensitive to the particular intra-molecular structure as well as to specific interactions between the molecule and its environment, and their identification is a challenging many-body problem. This work introduces a theoretical approach which enables to identify the dominant pathways for specified initial excitations, by screening the different possible relaxation channels. For each channel, the many-body Hamiltonian is mapped onto a respective all-vibrational Spin-Boson Hamiltonian, expressed in terms of the harmonic frequencies and the anharmonic coupling parameters obtained from the electronic structure of the molecule in its environment. A focus is given on the formulation of the relaxation rates when different limits of perturbation theory apply. In these cases the proposed Spin-Boson Screening approach becomes especially powerful.
The Journal of Chemical Physics, 2022
High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime... more High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime form polariton states by means of strong coupling to molecular vibrations. We studied polaritons formed by carbonyl stretching modes of (poly)methyl methacrylate on resonant antenna arrays using femtosecond 2DIR spectroscopy. At a normal incidence of excitation light, doubly degenerate antenna-lattice resonances (ALRs) form two polariton states: a lower polariton and an upper polariton. At an off-normal incidence geometry of 2DIR experiments, the ALR degeneracy is lifted and, consequently, the polariton energies are split. We spectrally resolved and tracked the time-dependent evolution of a cross-peak signal associated with the excitation of reservoir states and the unidirectional transfer of the excess energy to lower polaritons. Bi-exponential decay of the cross-peak suggests that a reversible energy exchange between the bright and dark lower polaritons occurs with a characteristic tr...
The Journal of Physical Chemistry C, 2022
Ultrafast studies of molecular dynamics using femtosecond twodimensional vibrational spectroscopy... more Ultrafast studies of molecular dynamics using femtosecond twodimensional vibrational spectroscopy (2DIR) provide unique insights on molecular interactions. Recently, such studies were extended from bulk samples to molecules on surfaces of noble metals, including disordered and engineered nanostructures. The metal nanostructures provide field enhancement allowing sensitive measurements at interfaces, but they also alter the molecular dynamics. 2DIR measurements at interfaces reveal correlations between vibrational transitions and rates of the vibrational relaxation, dephasing, spectral diffusion, and resonant energy transfer. At the surfaces, molecular dynamics and interaction with the environment can be modified by geometrical constrains associated with tethering, by the interaction between the molecule and the substrate, or by the enhanced near-fields associated with the metal. Interestingly, in many cases, these anticipated effects were found to be absent or fade away already at the microscopic distances away from the surface. Herein, we provide an overview of recent experimental studies in the field.
The Journal of Physical Chemistry B, 2021
A detailed understanding of the molecular structure in nanoparticle ligand capping layers is cruc... more A detailed understanding of the molecular structure in nanoparticle ligand capping layers is crucial for their efficient incorporation into modern scientific and technological applications. Peptide ligands render the nanoparticles as biocompatible materials. Glutathione, a γ-ECG tripeptide, self-assembles into aggregates on the surface of ligand-free silver nanoparticles through intermolecular hydrogen bonding and forms a few nanometer-thick shells. Two-dimensional nonlinear infrared (2DIR) spectroscopy suggests that aggregates adopt a conformation resembling the β-sheet secondary structure. The shell thickness was evaluated with localized surface plasmon resonance spectroscopy and X-ray photoelectron spectroscopy. The amount of glutathione on the surface was obtained with spectrophotometry of a thiol-reactive probe. Our results suggest that the shell consists of ∼15 stacked molecular layers. These values correspond to the inter-sheet distances, which are significantly shorter than those in amyloid fibrils with relatively bulky side chains, but are comparable to glycine-rich silk fibrils, where the side chains are compact. The tight packing of the glutathione layers can be facilitated by hydrogen-bonded carboxylic acid dimers of glycine and the intermolecular salt bridges between the zwitterionic γ-glutamyl groups. The structure of the glutathione aggregates was studied by 2DIR spectroscopy of the amide-I vibrational modes using 13C isotope labeling of the cysteine carbonyl. Isotope dilution experiments revealed the coupling of modes forming vibrational excitons along the cysteine chain. The coupling along the γ-glutamyl exciton chain was estimated from these values. The obtained coupling strengths are slightly lower than those of native β-sheets, yet they appear large enough to point onto an ordered conformation of the peptides within the aggregate. Analysis of the excitons' anharmonicities and the strength of the transition dipole moments generally is in agreement with these observations.
The Journal of Chemical Physics, 2020
Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the fore... more Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the forefront of fundamental chemical and physical research for several decades. Among the spectroscopic observables of the ultrafast dynamics is the pure dephasing of vibrationally excited molecules. Using third-order nonlinear vibrational spectroscopy, including polarization-selective transient grating measurements of vibrational lifetime and orientational diffusion as well as two-dimensional infrared spectroscopy, we determined different individual line shape components of hydroxyl stretching (νOH) excitations in a homologous series of chlorophenols and obtained the corresponding pure dephasing rates. The pure dephasing rates are correlated with vibrational anharmonicity of the νOH mode, which is tuned remotely from the hydroxyl site by changing the position of the chlorine substituents on the phenol ring. We found that in molecules where the hydroxyl group is in its free form, the pure depha...
The Journal of Physical Chemistry Letters, 2018
Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have... more Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have been demonstrated to enhance 2DIR signals by multiple orders of magnitude. We design doubly-degenerate in-plane plasmonic normal modes of the symmetric trimer gap-antenna, which have orthogonal dipole moments excited by light of the appropriate polarization, to
Chemical Reviews, 2018
Plasmonic molecules are small assemblies of nanosized metal particles. Interactions between the p... more Plasmonic molecules are small assemblies of nanosized metal particles. Interactions between the particles modify their optical properties and make them attractive for multiple applications in spectroscopy and sensing. In this review, we focus on basic properties rather than on applications. Plasmonic molecules can be created using either nanofabrication methods or self-assembly techniques in solution. The interaction of plasmonic molecules with light leads to excitations that are classified using the concept of normal modes. The simplest plasmonic molecule is a dimer of particles, and its lowest energy excitation takes the form of a symmetric dipolar mode. More complex excitations take place when a larger number of particles is involved. The gaps between particles in a plasmonic molecule form hotspots in which the electromagnetic field is concentrated. Introducing molecules into these hotspots is the basis of a vast spectrum of enhanced spectroscopies, from surface-enhanced Raman scattering to surface-enhanced fluorescence and others. We show in this review how these spectroscopic methods can be used to characterize the fields around plasmonic molecules. Furthermore, the strong fields can be used to drive new phenomena, from plasmon-induced chemical reactions to strong coupling of quantum emitters with the plasmonic fields. We systematically discuss these phenomena, introducing in each case the theoretical basis as well as recent experimental realizations.
Single Nanoparticles and Single Cells, 2014
Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2014
The simplest plasmonic molecule (PM) is a cluster of 2-3 metal particles. 2. PMs can be generated... more The simplest plasmonic molecule (PM) is a cluster of 2-3 metal particles. 2. PMs can be generated by solution chemistry or nanofabrication. 3. Electromagnetic hot spots intheir gaps enhance Raman scattering or fluorescence. 4. Symmetry of a PM affects its excitations, which can be classified by group theory. 5. PMs can serve as antennas, sensors or quantum cavities interacting with molecules.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
ABSTRACT We demonstrate a light-induced method to enhance, control, and tune two-photon-absorptio... more ABSTRACT We demonstrate a light-induced method to enhance, control, and tune two-photon-absorption in bulk CZT:V crystals. The technique is reversible in real-time, and enhancement scales linearly with control-beam intensity, reaching 2.5 times of the original values.
Physical Review A, 2007
Femtosecond coherent phase control of resonance mediated ͑2+1͒ three-photon absorption is studied... more Femtosecond coherent phase control of resonance mediated ͑2+1͒ three-photon absorption is studied both theoretically and experimentally. The regime is perturbative of third order. The photoexcitation coherently combines elements of both nonresonant and resonance-mediated multiphoton transitions. By proper simple pulse shaping the three-photon absorption in Na is effectively controlled experimentally, enhanced up to ϳ300% of the absorption induced by the transform-limited pulse. It is achieved by phase manipulating intraand intergroup interferences involving two groups of three-photon excitation pathways: ͑i͒ on resonance and ͑ii͒ near resonance with the intermediate resonance state accessed by nonresonant two-photon transition.
The Journal of Physical Chemistry C, 2011
Gold island films displaying localized plasmon properties were prepared by evaporation of just-pe... more Gold island films displaying localized plasmon properties were prepared by evaporation of just-percolated Au films onto glass substrates followed by annealing at g550°C. Annealing induces depercolation and formation of large, singlecrystalline, well-separated islands, partially embedded in the glass. Two dewetting mechanisms were identified, depending on the initial film morphology. The variability of island sizes and shapes provides effective means of tuning the position of the localized surface plasmon resonance (LSPR) band in a wide wavelength range. With an increase in the Au nominal thickness a transition occurs from transducers dominated by absorbance to ones dominated by scattering. Numerical simulations taking into account the shape and size distribution in actual island samples are in agreement with the experimental spectra. Refractive index sensitivity (RIS) measurements at a constant wavelength or at a constant extinction, tailored to the specific transducer, provide superior sensitivity to refractive index change, up to ca. 600 nm RIU À1 in wavelength shift.
Nano Letters, 2013
We show that a hybrid system built of a plasmonic nanoparticle cluster and a single molecule can ... more We show that a hybrid system built of a plasmonic nanoparticle cluster and a single molecule can attain maximal Raman optical activity (ROA), converting linearly polarized light into purely circularly polarized light at the Raman-scattered frequency. In contrast to standard molecular ROA, the effect described here does not involve magnetic modes and is attributed to off-resonance excitation of electric-dipole plasmon modes of the nanoparticle cluster. A model based on a combination of harmonic oscillators excited at the frequency of the Raman-scattered light is shown to successfully capture the physics of the effect.
The Journal of Physical Chemistry Letters, 2013
Coherent dynamics of degenerate quantum states symmetry-broken on the femtosecond timescale is fo... more Coherent dynamics of degenerate quantum states symmetry-broken on the femtosecond timescale is found to exhibit the phenomenon of quantum beats. Frequency-resolved and polarizationselective heterodyned transient grating spectroscopy enabled us to retrieve the oscillation pattern characteristic of the beating in systems undergoing ultrafast dynamical processes. This methodology applies to the general phenomena of coherence dynamics which is important in any ultrafast multidimensional spectroscopy. A particular application to the vibrational spectroscopy of coherence in the degenerate normal modes of the tricyanomethanide anion solvated in water is explored in this study. The relaxation of the cross-polarization transient grating anisotropy is shown to reflect the loss of the vibrational coherence, which is caused by ultrafast dynamics of the water solvation shell.
The Journal of Chemical Physics, 2013
Molecular ions undergoing ultrafast conformational changes on the same time scale of water motion... more Molecular ions undergoing ultrafast conformational changes on the same time scale of water motions are of significant importance in condensed phase dynamics. However, the characterization of systems with fast molecular motions has proven to be both experimentally and theoretically challenging. Here, we report the vibrational dynamics of the non-degenerate (C12,C13)-oxalate anion, an ultrafast rotor, in aqueous solution. The infrared absorption spectrum of the (C12,C13)-oxalate ion in solution reveals two vibrational transitions separated by approximately 40 cm−1 in the 1500–1600 cm−1 region. These two transitions are assigned to vibrational modes mainly localized in each of the carboxylate asymmetric stretch of the ion. Two-dimensional infrared spectra reveal the presence and growth of cross-peaks between these two transitions which are indicative of coupling and population transfer, respectively. A characteristic time of sub-picosecond cross-peaks growth is observed. Ultrafast pump...