Resonance Raman Transition Research Articles

Influence of varying thermodynamic parameters on the structural behavior of nano-crystalline europium sesquioxide

The present manuscript reports structural evolutions in nano-crystalline europium sesquioxide (Eu2O3) with increasing pressure up to 22 GPa at ambient temperature and at a varying temperature in the range from 80 to 440 K. The sample was characterized at ambient and was found to be cubic in structure with nano-size using various characterization routes. External pressure was applied on the sample using the diamond anvil cell (DAC) up to about 22 GPa and the ensuing changes were investigated using Raman spectroscopy. The material showed a structural phase transition from cubic to the hexagonal phase which was initiated around 4.79 GPa and completed around 15 GPa. The material exhibited this hexagonal phase up to the highest pressure of 22 GPa. From the pressure dependent phonon mode variation, the mode Grüneisen parameters were estimated and reported for the first time. For the most prominent Fg mode for the present sample, the mode Grüneisen parameter was found to be 1.36. The temperature dependent study on the cubic sample, revealed the stability of the material up to 440 K with new bands developing towards higher wavenumbers. These new bands might be a result of the resonant Raman transitions of the cubic phase. Further, the temperature dependent shifts were used to deduce the anharmonic constants which showed the softening of the phonon modes and the dominance of three-phonon decay process.

Multidimensional Spectral Fingerprints of a New Family of Coherent Analytical Spectroscopies.

Triply resonant sum frequency (TRSF) and doubly vibrationally enhanced (DOVE) spectroscopies are examples of a recently developed family of coherent multidimensional spectroscopies (CMDS) that are analogous to multidimensional NMR and current analytical spectroscopies. CMDS methods are particularly promising for analytical applications because their inherent selectivity makes them applicable to complex samples. Like NMR, they are based on creating quantum mechanical superposition states that are fully coherent and lack intermediate quantum state populations that cause quenching or other relaxation effects. Instead of the nuclear spin states of NMR, their multidimensional spectral fingerprints result from creating quantum mechanical mixtures of vibrational and electronic states. Vibrational states provide spectral selectivity, and electronic states provide large signal enhancements. This paper presents the first electronically resonant DOVE spectra and demonstrates the capabilities for analytical chemistry applications by comparing electronically resonant TRSF and DOVE spectra with each other and with infrared absorption and resonance Raman spectra using a Styryl 9 M dye as a model system. The methods each use two infrared absorption transitions and a resonant Raman transition to create a coherent output beam, but they differ in how they access the vibrational and electronic states and the frequency of their output signal. Just as FTIR, UV-vis, Raman, and resonance Raman are complementary methods, TRSF and DOVE methods are complementary to coherent Raman methods such as coherent anti-Stokes Raman spectroscopy (CARS).

Ultrafast population transfer to excited valence levels of a molecule driven by x-ray pulses

First-principles quantum-mechanical calculations of an intense-field ultrafast two-color core-hole stimulated Raman process in nitric oxide are presented. They employ the multiconfiguration time-dependent Hartree-Fock (MCTDHF) method with all 15 electrons active. These calculations demonstrate a robust excitation localized on an atom through a core-electron stimulated Raman transition, the first step in proposed stimulated x-ray Raman spectroscopy experiments. A total population transfer of approximately 41% into valence excited states and 30% ionization is obtained via two concurrent 1.31-fs pulses with maximum intensities of 0.5 and $3\ifmmode\times\else\texttimes\fi{}{10}^{17}\text{W}{\mathrm{cm}}^{\ensuremath{-}2}$. It is found that both resonant and nonresonant (via the continuum) Raman transitions contribute. All aspects of these calculations except for ac Stark shifts are converged with a modest basis of 11 orbitals, demonstrating the efficiency of MCTDHF for the treatment of nonperturbative electronic dynamics in molecules.

Resonance IR: A Coherent Multidimensional Analogue of Resonance Raman

This work demonstrates the use of triply resonant sum frequency (TRSF) spectroscopy as a "resonance IR" analogue to resonance Raman spectroscopy. TRSF is a four-wave-mixing process where three lasers with independent frequencies interact coherently with a sample to generate an output at their triple summation frequency. The first two lasers are in the infrared and result in two vibrational excitations, while the third laser is visible and induces a two-quantum anti-Stokes resonance Raman transition. The signal intensity grows when the laser frequencies are all in resonance with coupled vibrational and electronic states. The method therefore provides electronic enhancement of IR-active vibrational modes. These modes may be buried beneath solvent in the IR spectrum and also be Raman-inactive and therefore inaccessible by other techniques. The method is presented on the centrosymmetric complex copper phthalocyanine tetrasulfonate. In this study, the two vibrational frequencies were scanned across ring-breathing modes, while the visible frequency was left in resonance with the copper phthalocyanine tetrasulfonate Q band, resulting in a two-dimensional infrared plot that also reveals coupling between vibrational states. TRSF has the potential to be a very useful probe of structurally similar biological motifs such as hemes, as well as synthetic transition-metal complexes.

Cavity-QED simulation of qubit-oscillator dynamics in the ultrastrong-coupling regime

We propose a quantum simulation of a two-level atom coupled to a single mode of the electromagnetic field in the ultrastrong-coupling regime based upon resonant Raman transitions in an atom interacting with a high finesse optical cavity mode. We show by numerical simulation the possibility of realizing the scheme with a single rubidium atom, in which two hyperfine ground states make up the effective two-level system, and for cavity QED parameters that should be achievable with, for example, microtoroidal whispering-gallery-mode resonators. Our system also enables simulation of a generalized model in which a nonlinear coupling between the atomic inversion and the cavity photon number occurs on an equal footing with the (ultrastrong) dipole coupling and can give rise to critical-type behavior even at the single-atom level. Our model takes account of dissipation, and we pay particular attention to observables that would be readily observable in the output from the system.

Spin-orbit interaction induced singlet-triplet resonant Raman transitions in quantum dot helium

From our theoretical studies of resonant Raman transitions in two-electron quantum dots (artificial helium atoms) we show that in this system, the singlet-triplet Raman transitions are allowed (in polarized configuration) only in the presence of spin-orbit interactions. With an increase of the applied magnetic field this transition dominates over the singlet-singlet and triplet-triplet transitions. This intriguing effect can therefore be utilized to tune Raman transitions as well as the spin-orbit coupling in few-electron quantum dots.

Time- and frequency-domain polariton interference

We present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple Λ transitions driving a single-spin coherence. Our scheme can behave as a controllable time-delayed beamsplitter with dynamically tuneable splitting ratio and allows, in principle, for unity interference visibility.

Resonant Raman Transitions into Singlet and Triplet States in InGaAs Quantum Dots Containing Two Electrons

Semiconductor quantum dots containing two electrons, also called artificial quantum-dot helium atoms, are model structures to investigate the most fundamental many-particle states induced by Coulomb interaction and the Pauli exclusion principle. Here, electronic excitations in quantum-dot helium are investigated by resonant Raman spectroscopy in magnetic fields. We observe transitions from the ground state into the excited singlet state and, in the depolarized Raman configuration which allows spin-flip processes, into the triplet state.

Impulsive stimulated Raman transition on theBstate of iodine molecules via repulsive states

Impulsive Raman transition on the $B\text{ }^{3}\ensuremath{\Pi}({0}_{u}^{+})$ state of the iodine molecule is reported. Several rovibrational states in the $B$ state are populated with the second harmonics of a neodymium-doped yttrium lithium fluoride (Nd:YLF) laser ($\ensuremath{\le}250\text{ }\text{ns}$, 527 nm). The population alteration with $\ensuremath{\Delta}v=\ifmmode\pm\else\textpm\fi{}1$ and $\ifmmode\pm\else\textpm\fi{}2$ are induced with a Ti:sapphire laser ($\ensuremath{\sim}30\text{ }\text{fs}$, 780 nm, ${10}^{12}--{10}^{14}\text{ }\text{W}/{\text{cm}}^{2}$) and detected by the $B\text{\ensuremath{-}}X$ dispersed fluorescence spectrum. The alteration is attributed to the Raman transition on the basis of the spectral profile, the pressure dependence, and the laser power dependence. The observed Raman transition is concluded to be a continuum resonance Raman transition mediated by upper repulsive states. Competing dissociation and ionization processes are also discussed by analyzing the laser power dependence.

Manipulation of ro-vibronic wave packet composition using chirped ultrafast laser pulses

Linearly chirped femtosecond laser pulses are used to excite ro-vibrational wave packets in lithium dimers from a single well-prepared launch state. Two-photon resonant Raman transitions excite a manifold of rotational states in a coherent superposition. Excitation with positively chirped laser pulses is shown to enhance a quantum beat involving states with lower rotational quantum numbers, whereas negatively chirped pulses enhance a quantum beat between states with higher rotational quantum numbers, thus steering the rotational coherences to higher or lower rotational states. Time-dependent perturbation theory calculations verify the magnitudes and directions of the enhancement as a function of the applied chirp. The quantitative calculations and experimental results demonstrate that excitation with chirped pulses is an effective method for enhancing specific rotational coherences involving higher or lower rotational states.

Vacuum Rabi splitting and intracavity dark state in a cavity-atom system

We report experimental measurements of the transmission spectrum of an optical cavity coupled with cold Rb atoms. We observe the multiatom vacuum Rabi splitting of a composite cavity and atom system. When a coupling field is applied to the atoms and induces the resonant two-photon Raman transition with the cavity field in a $\ensuremath{\Lambda}$-type system, we observe a cavity transmission spectrum with two vacuum Rabi sidebands and a central peak representing the intracavity dark state. The central peak linewidth is significantly narrowed by the dark-state resonance and its position is insensitive to the frequency change of the empty cavity.

Two Stereoisomers of Spheroidene in the Rhodobacter sphaeroides R26 Reaction Center: A DFT Analysis of Resonance Raman Spectra

From a theoretical analysis of the resonance Raman spectra of 19 isotopomers of spheroidene reconstituted into the reaction center (RC) of Rhodobacter sphaeroides R26, we conclude that the carotenoid in the RC occurs in two configurations. The normal mode underlying the resonance Raman transition at 1239 cm −1, characteristic for spheroidene in the RC, has been identified and found to uniquely refer to the cis nature of the 15,15′ carbon-carbon double bond. Detailed analysis of the isotope-induced shifts of transitions in the 1500–1550 cm −1 region proves that, besides the 15,15′- cis configuration, spheroidene in the RC adopts another cis-configuration, most likely the 13,14- cis configuration.

KLL Auger resonant Raman transition in metallic Cu and Ni

High energy resolution KL 23L 23 Auger spectra of polycrystalline Cu and Ni were measured using photon energies up to about 50 eV above the K-absorption edge and down to 5 eV (Cu KLL) and 4 eV (Ni KLL) below threshold. The spectra show strong satellite structures varying considerably as a function of the photon energy. In the sub-threshold region the linear dispersion of the diagram line energy positions and a distortion of the line shape as a function of photon energy, attributable to the Auger resonant Raman process, is clearly observed, indicating the one-step nature of the Auger emission. These changes in the resonant spectra are interpreted using a simple model based on resonant scattering theory in combination with partial density of states obtained from cluster molecular orbital (DV- Xα) calculations.

Coherent control through near-resonant Raman transitions

The phase of an electronic wave function is shown to play an important role in coherent control experiments. By using a pulse shaping system with a femtosecond laser, we explore the phase relationships among resonant and off-resonant Raman transitions in Li{sub 2} by measuring the phases of the resulting wave packets, or quantum beats. Specific pixels in a liquid-crystal spatial light modulator are used to isolate the resonant and off-resonant portions of the Raman transitions in Li{sub 2}. The off-resonant Raman transitions have an approximately 90 degree sign phase shift with respect to the resonant Raman transition, and there is an approximately 180 degree sign phase shift between the blue-detuned and the red-detuned off-resonant Raman transitions. Calculations using second-order time-dependent perturbation theory for the electronic transitions agree with the experimental results for the laser pulse intensities used here. Interferences between the off-resonant Raman transitions as a function of detuning are used to demonstrate coherent control of the Raman quantum wave packet.

Imaging wavepacket interferences using Auger resonant Raman spectroscopy

Novel interference effects are observed in the Auger resonant Raman transitions of core-excited HF. Pronounced oscillations, controlled by detuning above the resonance maximum, appear in the spectator decay spectra of the dissociating molecule. Using predictions from the time-dependent theory of the resonant inelastic Raman scattering, these observations are explained by a favorable spatial localization of the nuclear wavepacket in the intermediate state during its creation. This phenomenon should occur whenever photoexcitation, electronic decay and nuclear dynamics have comparable time scales.

Photoluminescence in small isotactic, atactic and syndiotactic PVA polymer molecules in water

Polyvinyl alcohol (PVA) dispersed in small polymer molecules in water (∼4.0 g/dl) has photoluminescence (PL) in three distinct bands at 415, 437, and 465 nm. This occurs in a resonance excitation with vibronic level of O–H stretching vibration ν 1 (or overtone) at λ ex =400 or 350 nm wavelength of excitation. Relative band intensities, which lie in the 100:94:45 order in three bands in λ ex =350 nm excitation, vary depending on the excitation process with a function of the value of λ ex and PVA concentration in the solution. A single band occurs of the absorption spectrum at 196 nm in an altogether different π←π* electronic transition. The three PL bands thus attribute to n←π* electronic transition in non-bonding 2p 2 (O) electrons in free OH groups in three syndiotactic (s), atactic (a), and isotactic (i) conformers of PVA polymer molecules. ν 1 band appears in a resonance Raman transition at ∼3215, 3475, or 3560 cm −1 in the respective conformers. Solvent interaction with H 2 O molecules (destabilizes s- and i-PVA to convert into a-PVA) quenches the PL progressively in dilute solutions so that it no longer occurs in concentrations below 1.0 g/dl. The results are analyzed and modeled in terms of the localized n -electrons in small polymer molecules.

Characterization of the pH-dependent resonance Raman transitions of archaeal and bacterial Rieske [2Fe-2S] proteins.

The pH-dependent resonance Raman (RR) spectral changes of the cytochrome bc1-associated, high-potential Rieske proteins have frequently been invoked to explain the redox-linked ionization behavior. We report herein RR spectral data of archaeal and bacterial Rieske proteins that directly demonstrate the pH-dependent changes near and above pKa,ox2, but not around pKa,ox1, of the visible circular dichroism (CD) transitions. The RR spectral changes are attributed to modification of the immediate [2Fe-2S] cluster environment due to deprotonation of some exchangeable amide groups in the polypeptide backbone, rather than previously assumed simple changes of the Fe-Nimid stretching vibrations.

Strong-field molecular alignment for quantum logic and quantum control

We discuss an approach to quantum control based on initial adiabatic tuning of the field-free Hamiltonian by a strong laser field to optimize the system for the desired transitions induced by the control laser pulse. As an illustration, we describe single-qubit, two-qubit, and some qudit logical gates within rotational and vibrational states of a diatomic molecule. Gate operations use resonant Raman transitions, and the prior adjustment of the Hamiltonian is done by a strong nonresonant aligning field.

Doppler three-level (V-scheme) laser without population inversion

The theory of amplification and lasing without population inversion in a three-level medium with inhomogeneous broadening via the formation of an open V configuration is elaborated. The conditions for energy transfer from the infrared into the visible spectral range, i.e., the conditions of up-conversion nb>nc>na, and the external field required for saturation of the b⇄a transition are established. Two-photon resonant Raman transitions in ensemble of mobile atoms of a gas-discharge plasma are analyzed. The frequency shift of the probe field spectrum as a whole is shown to be governed by the frequency shift of the pump field multiplied by the ratio of the wave numbers of the probe amplification field and the pump field. The interaction of atoms through Ne transitions with the pump field (λ=1.15 em, 2p4-2s2 transition) and the lasing field (λ=0.6328 em, 3s2-2p2 transition) with an increase in the lasing frequency by a factor of 1.82 with respect to the absorbed radiation is calculated.

Resonance Raman Spectroscopy of Mass Selected Chromium Trimers in an Argon Matrix

The resonance Raman spectra of mass-selected chromium trimers (Cr3) in argon matrixes have been obtained. Five resonance Raman transitions were observed between 450 and 690 nm. Four of them are assigned to a totally symmetric (a1‘) vibrational progression, from which we obtain a ground-state harmonic frequency of ωe = 432.2 cm-1 with ωexe = 16.3 cm-1. The other Raman line, observed at 302.0 cm-1, is assigned to the degenerate bending motion v2(e‘) of the triatomic metal cluster. The geometry of the ground state is that of an equilateral triangle (D3h). These results provide a value of the stretching force constant of ke = 1.91 mdyne/A and a spectroscopic atomization energy of 0.36 eV.