Frequency Upshift Research Articles

Photoreduction of carotenoids in the aerobic anoxygenic photoheterotrophs probed by real time Raman spectroscopy

The Aerobic anoxygenic phototrophic bacteria (AAPB) Roseobacter denitrificans and Roseobacter litoralis are widespread in the bacterioplankton community with a particular role in the marine carbon cycle. Measurements of carotenoids isolated from dark-grown cells indicated the presence of spheroidenone (SO, N = 11) and of 3,4 dihydrospheroidenone (N = 10) in the carotenoids isolated from illuminated cells. Time-dependent Raman 514 nm excitation experiments of R. denitrificans and R. litoralis cells grown under illumination demonstrated that v1 (C=C) of SO exhibits a time-dependent substantial frequency upshift relative to its frequency in the dark-grown cells, in a manner resembling shorting the conjugation length (N). We suggest that the irreversible dark-SO to light- 3,4 dihydrospheroidenone transition observed in the intact carotenoids of R. denitrificans and R. litoralis cells is an operative photoreduction strategy of SO containing AAPB that affects the energy transfer mechanism.

Erratum to "Looking for Mickey Mouse™ But Finding a Munchkin: The Perceptual Effects of Frequency Upshifts for Single-Sided Deaf, Cochlear Implant Patients".

[Figure: see text].

Frequency Upshift of the Transverse Optical Phonon Resonance in GaAs by Femtosecond Electron-Hole Excitation.

The impact of transient electric currents on the transverse optical (TO) phonon resonance is studied after excitation by two femtosecond near-infrared pulses via the fourth-order nonlinear terahertz emission. Nonlinear signals due to interband shift currents and heavy-hole-light-hole polarizations are separated from Raman-induced TO phonon coherences. The latter display a frequency upshift by some 100GHz upon interband excitation of an electron-hole plasma. The frequency shift is caused by transverse electronic shift currents, which modify the dielectric function. A local-field model based on microscopic current densities reproduces the observed frequency upshift.

Influence of flying mirror features and time delay between two counterpropagating laser pulses on the generated attosecond pulse intensity in near-critical density plasmas

The attosecond pulse generation by the interaction of two counterpropagating ultrashort laser pulses with near-critical density plasma is simulated using two-dimensional particle in the cell method. Results of the simulations showed the flying mirror properties such as density and shape change, while moving through the plasma, behind the intense driver laser. We investigated the effects of the mirror features on the produced attosecond pulse intensity by setting various delay times between the driver and source pulses so that the source encounters the mirror at different points. It is demonstrated that the higher density of the mirror, particularly in its center (due to the Gaussian transverse profile of the source), in addition to its suitable curvature and surface smoothness, results in a more intense reflection. Moreover, a considerable size of the hole created in the mirror center due to the self-injection process has a destructive effect on the reflection efficiency. Finally, an efficient reflection can be obtained by controlling the delay time. The optimal delay for arbitrary parameters of the laser and plasma depends on the region in which the most efficient flying mirrors are created by the mutual interaction of the plasma density and the driver amplitude along with considering the pulse situation when reaching the mirror. By analyzing the electron phase space, it was found that the velocity of density spikes changes rapidly when passing through the plasma. The higher speed of the electrons of the mirrors contributing to the source reflection leads to the production of the higher upshifted frequency peak in different source delays.

Recoil effects on reflection from relativistic mirrors in laser plasmas

Relativistic mirrors can be realized with strongly nonlinear Langmuir waves excited by intense laser pulses in underdense plasma. On reflection from the relativistic mirror, the incident light affects the mirror motion. The corresponding recoil effects are investigated analytically and using particle-in-cell simulations. It is found that if the fluence of the incident electromagnetic wave exceeds a certain threshold, the relativistic mirror undergoes a significant back reaction and splits into multiple electron layers. The reflection coefficient of the relativistic mirror and the factors of electric field amplification and frequency upshift of the electromagnetic wave are obtained.

Time-Resolved Femtosecond Stimulated Raman Spectra and DFT Anharmonic Vibrational Analysis of an Electronically Excited Rhenium Photosensitizer.

Time-resolved femtosecond stimulated Raman spectra (FSRS) of a prototypical organometallic photosensitizer/photocatalyst ReCl(CO)3(2,2'-bipyridine) were measured in a broad spectral range ∼40-2000 (4000) cm-1 at time delays from 40 fs to 4 ns after 400 nm excitation of the lowest allowed electronic transition. Theoretical ground- and excited-state Raman spectra were obtained by anharmonic vibrational analysis using second-order vibrational perturbation theory on vibrations calculated by harmonic approximation at density functional theory-optimized structures. A good match with anharmonically calculated vibrational frequencies allowed for assigning experimental Raman features to particular vibrations. Observed frequency shifts upon excitation (ν(ReCl) and ν(CC inter-ring) vibrations upward; ν(CC, CN) and ν(Re-C) downward) are consistent with the bonding/antibonding characters of the highest occupied molecular orbital and the lowest unoccupied molecular orbital involved in excitation and support the delocalized formulation of the lowest triplet state as ReCl(CO)3 → bpy charge transfer. FSRS spectra show a mode-specific temporal evolution, providing insights into the intersystem crossing (ISC) mechanism and subsequent relaxation. Most of the Raman features are present at ∼40 fs and exhibit small shifts and intensity changes with time. The 1450-1600 cm-1 group of bands due to CC, CN, and CC(inter-ring) stretching vibrations undergoes extensive restructuring between 40 and ∼150 fs, followed by frequency upshifts and a biexponential (0.38, 21 ps) area growth, indicating progressing charge separation in the course of the formation and relaxation of the lowest triplet state. Early (40-150 fs) restructuring was also observed in the low-frequency range for ν(Re-Cl) and δ(Re-C-O) vibrations that are presumably activated by ISC. FSRS experimental innovations employed to measure low- and high-energy Raman features simultaneously are described and discussed in detail.

Study of a 0.35 THz Extended Interaction Oscillator Driven by a Pseudospark-Sourced Sheet Electron Beam

A compact high-power extended interaction oscillator (EIO) driven by a pseudospark-sourced (PS-sourced) sheet electron beam (SEB) is presented at 0.35 THz. It combines the advantages of a planar interaction circuit and a SEB generated from the PS discharge, including a large beam cross-section, high gain per unit length, and high current density with the additional benefit of not requiring an external focusing magnetic field. Staying within what is achievable with microfabrication techniques, the influence of tolerance on the Q value, resonance frequency, and characteristic impedance was investigated. The effect of surface roughness caused by the manufacturing method on Ohmic loss of the material surface was studied. The advanced microfabrication techniques of Ultra Violet Lithographie, Galvanik, and Abformung (UV-LIGA) and Nano-computer numerical control (Nano-CNC), which are capable of realizing high precision and a metal surface of sufficient smoothness, were proposed to manufacture the planar structures. The effect of plasma density in PS-sourced SEB on the resonance frequency of the EIO circuit was investigated. The simulation results showed that the output signal had a slight frequency upshift and a decrease of the output power as the plasma density increased at 0.35 THz, which is consistent with the theoretical analysis. Beam–wave interaction simulations for this planar EIO predicted a peak output power of 1.8 kW at ~0.35 THz using an effective value of conductivity of ${1.1} \times {10}^{{7}}$ S/m to take into account the skin depth and surface roughness.

Tracking Photoinduced Au-Au Bond Formation through Transient Terahertz Vibrations Observed by Femtosecond Time-Domain Raman Spectroscopy.

Real-time observation of chemical bond formation and subsequent nuclear rearrangements is an ultimate goal of chemical science. Yet, such attempts have been hampered by the technical difficulty of triggering bond formation at well-defined, desired timing. The trimer of dicyanoaurate complex ([Au(CN)2-]3) is an ideal system for achieving this aim because the tight covalent Au-Au bonds are formed upon photoexcitation. Despite the apparent simplicity of the system, however, recent time-resolved studies failed to construct a consistent picture of its ultrafast dynamics. Here, we report femtosecond time-domain Raman tracking of ultrafast structural dynamics of the [Au(CN)2-] trimer upon photoinduced Au-Au bond formation. The obtained Raman data reveal that the Au-Au breathing vibration at ∼90 cm-1 exhibits a gradual frequency upshift in a few picoseconds, demonstrating a continuous bent-to-linear structural change on the triplet-state potential energy surface upon the Au-Au bond formation. The comprehensive ultrafast spectroscopic study settles the controversy on this prototypical molecular assembly.

On the Propagation of a Circularly Polarized Electromagnetic Wave Through a Temporal Interface Between Air and a Magneto Plasma

It is shown that a right-hand/left-hand circularly polarized wave propagating along the magnetic field is converted to three waves by a suddenly created plasma. The right-hand circularly polarized wave is converted to two forward (R-mode and slow R-mode of the magnetoplasma) and one backward (L-mode) propagating waves; and in the left-hand circular polarization case, the wave is converted to one forward (L-mode) and two backward (R-mode and slow R-mode) propagating waves. As the background magnetic field approaches zero, the slow R-mode converts to a wiggler magnetic field, which is found in the unmagnetized case. Conservation of wave energy and power flux in the mode conversion is verified. Using the Abraham expression as the relationship between the momentum and energy of a photon in a dielectric medium, conservation of momentum in the mode conversion is also demonstrated. When a strong magnetic field is embedded in the background, a suddenly created low-density plasma can achieve a large frequency upshift on a right-hand circularly polarized wave.

Attosecond pulse generation by relativistic flying mirrors in laser-plasma interaction: Effect of plasma density and driver amplitude on the generated pulse

The generation of high-intensity attosecond pulses by the interaction of two counterpropagating short laser pulses with underdense plasma is investigated. By using parallel fully kinetic particles in cell simulation, which shows the formation of relativistic flying mirrors in the wake wave of the intense driver laser pulse and the focusing reflection of the weak source pulse, it is demonstrated that intense attosecond pulses can be produced under the optimized conditions of plasma density and driver laser amplitude according to the relativistic similarity theory. In addition, it is shown that the frequency of the source pulse is upshifted by a factor from 10 to 80 corresponding to a reflected radiation wavelength from 20 to 164 nm which lies in the extreme ultraviolet region, while most of the energy lies around a frequency upshift of 20, in agreement with the measured Lorentz factor. The intensity of the main attosecond pulse is two orders higher than the source pulse intensity.

Looking for Mickey Mouse™ But Finding a Munchkin: The Perceptual Effects of Frequency Upshifts for Single-Sided Deaf, Cochlear Implant Patients.

Purpose Our aim was to make audible for normal-hearing listeners the Mickey Mouse™ sound quality of cochlear implants (CIs) often found following device activation. Method The listeners were 3 single-sided deaf patients fit with a CI and who had 6 months or less of CI experience. Computed tomography imaging established the location of each electrode contact in the cochlea and allowed an estimate of the place frequency of the tissue nearest each electrode. For the most apical electrodes, this estimate ranged from 650 to 780 Hz. To determine CI sound quality, a clean signal (a sentence) was presented to the CI ear via a direct connect cable and candidate, and CI-like signals were presented to the ear with normal hearing via an insert receiver. The listeners rated the similarity of the candidate signals to the sound of the CI on a 1- to 10-point scale, with 10 being a complete match. Results To make the match to CI sound quality, all 3 patients need an upshift in formant frequencies (300-800 Hz) and a metallic sound quality. Two of the 3 patients also needed an upshift in voice pitch (10-80 Hz) and a muffling of sound quality. Similarity scores ranged from 8 to 9.7. Conclusion The formant frequency upshifts, fundamental frequency upshifts, and metallic sound quality experienced by the listeners can be linked to the relatively basal locations of the electrode contacts and short duration experience with their devices. The perceptual consequence was not the voice quality of Mickey Mouse™ but rather that of Munchkins in The Wizard of Oz for whom both formant frequencies and voice pitch were upshifted. Supplemental Material https://doi.org/10.23641/asha.9341651.

Proton-Coupled Electron Transfer of Plastoquinone Redox Reactions in Photosystem II: A Pump–Probe Ultraviolet Resonance Raman Study

Plastoquinones (PQs) act as electron and proton mediators in photosystem II (PSII) for solar-to-chemical energy conversion. It is known that the redox potential of PQ varies in a wide range spanning hundreds of millivolts; however, its structural origin is not known yet. Here, by developing a pump-probe ultraviolet resonance Raman technique, we measured the vibrational structures of PQs including QA and QB in cyanobacterial PSII directly. The conversion of QA to QA•- in the Mn-depleted PSII is verified by direct observation of the distinct QA•- vibrational bands. A frequency upshift of the ring C=O/C=C stretch band at 1565 cm-1 for QA•- was observed, which suggests a π-π interaction between the quinone ring and Trp253. In contrast, proton-coupled reduction of QA to QAH upon light-driven electron transfer is demonstrated in PSII without QB bound. The H-bond between QA and His214 is likely the proton origin of this proton-coupled electron transfer.

Are we ready to transfer optical light to gamma-rays?

Scattering relativistic electrons with optical lasers can result in a significant frequency upshift of photons, potentially producing γ-rays. This is what linear Compton scattering taught us. Ultra-intense lasers offer nowadays a new paradigm where multiphoton absorption effects come into play. These effects can result in higher harmonics, higher yields, and also electron-positron pairs. This article intends to discriminate the different laser scenarios that have been proposed over the past few years as well as to give scaling laws for future experiments. The energy conversion from lasers or particles to high-frequency photons is addressed for both the well-known counter propagating electron beam-laser interaction and quantum-electrodynamics cascades triggered by various lasers. Constructing bright and energetic gamma-ray sources in controlled conditions is within an ace of seeing the light of day.

Shift down, look up: A test of the non‐linearity and fear hypothesis in a non‐vocal skink

AbstractThe non‐linearity and fear hypothesis predicts that certain non‐linear sounds are one way to evoke antipredator responses in both birds and mammals. This hypothesis, however, has not been studied in non‐vocal species or in reptiles. Such a study would be important because if non‐linear sounds are evocative even in a species that does not produce sounds, then there may be generally salient cues of risk in these sounds. We asked whether non‐vocal lizards, white‐bellied copper‐striped skinks (Emoia cyanura), respond to experimentally broadcast non‐linearities. This species is ideal to ask the question in because prior research has shown that they respond to predator sounds and alarm calls of other species even though they are not vocal. We conducted playback experiments with three computer‐generated simulated non‐linearities to assess whether or not skinks increased antipredator behavior after hearing them. We controlled for novelty by broadcasting a 3‐kHz, 500‐ms pure tone and tropical kingbird (Tyrannus melancholicus) song. Our treatments consisted of a 3‐kHz, 400‐ms pure tone followed by a frequency shift up to 5‐kHz for 100‐ms, a 3‐kHz, 400‐ms pure tone to frequency shift down to 1‐kHz for 100‐ms, and a pure tone followed by 100‐ms of white noise. Following a total of 222 playbacks, we categorized responses into looking, locomotion, and high locomotion, focusing on how skinks changed their rates of time allocation from baseline. We examined 95% confidence intervals to identify whether skinks responded to playbacks and fitted general linear models followed by pairwise comparisons to ask whether skinks discriminated between broadcast stimuli. We found that skinks were especially responsive to frequency downshifts: They significantly increased looking and locomotion, consistent with our predictions based on the non‐linearity and fear hypothesis. Surprisingly, they decreased rates of looking behavior after hearing frequency upshifts, possibly suggesting an increase in relaxed behavior. While skinks responded to noise by increasing their rate of locomotion, this response was not significantly different from controls. We conclude that skinks increase antipredator behavior after hearing downshifts more than any other type of non‐linearity. This provides some support for the non‐linearity and fear hypothesis; even non‐vocal species may respond fearfully to specific types of non‐linear sounds.

Modeling protic dicationic ionic liquids based on quaternary ammonium, imidazolium or pyrrolidinium cations and bis(trifluoromethanesulfonyl)imide anion: Structure and spectral characteristics

Protic dicationic ionic liquids (PDILs) have attracted growing attention owing to their applications in domains of electrochemistry, proton conducting materials and other diverse areas. In the present work protic dicationic ionic liquids (PDILs) comprising of quaternary ammonium-, imidazolium- or pyrrolidinium-dications and bis(trifluoromethanesulfonyl)imide (Tf2N‾) anion have been modelled as the dication-(Tf2N)2 complexes. Electronic structure, vibrational and 1H NMR spectra of these complexes have been derived employing the M06-2x density functional theory. Theoretical calculations have shown that the strength of cation-anion binding follows the order: methylpyrrolidinum > quaternary ammonium > butylpyrrolidinium > imidazolium, which can be attributed to number and strength of N-H---O and C-H---O interactions. The dication-(Tf2N)2 complexes emerge with signature in frequency up-shift of the characteristic N-H stretching in their infrared spectra. Underlying molecular interactions are unveiled through natural bond orbital analyses, Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction reduced density gradient method. The calculations have shown that cation-anion binding energies increase linearly with kinetic energy density component G(r) in QTAIM analysis and proton affinities in the PDILs. A correlation between change in free energies accompanying the dication-(Tf2N)2 complexes and proton affinities has also been established.

Frequency up-shift in the stimulated thermal scattering under two-photon absorption in liquids and colloids of metal nanoparticles

We report the results of the experimental and theoretical study of stimulated temperature scattering in toluene and hexane solutions of Ag-nanoparticles, as well as in pure toluene in the two-photon absorption regime. A four-wave mixing scheme with two counter-propagating pump waves of the same frequency is utilised to demonstrate the lasing effect and the amplification of the backscattered anti-Stokes signal. For the first time, we have measured anti-Stokes spectral shifts which turn out to appreciably exceed the Rayleigh line widths in those liquids. It is shown that the amplification effect is provided predominantly by thermally induced coherent polarisation oscillations, while the dynamic interference temperature grating causes the formation of a self-induced optical cavity inside the interaction region.

Reflection from a free carrier front via an intraband indirect photonic transition

The reflection of light from moving boundaries is of interest both fundamentally and for applications in frequency conversion, but typically requires high pump power. By using a dispersion-engineered silicon photonic crystal waveguide, we are able to achieve a propagating free carrier front with only a moderate on-chip peak power of 6 W in a 6 ps-long pump pulse. We employ an intraband indirect photonic transition of a co-propagating probe, whereby the probe practically escapes from the front in the forward direction. This forward reflection has up to 35% efficiency and it is accompanied by a strong frequency upshift, which significantly exceeds that expected from the refractive index change and which is a function of group velocity, waveguide dispersion and pump power. Pump, probe and shifted probe all are around 1.5 µm wavelength which opens new possibilities for “on-chip” frequency manipulation and all-optical switching in optical telecommunications.

Excitation of half-integer up-shifted decay channel and quasi-mode in plasma edge for high power electron Bernstein wave heating scenario

Electron Bernstein waves (EBW) consist of promising tools in driving localized off-axis current needed for sustained operation as well as effective selective heating scenarios in advanced over dense fusion plasmas like spherical tori and stellarators by applying high power radio frequency waves within the range of Megawatts. Here some serious non-linear effects like parametric decay modes are highly expect-able which have been extensively studied theoretically and experimentally. In general, the decay of an EBW depends on the ratio of the incident frequency and electron cyclotron frequency. At ratios less than two, parametric decay leads to a lower hybrid wave (or an ion Bernstein wave) and EBWs at a lower frequency. For ratios more than two, the daughter waves constitute either an electron cyclotron quasi-mode and another EBW or an ion wave and EBW. However, in contrast with these decay patterns, the excitation of an unusual up-shifted frequency decay channel for the ratio less than two is demonstrated in this study which is totally different as to its generation and persistence. It is shown that this mode varies from the conventional parametric decay channels which necessarily satisfy the matching conditions in frequency and wave-vector. Moreover, the excitation of some less-known local non-propagating quasi-modes (virtual modes) through weak-turbulence theory and their contributions to energy leakage from conversion process leading the reduction in conversion efficiency is assessed.

Contact-based and spheroidal vibrational modes of a hexagonal monolayer of microspheres on a substrate

We analytically study acoustic modes of a close-packed hexagonal lattice of spheres adhered to a substrate, propagating along a high-symmetry direction. The model, accounting for both normal and shear coupling between the spheres and between the spheres and the substrate, yields three contact-based vibrational modes involving both translational and rotational motion of the spheres. In addition to contact-based modes, we also study the effect of sphere–substrate and sphere–sphere contacts on spheroidal vibrational modes of the spheres using a perturbative approach. The sphere–substrate interaction results in a frequency upshift for the modes having a non-zero displacement at the contact point with the substrate as well as mode-splitting for some of the degenerate modes of the free sphere. Sphere–sphere interactions result in dispersion of spheroidal modes. Analytical dispersion relations for both contact-based and spheroidal modes are presented and compared with results obtained for a square lattice.

X-ray structure, spectral characteristics, thermal and redox behavior of quinoline encapsulated in sulfonatocalix[4]arene

Structure and spectral characteristics of the inclusion complex between quinoline guest and the host para-sulfonatocalix[4]arene (SCX4) have been studied employing single crystal X-ray diffraction, 1H NMR, fluorescence, cyclic voltammetry and TG-DTA experiments. The crystal structure analysis of the inclusion complex Q⊂SCX4 revealed partial encapsulation of one of the quinoline (guest) with its pyridine moiety confined within the SCX4 cavity via CH∙∙∙π and CH∙∙∙O interactions which reflect in the deshielding of guest protons in its 1H NMR spectra. Host-guest binding emerges with signature in frequency up-shift of the characteristic Ar-OH and SO3− stretchings in measured infrared spectra. Inclusion phenomena brings forth remarkable enhancement in fluorescence of quinoline dye. TG-DTA experiments showed that the complex is thermally stable. The cyclic voltammetry experiments suggest the complexation is diffusion controlled. On the theoretical front the ωB97x-D based density functional theory points to the hydrogen bonding cooperativity in the lower and upper rims of the SCX4 and further provides molecular insights for supramolecular binding in the host-guest complex. The inferences on the structure and vibrational spectra drawn from experiments are corroborated by theoretical calculations.