Frequency Shifts Of Modes Research Articles

Do Material Discontinuities in Silica Affect Vibration Modes?

Structural properties of bioinorganic composites are of current interest in the areas of drug delivery, bone repair, and biomimetics. In such composite systems, structural analysis is enhanced when we combine methods of spectroscopy and simulation. Depending on size and shape, structural discontinuities of inorganic matter may modulate the optical response of a bound molecule. Using density functional theory, we explore the effects of a local field next to the surface of a silica cluster on frequencies of methyl stretching modes of associated methanols. Computation results predict that the electrostatic potential modulated by structural discontinuities of silica should not contribute to any systematic frequency shifts for normal modes of a guest molecule. Regardless of position, the methyl stretching modes of methanol demonstrate sensitivity only to the local chemistry of bonding with silanols, which may lead either to a low or high frequency shift for vibrations. In support, experimental studies of deuterated methanol at impurity levels in water show uniform broadening of resonances of carbon-deuterium stretching modes in the presence of both crystalline and amorphous silica nanoparticles. The significance of these findings is that the spectral responses of guest molecules on such surfaces should not be subject to bias introduced by edge effects.

Controlled hole burning for a cavity field with a single atom

We present a simple method of realizing controlled hole burning for a cavity mode in Fock space by using a single two-level atom. In the scheme, the atom is driven by a classical field and dispersively interacts with the cavity mode. Due to the photon number-dependent atomic transition frequency shift, the atom is excited only for a specific Fock state. As a result, the detection of the atom remaining in the ground state projects the cavity to the state with a desired hole in Fock space. An important feature of the scheme is that multiple holes can be burnt at the same time with a single atom driven by a pulse composed of multiple frequency components.

Suppression of thermal transients in advanced LIGO interferometers using CO2 laser preheating

In high optical power interferometric gravitational wave detectors, such as Advanced LIGO, the thermal effects due to optical absorption in the mirror coatings and the slow thermal response of fused silica substrate cause time dependent changes in the mirror profile. After locking, high optical power builds up in the arm cavities. Absorption induced heating causes optical cavity transverse mode frequencies to drift over a period of hours, relative to the fundamental mode. At high optical power this can cause time dependent transient parametric instability, which can lead to interferometer disfunction. In this paper, we model the use of CO2 laser heating designed to enable the interferometer to be maintained in a thermal condition such that transient changes in the mirrors are greatly reduced. This can minimize transient parametric instability and compensate dark port power fluctuations. Modeling results are presented for both single compensation where a CO2 laser acting on one test mass per cavity, and double compensation using one CO2 laser for each test mass. Using parameters of the LIGO Hanford Observatory X-arm as an example, single compensation allows the maximum mode frequency shift to be limited to 6% of its uncompensated value. However, single compensation causes transient degradation of the contrast defect. Double compensation minimise contrast defect degradation and reduces transients to less than 1% if the CO2 laser spot is positioned within 2 mm of the cavity beam position.

Intermodal Coupling as a Probe for Detecting Nanomechanical Modes

Nanoelectromechanical systems provide ultrahigh performance in sensing applications. The sensing performance and functionality can be enhanced by utilizing more than one resonance mode of a nanoelectromechanical-systems device. However, it is often challenging to measure mechanical modes at high frequencies or modes that couple weakly to output transducers. In this paper, we propose the use of intermodal coupling as a mechanism to enable the detection of such modes. To implement this method, a probe mode is continuously driven and monitored using a phase-locked loop, while an auxiliary drive signal scans for other modes. Each time the auxiliary drive signal excites the corresponding mode by matching the mechanical frequency, the effective tension within the structure increases, which in turn causes a frequency shift in the probe mode. The location and width of these frequency shifts can be used to determine the frequency and quality factor of mechanical modes indirectly. Intermodal coupling can be used as a tool to obtain the spectrum of a mechanical structure even if some of these modes cannot be detected conventionally.

Flying particle microlaser and temperature sensor in hollow-core photonic crystal fiber.

Whispering-gallery mode (WGM) resonators combine small optical mode volumes with narrow resonance linewidths, making them exciting platforms for a variety of applications. Here we report a flying WGM microlaser, realized by optically trapping a dye-doped microparticle within a liquid-filled hollow-core photonic crystal fiber (HC-PCF) using a CW laser and then pumping it with a pulsed excitation laser whose wavelength matches the absorption band of the dye. The laser emits into core-guided modes that can be detected at the endfaces of the HC-PCF. Using radiation forces, the microlaser can be freely propelled along the HC-PCF over multi-centimeter distances-orders of magnitude farther than in previous experiments where tweezers and fiber traps were used. The system can be used to measure temperature with high spatial resolution, by exploiting the temperature-dependent frequency shift of the lasing modes, and may also permit precise delivery of light to remote locations.

Current tunable barium hexaferrite millimeter wave resonator

AbstractThis report is on non‐linear magneto‐electric (ME) interactions due to an electric current in single crystal M‐type barium hexaferrite (BaM). The interaction results in variations in the magnetic order parameters and manifests as tuning of magnetic modes in a BaM resonator in the U‐band. A DC current along the c‐axis of the ferrite is found to tune the frequency of the magnetic mode by 400 MHz when the sample is in the single‐domain state and by 70 MHz in the multi‐domain state for currents up to 20 mA and applied voltages up to 75 V. The current tuning of the frequency is found to be linear with electric power for both single‐domain and multi‐domain resonances. The shift in mode frequency due to current is found to be an order of magnitude higher than shift that could be attributed to Joule heating. The current tuning of the resonator demonstrated here is of interest for miniature, self‐biased millimeter wave ferrite devices.

Measurement of molecular absorption spectrum with a laser locked on a high-finesse cavity

High-resolution and high-sensitivity molecular spectroscopy is widely used in fundamental molecular physics, atmospheric studies, remote sensing, industrial process monitoring, and medical diagnostics. Accurate determination of the parameters of molecule absorption lines, such as line positions, line strengths, line widths and profiles, is essential to support these studies and applications. For example, in order to retrieve the column density of carbon dioxide with a precision of one part per million (ppm), we need laboratory data of line positions with a uncertainty lower than 0.3 MHz and line intensities with a relative accuracy better than 0.5%. Here we present precision spectroscopy of molecules using a laser locked with a high-finesse cavity. The cavity made of invar is thermo-stabilized to reduce the drifts of its length and the cavity mode frequencies. The frequency of the probe laser is locked on a longitudinal mode of the cavity by using the Pound-Drever-Hall method. Another beam from the probe laser, which is frequency shifted and on resonance with a nearby longitudinal mode of the cavity, is used for cavity ring-down spectrum (CRDS) measurement. The CRDS absorption spectrum is recorded by stepping the modulation frequency of a fiber electro-optic modulator in increment of the mode spacing of the cavity. Note that the cavity mode frequencies are shifted due to the dispersion introduced by the absorption lines. Prior to the CRDS measurements, the transmittance spectra of the cavity modes are recorded by scanning the probe laser frequencies over the resonance, which allows the determination of the cavity mode frequencies with an accuracy at a Hz level. Therefore, a dispersion spectrum is also obtained using the same setup by measuring the frequency shifts of cavity modes of the samples with and without absorption. The absolute frequency of the probe laser is determined by an optical frequency comb referring to a GPS-disciplined rubidium clock. The long term drift of beat frequency between the optical frequency comb and the probe laser is measured to be about 1.8 MHz per hour, which is consistent with the thermal expansion of the cavity under a temperature drift of 50 mK. The performance of the spectrometer is demonstrated by measuring the Doppler-broadened spectra of CO2 around 6470.42 cm-1. Precise spectroscopic parameters are derived from both the absorption and dispersion spectra recorded by the same spectrometer. The line position is determined with an accuracy of 0.18 MHz, which is over one order of magnitude better than those given in previous studies and spectral databases.

Raman modes of carbonate minerals as pressure and temperature gauges up to 6 GPa and 500°C

Diamond anvil cell (DAC) experiments focusing on the solubility of carbonates and aqueous carbon speciation at subduction zones require pressure monitoring with sensitive, chemically inert sensors. Commonly used pressure indicators are either too insensitive or prone to contaminate pressure-transmitting media due to their increased solubility at high pressure and/or temperature (P/T). Here, the P- and T-induced frequency shifts of the Raman vibrational modes of natural crystalline carbonate minerals aragonite, calcite, dolomite, magnesite, rhodochrosite, and siderite have been calibrated for application as Raman spectroscopic P and T sensors in DACs up to 500°C and 6 GPa. The shifts of all modes are quasi-constant over the observed P and T ranges and are generally less prominent for internal modes than for external modes. Our method provides a sensitive and robust alternative to traditional pressure calibrants, and has three principal advantages: (1) higher sensitivity (for particular Raman vibrational modes), (2) monitoring P/T -induced shifts of several modes allows even more accurate P/T determination, and (3) no contamination of pressure-transmitting media by foreign materials can occur. Additionally, the isobaric and isothermal equivalent of the Gruneisen parameter and the anharmonic parameter for each of the traced modes have been determined.

Effect of Zeeman Depopulation Pumping on Cycling Atomic Transitions

The results of an investigation of fluorescence signal at 6S1/2 (Fg = 4) → 6P3/2 (Fe = 5) transition of D2 line of atomic Cs vapor versus the magnetic field (up to B = 90 G), directed along the linear polarization of exciting light are presented. The recorded reduction of fluorescence in the magnetic field, which is especially strong at high intensity of laser radiation, is explained by conversion of the Zeeman optical pumping (the alignment) into the depopulation pumping under conditions, when the Zeeman frequency shift of individual transitions between magnetic sublevels exceeds the homogeneous width of transition. In consequence, the cycling hyperfine transition Fg = 4 → Fe = 5 is transformed into an open one.

Generation of coherent magnons in NiO stimulated by EUV pulses from a seeded free-electron laser

The recent development of seeded free-electron lasers made possible the implementation of a new class of time-resolved experiments, strictly requiring pulses characterized by quasi full coherence. Here, circularly polarized EUV pulses have been used to launch magnetic excitations (magnons) in a thin film of nickel oxide (NiO), subsequently revealed via optical techniques. The main novelty of this work is that these collective modes have been excited using EUV pulses resonant at core electrons energies. Switching the EUV polarization, a flip equal to Pi in the mode polarity has been observed, which can be ascribed to an optomagnetic effect, as well as a mode frequency shift, scaling as a function of the absorption cross section between core electrons and circularly polarized photons. A phenomenological model supports these findings, too.

Numerical analysis for attenuation effects of perforated plates on thermoacoustic instability in the multiple flame combustor

In the present study, the FDF-based approach together with the Helmholtz solver has been applied to precisely analyze the attenuation effects of the perforated plates on thermoacoustic instability in the lab-scale multiple flame combustor. In order to effectively suppress the combustion instability, we derive the optimal damping conditions for perforated plates in terms of the porosity and cavity length. To overcome the weaknesses of the Howe model, the Luong model is utilized for an impedance boundary condition of perforated plates. After then, we validated our methodology to the impedance tube, which shows the predicted results are well agreed with the experimental data for all validation cases Another new approach for the dual perforated plates has been proposed to enlarge the absorption bandwidth in a wider frequency regime. Numerical results clearly indicate that since the dual plates are tuned at two different target frequencies, the system can have two maximum absorption points and their combined effects in a frequency range. This makes the dual-plate method capable of stabilizing the combustion instability in the much wider frequency range than does the single-plate scheme. Therefore, it is expected that the dual-plate methodology would be more effective to suppress the unexpected nonlinear behavior such as the mode change, frequency shift, and hysteresis thanks to the wide attenuation coverage.

Determination of stress components in 4H-SiC power devices via Raman spectroscopy

The stress dependencies of the phonon modes in a 4H silicon carbide (SiC) crystal were investigated. The deformation potentials of the A1(TO), E2, and E1(TO) modes were determined on the basis of uniaxial stress tests. The A1(TO) mode was sensitive to stress along the c axis, whereas the E1(TO) and E2 modes exhibited larger dependencies on the stress perpendicular to the c axis than the A1(TO) mode as expected from their atomic displacements. The coefficient of the frequency shift in the E2 mode for an isotropic biaxial stress in the c plane was determined to be −323 MPa/cm−1. We applied cross-sectional Raman measurements to SiC metal-oxide-semiconductor field-effect transistors. The horizontal and vertical stress components, σ11 and σ33, were derived from the frequency shifts of the E2 and A1(TO) modes using the deformation-potential constants. A compressive horizontal stress was observed near the interface between the SiC chip and the metals. The observed compressive stress increased as the temperature decreased. The main cause for the compressive horizontal stress at low temperature is considered to be the difference in the coefficients of thermal expansion of the SiC chip and the metals. The results suggest that the temperature of the fabrication process is one of the key factors for achieving a reduction in the thermal stress in the SiC power devices.

Pressure‐dependent Raman modes near the cubic‐tetragonal transition in strontium titanate

AbstractThe pressure dependence of the Raman frequency shifts of various Raman modes is calculated at room temperature using the volume data from the literature for the cubic‐tetragonal transition in SrTiO3. The isothermal mode Grüneisen parameters of those Raman modes are obtained, which decrease with increasing pressure for this molecular crystal. Calculated Raman frequencies are then used to predict the damping constant and the inverse relaxation time of those Raman modes as a function of pressure by means of the pseudospin‐phonon (PS) coupled model and the energy fluctuation (EF) model to describe the cubic‐tetragonal transition in SrTiO3. Also, the values of the activation energy are extracted for the Raman modes studied using both models (PS and EF). Our predicted damping constant and the inverse relaxation time for the Raman modes, can be compared with the experimental measurements close to the cubic‐tetragonal transition in SrTiO3.

Characterizing Chemical Similarity with Vibrational Spectroscopy: New Insights into the Substituent Effects in Monosubstituted Benzenes.

A novel approach is presented to assess chemical similarity based the local vibrational mode analysis developed by Konkoli and Cremer. The local mode frequency shifts are introduced as similarity descriptors that are sensitive to any electronic structure change. In this work, 59 different monosubstituted benzenes are compared. For a subset of 43 compounds, for which experimental data was available, the ortho-/para- and meta-directing effect in electrophilic aromatic substitution reactions could be correctly reproduced, proving the robustness of the new similarity index. For the remaining 16 compounds, the directing effect was predicted. The new approach is broadly applicable to all compounds for which either experimental or calculated vibrational frequency information is available.

Highly Luminous and Thermally Stable Mg-Substituted Ca2-xMgxSiO4:Ce (0 ≤ x ≤ 1) Phosphor for NUV-LEDs.

Blue-emitting Ca2-xMgxSiO4:Ce (0.0 ≤ x ≤ 1.0) phosphors were successfully synthesized and characterized. Rietveld refinement revealed that four main phases exist within the solid-solution range of CaO-MgO-SiO2, namely, β-Ca2SiO4 (Mg (x) = 0.0), Ca14Mg2(SiO4)8 (Mg (x) = 0.25), Ca3Mg(SiO4)2 (Mg (x) = 0.5), and CaMgSiO4 (Mg (x) = 1.0). The variation of the IR modes was more prominent with increasing Mg2+ content in the Ca2-xMgxSiO4 materials. The sharing of O atoms of the SiO4-tetrahedra by the MgO6-octahedra induced weakening of the Si-O bonds, which resulted in the red shift of the [SiO4] internal modes and appearance of a Mg-O stretching vibration at ∼418 cm-1. Raman measurement revealed that the change of the Ca-O bond lengths because of the Mg2+-substitution directly reflected the frequency shift of the Si-O stretching-Raman modes. Notably, the thermal stability of Ca2-xMgxSiO4:Ce (Mg (x) > 0.0) phosphors was superior to that of β-Ca2SiO4:Ce (Mg (x) = 0.0) as confirmed by temperature-dependent photoluminescence (PL) measurements. This indicated that Mg2+ ions play an important role in enhancement of the thermal stability. In combination with the results from PL and electroluminescence (EL), it was elucidated that the luminous efficiency of Ca2-xMgxSiO4:Ce (Mg (x) = 0.1) was approximately twice as much as β-Ca2SiO4:Ce (Mg (x) = 0.00), directly indicating a "Mg2+-substitution effect". The large enhancements of PL, EL, and thermal stability because of Mg2+-substitution may provide a platform in the discovery of more efficient phosphors for NUV-LEDs.

Feasibility of an optical fiber clock

We explore the feasibility of a compact high-precision Hg atomic clock based on a hollow core optical fiber. We evaluate the sensitivity of the $^1S_0$-$^3P_0$ clock transition in Hg and other divalent atoms to the fiber inner core surface at non-zero temperatures. The Casimir-Polder interaction induced $^1S_0$-$^3P_0$ transition frequency shift is calculated for the atom inside the hollow capillary as a function of atomic position, capillary material, and geometric parameters. For $^{199}\mathrm{Hg}$ atoms on the axis of a silica capillary with inner radius $\geq 15 \,\mu \mathrm{m}$ and optimally chosen thickness $d\sim 1 \,\mu \mathrm{m}$, the atom-surface interaction induced $^1S_0$-$^3P_0$ clock transition frequency shift can be kept on the level $\delta\nu/\nu_{\mathrm{Hg}} \sim10^{-19}$. We also estimate the atom loss and heating due to the collisions with the buffer gas, lattice intensity noise induced heating, spontaneous photon scattering, and residual birefringence induced frequency shifts.

Resonant Raman scattering study of BexZn1−xO thin films grown on sapphire by molecular beam epitaxy

Resonance Raman spectra of Be[Formula: see text]Zn[Formula: see text]O alloy materials were studied using 325 nm Laser. The research showed that the Raman spectra of Be[Formula: see text]Zn[Formula: see text]O alloys presents a dual-mode vibration. Compare Be[Formula: see text]Zn[Formula: see text]O alloy with ZnO single crystal, the A1 (LO) phonon vibration mode of Be[Formula: see text]Zn[Formula: see text]O alloy moved to the larger wave number direction. The position of A1 (LO) phonon vibration modes of Be[Formula: see text]Zn[Formula: see text]O and Be[Formula: see text]Zn[Formula: see text]O was 580 cm[Formula: see text] and 582 cm[Formula: see text], respectively. In addition, the temperature-dependent Raman spectroscopy was employed for Be[Formula: see text]Zn[Formula: see text]O, and the phonon mode frequency shift with temperature was studied in detail. Finally, the stability of the polar and nonpolar Be[Formula: see text]Zn[Formula: see text]O alloy materials was studied using resonance Raman spectroscopy. The results showed that the A1 (LO) phonon mode frequency of polar Be[Formula: see text]Zn[Formula: see text]O alloy remained in the same position, while the nonpolar Be[Formula: see text]Zn[Formula: see text]O alloys moved nearly 3.5 cm[Formula: see text] to larger direction after being placed in the air for two years. The reason may be that the stability of the nonpolar Be[Formula: see text]Zn[Formula: see text]O alloy is relatively poor upon interaction with molecule such as H2O, O2 in the air.

Constraining new physics models with isotope shift spectroscopy

Isotope shifts of transition frequencies in atoms constrain generic long- and intermediate-range interactions. We focus on new physics scenarios that can be most strongly constrained by King Linearity Violation such as models with B-L vector bosons, Higgs portal and chameleon. With the anticipated precision, King Linearity Violation has the potential to set the strongest laboratory bounds on these models in some regions of parameter space. Furthermore, we show that this method can probe the couplings relevant for the protophobic interpretation of the recently reported Be anomaly. We extend the formalism to include an arbitrary number of transitions and isotope pairs and fit the new physics coupling to the currently available isotope shift measurements.

Inelastic light scattering of ferroelectric Sr2(Nb1-xTax)2O7 crystals at high temperatures

ABSTRACTThe lattice instability and elastic anomaly of a ferroelectric and incommensurate (IC) phase transitions of Sr2(Nb1-xTax)2O7 single crystals with x = 0.20 and 0.40 were studied by Raman and Brillouin scattering over the broad temperature range from room temperature to 1400°C. For a ferroelectric phase transition, Brillouin scattering of the x = 0.20 and 0.40 crystals show the discontinuous change in Brillouin frequency shift of a LA mode related to elastic constant c22 in the vicinity of TC = 1160°C and 910°C, respectively. The Raman scattering of the x = 0.20 and 0.40 crystals shows the remarkable softening of the lowest frequency A1(z) mode at about 50 cm−1 towards TC similar to the Sr2Nb2O7 (x = 0.00) crystal reported previously. It indicates that the displacive nature of a soft optic mode still remains for the composition up to x = 0.40. For the normal to incommensurate (IC) phase transitions, Brillouin frequency shifts of LA modes show the noticeable changes at TIC = 220°C and 265°C, respectively.

An Experimental and Numerical Investigation of the Vibrational Response of a Flanged Cylinder Structure

The paper presents a combined experimental and numerical investigation of the vibrational response of a flanged cylinder structure due to a time-harmonic point excitation. The principle focus of this study was to (1) determine the relative sensitivity of the vibrational response of the cylinder due to variations in the experimental configuration (such as using different vibrational sources, excitation points or complicating structural configurations), and (2) ascertain the level of detail required in the numerical models to accurately replicate the experimental results. Overall, good agreement was achieved between the measured and modelled mode shapes/frequencies up to approximately 1500 Hz, while the experimental results were shown to be largely insensitive to the excitation point or type of mechanical shaker employed. Comparative identification of the measured and modelled cylinder mode shapes allowed for other measured frequency response peaks which did not exhibit discernible modal patterns to be identified from the FEM analysis as either bending modes or internal plate modes for the structure. Finally, it was observed that the contact condition used to model the bolted plates in the structure had a significant effect on the predicted plate modal frequencies, while small amounts of mass loading in the experimental configuration were predicted to cause significant frequency shifts for certain modes.