Frequencies Of Longitudinal Modes Research Articles

Phonon frequencies of tetragonally strained PbTiO3 from first principles

First-principles total-energy calculations based on density functional theory within the local-density approximation were employed to investigate transverse and longitudinal optical phonon mode frequencies of ferroelectric PbTiO3 as a function of the aspect ratio of the tetragonal unit cell. Systematic frequency shifts concern practically all polar-mode frequencies. Variation of c/a ratio from 1 to 1.13 is also accompanied by considerable phonon eigenvector changes. Results can be compared with optical spectroscopy investigations of strained PbTiO3 epitaxial thin films.

Les kystes hydatiques thoraciques extrapulmonaires

The infrared reflectivity and transmittance and Raman scattering in Ga3InSe4 layered crystals were investigated in the frequency ranges of 100–400, 400–4000 and 25–500 cm−1. The refractive and absorption indices, the frequencies of transverse and longitudinal optical modes, high- and low-frequency dielectric constants were obtained from the analysis of the IR reflectivity spectra. The bands observed in IR transmittance spectra were interpreted in terms of two-phonon absorption processes.

Infrared and Raman scattering spectra of layered structured Ga3InSe4 crystals

The infrared reflectivity and transmittance and Raman scattering in Ga3InSe4 layered crystals were investigated in the frequency ranges of 100–400, 400–4000 and 25–500cm−1. The refractive and absorption indices, the frequencies of transverse and longitudinal optical modes, high- and low-frequency dielectric constants were obtained from the analysis of the IR reflectivity spectra. The bands observed in IR transmittance spectra were interpreted in terms of two-phonon absorption processes.

Micro-Brillouin spectroscopy mapping of the residual density field induced by Vickers indentation in a soda-lime silicate glass

High-resolution Brillouin scattering is used to achieve 3-dimensional maps of the longitudinal acoustic mode frequency shift in soda-lime silicate glasses subject to Vickers indentations. Assuming that residual stress-induced effects are simply proportional to density changes, residual densification fields are obtained. The density gradient is nearly isotropic, confirming earlier optical observations made on a similar glass. The results show that Brillouin micro-spectroscopy opens the way to a fully quantitative comparison of experimental data with predictions of mechanical models for the identification of a constitutive law.

Rapidly swept continuous-wave cavity-ringdown spectroscopy

Continuous-wave (cw) cavity-ringdown (CRD) spectroscopy provides a highly sensitive way to measure optical absorption by observing the decay rate of light from a high-finesse optical cavity containing the sample of interest (usually gas-phase molecules). In rapidly swept cw-CRD spectroscopy, optical build-up and subsequent ringdown decay are initiated by rapidly sweeping the cavity length or the wavelength of the monochromatic tunable cw laser radiation, thereby establishing and interrupting optical resonance between the laser light and the longitudinal-mode frequencies of the cavity. We review the experimental methodology and applications of this technique, indicating its advantages and prospects for spectroscopic sensing.

Effects of dimensional parameters and various boundary conditions on axisymmetric vibrations of multi-walled carbon nanotubes using a continuum model

Axisymmetric vibrations of multi-walled carbon nanotubes (MWCNTs) with finite length are investigated in this paper. A multi-walled carbon nanotube is modeled with multiple elastic isotropic shells. Based on a continuum model and considering van der Waals forces between tubes, a two-dimensional finite element model is developed to obtain axisymmetric natural frequencies and mode shapes of MWCNTs. First, the axisymmetric vibrational characteristics of single-walled carbon nanotubes are investigated, and then, they are compared with those of MWCNTs. The effects of van der Waals forces on radial vibration of MWCNTs are also explained. Moreover, influences of end conditions on radial and axial natural frequencies of carbon nanotubes (CNTs) with wide range of length-to-thickness ratio are studied by considering the free-free (F-F) and simply supported (S-S) end conditions. Besides, it is focused on dependence of axisymmetric mode frequencies on dimensional parameters such as length, diameter, as well as number of layers of MWCNTs. Through this, explicit expressions are found for calculating the radial breathing mode and longitudinal mode frequencies of MWCNTs.

Multistable monochromatic laser solitons

We study the spectral properties of stationary laser solitons (LSs) generated in two broad-area vertical cavity surface emitting lasers coupled to each other in face-to-face configuration [P. Genevet et al., Phys. Rev. Lett. 101, 123905 (2008)]. We demonstrate experimentally that LS emission occurs on a single longitudinal mode frequency of the compound cavity. Multistability is reported among differently ``colored'' LSs. We also develop a theoretical model beyond the single longitudinal mode approximation whose numerical simulation results are in good agreement with the experimental observations.

Effect of Cross-Sectional Area Discontinuities in Closed Hard-Walled Ducts on Frequency of Longitudinal Modes

A simple analytical method is developed to estimate frequencies of longitudinal modes in closed hard-walled ducts with discontinuities in a cross-sectional area. The approach adopted is based on a general expression for the acoustic impedance for a plane wave motion in a duct and conditions of impedance continuity at duct discontinuities. Formulae for mode frequencies in a form of transcendental equations were found for one, two and three discontinuities in a duct cross-section. An accuracy of the method was checked by a comparison of analytic predictions with calculation data obtained by use of numerical implementation based on the forced oscillator method with a finite difference algorithm.

Analysis of transient fluid slosh in partly-filled tanks with and without baffles: Part 2 – role of baffles

Baffles tend to suppress the forces and moments caused by fluid slosh in partly filled tank trucks, thus increasing their directional stability limits. The anti-slosh properties of different baffles designs are investigated through transient slosh analysis of a partly-filled 'Reuleaux triangle' cross-section tank. The effectiveness of baffles is evaluated in terms of fundamental slosh frequency, and forces and moments. The results show that the slosh natural frequencies and magnitudes of slosh forces and moments strongly depend upon the baffle design, fill volume and excitation. The longitudinal mode frequency of the baffled tank can be three times that of the unbaffled tank, while baffles could reduce peak longitudinal force by 39%. The partial baffles could be more effective under higher fill levels. Variations in baffle porosity resulted in only minor changes in peak longitudinal slosh force, but significant effect on steady-state pitch moment.

Vibrational dynamics of Zr-based bulk metallic glasses

The vibrational dynamics of some Zr-based bulkmetallic glasses were studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). The well recognized model potential is employed successfully to explain electron-ion interaction in the metallic glass. The present findings of phonon dispersion curve are found to be in fair agreement with available theoretical as well as experimental data. The thermodynamic properties obtained by the HB and TG approaches are found to be much lower than those obtained by the BS approach.

Radial compression of a non-neutral plasma in a cusp trap for antihydrogen synthesis

We present the radial compression of an electron plasma by using a rotating wall in a spindle cusp region of an axisymmetric magnetic quadrupole. The compression rate depended on the rotating frequencies and had a broad peak extending on both sides of a longitudinal (1,0) mode frequency, which was the only observed characteristic frequency. The formation of the high-density plasma is one of the important milestones for the antihydrogen formation and extraction of ultraslow spin-polarized antihydrogen beams in the spindle cusp.

Vibrational dynamics of non-crystalline glassy alloys

The vibrational dynamics of three Ca-based non-crystalline alloys viz. Ca70Mg30, Ca70Zn30 and Ca60Al40 have been studied at room temperature in terms of the phonon eigen frequencies of longitudinal and transverse modes, employing three theoretical formulations given by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). Five local field correction functions viz. Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used for the first time in the present investigation to study the screening influence on the aforesaid properties. The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard’s Law. Long wavelength limits of the phonon modes are used to investigate the elastic and thermal properties of the system. The low temperature specific heat is also calculated from the elastic limit of the phonon dispersion curves (PDCs). The present findings of the PDCs of Ca70Mg30 glass are found in fair agreement with available theoretical and experimental data.

Investigation of the peculiarities in the polarized reflectance spectra of some Tutton salt monoclinic single crystals using dispersion analysis

Dispersion analysis in the ν 3(SO 4 2−) frequency region of two Tutton salt monoclinic single crystals, K 2Ni(SO 4) 2·6H 2O and (NH 4) 2Ni(SO 4) 2·6H 2O, was performed. Employing analytical expressions for the dielectric tensor and the reflectance function valid for monoclinic crystals, oscillator parameters like, transversal mode frequencies and the corresponding attenuation constants, transition moments orientation and oscillator strengths as well as longitudinal mode frequencies and the corresponding transition moment orientations were obtained. These oscillator parameters were used in simulations in order to explain certain peculiarities in the reflectance spectra occurring with directional changes of the polarization vector. From the simulations it follows that the appearance of spectra with two totally overlapped bands (having quite different oscillator strengths) depends particularly on the orientation of the longitudinal transition moment of the mode with the smaller LO–TO splitting.

The study on diode-pumped two-frequency solid-state laser with tunable frequency difference

The laser diode pumped two-frequency solid-state laser with tunable frequencydifference is investigated, the medium is a 1at% doped 2-mm thick Nd:YAG chip. The condition of stable two-frequency oscillation operation is analyzed, the polarization is calculated by Jones matrix in different locations at the resonator. It is proved that the two-frequency electric field vectors are orthogonally polarized everywhere, the frequency difference tuning can be realized by changing the angle between the fast axes of two quarter-wave plates. In the experiment, single-frequency oscillation was obtained with the help of an etalon, then longitudinal mode frequency splitting resulted in the two-frequency oscillating operation by inserting two quarter-wave plates. The obtained maximum frequency difference was 1.3GHz, the minimal was 50MHz because of the strong mode competition. Due to the loss anisotropy of the etalon, the output power is not very stable when tuning the frequency difference, 85mW two-frequency output power was obtained with 100MHz beat note.

Mathematical modeling of tunable TEA CO 2 lasers

A mathematical model, based on the Landau–Teller equations of six-temperature model for the CO 2–N 2–He–CO system, to describe the process of dynamic emission in tunable TEA CO 2 lasers is introduced. In this model, the Landau–Teller equations are rewritten with regard to fine longitudinal mode frequencies in the laser resonator. These revised equations can be utilized to estimate the laser output spectra as well as other laser output pulse parameters. Examples are given to show the modeling results of non-tunable, grating tuned or injection-locking TEA CO 2 lasers.

Seed injection and frequency-locked Nd:YAG laser for direct detection wind lidar

The single longitudinal mode operation and frequency stability are essential for the laser transmitter used in the Doppler lidar. We devise a seed injection, frequency tunable and locked Q-switched Nd:YAG laser for the direct detection Doppler lidar. By implementation of the dual-wavelength seed laser and iodine-based PID frequency-locking technique, the frequency-stabilized seed laser is robust to interference and can be locked within 200 kHz for 3 h. The stable output of single longitudinal mode of the frequency-doubled pulsed laser makes it possible to achieve operational wind measurement.

Oxygen behavior in aluminum nitride

The infrared lattice-vibration spectra of three polycrystalline samples of wurtzite AlN differing in their oxygen contamination have been studied by measuring the room-temperature reflectivity at near-normal incidence in the 400-3000cm−1 frequency range using unpolarized light. A type of highly-contaminated-material reflectivity spectrum has been observed. Two-mode behavior has been observed at low oxygen concentration, one-mode behavior tends to be dominant when the oxygen concentration increases and only one-mode behavior has been observed at high oxygen concentration. Otherwise, a careful analysis of the data using the Kramers-Kronig technique and classical dispersion theory gives, in addition to the transverse and longitudinal mode frequencies, two in-band resonance modes attributed to oxygen point defects in AlN. Changes in the frequencies of these modes with oxygen concentration are interpreted as a transition in the oxygen accommodation defect as the concentration of oxygen increases. A model for the behavior of oxygen in AlN is proposed.

Single-particle and collective excitations in a charged Bose gas at finite temperature

The main focus of this work is on the predictions made by the dielectric formalism in regard to the relationship between single-particle and collective excitation spectra in a gas of pointlike charged bosons at finite temperature $T$ below the critical region of Bose-Einstein condensation. Illustrative numerical results at weak coupling $({r}_{s}=1)$ are presented within the random phase approximation. We show that within this approach the single-particle spectrum forms a continuum extending from the transverse to the longitudinal plasma mode frequency and leading to a double-peak structure as $T$ increases, whereas the density fluctuation spectrum consists of a single broad peak. We also discuss the momentum distribution and the superfluidity of the gas.

Terahertz time domain magneto-optical ellipsometry in reflection geometry

We propose and examine a method to reveal the diagonal and off-diagonal components of a dielectric tensor from THz magneto-optical Kerr effect (MOKE) measurements. The proposed method, which is based on time-domain THz measurement, does not involve any assumption on the magnitude of the magneto-optical constant. We apply this method to determine the dielectric tensor of $n$-type InAs in the spectral range from 0.5 to 2.5 THz and compare the results with those obtained in the framework of the conventional small magneto-optical response approximation. (SMRA). It is shown that when the probe frequency is lower than the frequency of longitudinal electromagnetic modes in the medium (e.g., below magnetoplasma or longitudinal phonon resonance) the SMRA-based analysis should be replaced with the method we developed even for small magneto-optical signals.

Optical-Pulse-Injection-Induced 40 GHz Photonic Frequency Multiplication in Erbium-Doped Fiber Laser

The generation of a 40 GHz regeneratively amplified and frequency-multiplied optical pulse train from an erbium-doped fiber ring laser is demonstrated. This is achieved by seeding a 1 GHz gain-switched Fabry–Perot laser diode and detuning its repetition frequency to coincide with the harmonic resonant cavity mode. The peak power of frequency-multiplied erbium-doped fiber lasers (EDFL) pulses increases from 80 mW to 230 mW as the modulation level of the Fabry–Perot laser diode (FPLD) increases from 18 dBm to 30 dBm. The pulsewidth and peak power are 10 ps and 5 mW at a repetition rate of 40 GHz. The EDFL longitudinal mode frequency fluctuation is within ±2.5 kHz during 2 h. The frequency-multiplied EDFL pulses exhibit relatively low phase noises of -95 dBc/Hz and -120 dBc/Hz at offset frequencies of 10 kHz and 1 MHz, respectively. The associated timing jitter of the EDFL pulses exponentially increases from 0.6 ps to beyond 5.8 ps as the frequency multiplication order increases from 1 to 40.