Noise-induced linewidth in frequency combs

Frequency combs generated by trains of pulses emitted from mode-locked lasers are analyzed when the center time and phase of the pulses undergo noise-induced random walk, which broadens the comb lines. Asymptotic analysis and computation reveal that, when the standard deviation of the center-time jitter of the nth pulse scales as n(p/2) where p is a jitter exponent, the linewidth of the kth comb line scales as k(2/p). The linear-dispersionless (p=1) and pure-soliton (p=3) dynamics in lasers are derived as special cases of this time-frequency duality relation. In addition, the linewidth induced by phase jitter decreases with power P(out), as (P(out))(-1/p).     

The frequency and width of a surface plasmon in a small cluster

The dependence of the frequency and width of a surface plasmon ω_s on the cluster size is analyzed. In the process of the investigation, a large numerical parameter appears that determines the shape of the potential of the electromagnetic field inside the cluster and leads to a wide plateau on the dependence of ω_s on the cluster radius.     

Oscillatory behavior and enhancement of the surface plasmon linewidth in embedded noble metal nanoparticles

We study the Landau damping of the surface plasmon resonance of metallic nanoparticles embedded in different environments of experimental relevance. Important oscillations of the plasmon linewidth as a function of the radius of the nanoparticles are obtained from numerical calculations based on the time dependent local density approximation. These size-oscillations are understood, within a semiclassical approximation, as a consequence of correlations in the spectral density of the nanoparticles. We treat inert matrices, as well as the case with an unoccupied conduction band. In the latter case, the plasmon lifetime is greatly reduced with respect to the inert case, but the non-monotonous size-dependence persists.     

The frequency noise and spectral linewidth in semiconductor ring lasers

Numerical analyses for power spectral density of frequency noise (FN) and spectral linewidth in monolithic semiconductor ring laser (SRL) operating in the bistable unidirectional regime are performed in this paper. The Langevin noise sources for electric field and carrier density fluctuations are also taken into account in the frequency-domain theoretical model. The influences of several important physical parameters on the FN properties and laser linewidth are clearly demonstrated, including the injection current, linewidth enhancement factor and the particular backscattering coefficient. Due to the particular backscattering in SRLs, the calculated linewidths are relatively higher than that from the conventional Henry formula. The laser linewidth shows an exponential relationship with the backscattering strength.     

Cyclotron resonance in a two-dimensional semimetal

Cyclotron resonance in a two-dimensional semimetal has been studied theoretically, keeping in mind recent experiments reported in Z. D. Kvon, S. N. Pamilov, S. D. Ganichev, et al., in Proceedings of the 14th International Conference on Narrow Gap Semiconductors and Systems (Sendai, Japan, 2009). Since the size of the sample is finite, the exciting microwave inhomogeneous and there is a plasma shift of resonance frequency. There are two magnetoplasmon branches in a two-component system, which undergo pseudocrossing under the found criterion. Resonance frequencies and intensities of absorption peaks have been found. The latter are complicated functions of the electron and hole densities.     

Plasma oscillations in a two-dimensional semimetal

Collective oscillations of an electron-hole plasma in a two-dimensional semimetal have been investigated. It has been shown that two undamped branches of plasma oscillations exist under certain conditions on the parameters of the structure. Acoustic plasmons are not damped in a finite wavenumber range. When the Fermi velocities of the electrons and holes are equal to each other, this range expands to the range of the applicability of the theory (the momentum of the plasmon is much lower than the Fermi momenta of the particles).     

Quasiparticle lifetime in a two-dimensional semimetal

The quasiparticle lifetime in a two-dimensional direct band semimetal limited by inelastic Coulomb scattering has been calculated in the case where two types of charge carriers are present. It has been shown that the electron lifetime at low and high concentrations of holes is mainly determined by the electron-hole and electron-electron scattering, respectively.     

Scattering processes in a two-dimensional semimetal

The scattering mechanisms in a two-dimensional semimetal based on a HgTe quantum well, where the electron and hole densities are controlled over a wide range by applying the gate voltage, have been studied. It is shown that impurity scattering prevails in this system at low temperatures. Interparticle scattering (in this case, electrons and holes) has been observed to directly affect the resistance of the metal.     

Explanation of the anomalous behaviour of the k-dependent plasmon linewidth in lithium

The high value and the negative dispersion of the plasmon linewidth in Li at low k, previously believed to be due to grain boundary scattering of very small crystallites, is shown to be caused by interband transitions whose strength depends on the magnitude of the first pseudopotential coefficients.     

Tunability and linewidth sharpening of plasmon resonances on a periodic gold nanowire array coupled to a thin textured silver film

We theoretically study the plasmon mode spectrum of a multilayer structure consisting of a periodic gold nanowire array and a spatially separated thin silver film with periodic slits. Results show that the plasmon mode spectrum of the multilayer structure depends sensitively on the relative lateral displacement of the Au nanowire array with respect to the textured silver film. This is due to the interaction between the localized surface plasmon (LSP) of the nanowire array and the plasmon modes, including the horizontal LSP and the antisymmetric short-range surface plasmon polariton (SPP), of the textured thin silver film. The strong coupling between the LSP and the antisymmetric short-range SPP results in a redshifted plasmon resonance with a significantly narrow linewidth and a large electromagnetic field enhancement. Moreover, the lateral displacement also has a great influence on the spacer layer controlled dipole-surface interaction. Therefore, this relative lateral displacement provides an efficient way to tune the optical properties of the multilayer structure, and this kind of highly tunable nanostructure can be used as a tunable plasmonic filter or a substrate for LSPs sensor.     

Weyl semimetal in a topological insulator multilayer

We propose a simple realization of the three-dimensional (3D) Weyl semimetal phase, utilizing a multilayer structure, composed of identical thin films of a magnetically doped 3D topological insulator, separated by ordinary-insulator spacer layers. We show that the phase diagram of this system contains a Weyl semimetal phase of the simplest possible kind, with only two Dirac nodes of opposite chirality, separated in momentum space, in its band structure. This Weyl semimetal has a finite anomalous Hall conductivity and chiral edge states and occurs as an intermediate phase between an ordinary insulator and a 3D quantum anomalous Hall insulator. We find that the Weyl semimetal has a nonzero dc conductivity at zero temperature, but Drude weight vanishing as T(2), and is thus an unusual metallic phase, characterized by a finite anomalous Hall conductivity and topologically protected edge states.     

Temperature-dependent plasmon excitations in the surface layer of ordered Cu-22.5 at % Mn alloy

Temperature and energy dependences of the characteristic electron energy losses on plasmon excitations are studied in the surface layer of ordered polycrystalline Cu-22.5 at % Mn alloy. Features in the near-surface distribution of Mn are found from an analysis of plasmon excitations and the data of Auger spectroscopy. The observed temperature dependences of the electron energy loss spectra have features in the range of 650–750 K that include the temperature of atomic disordering (T _k = 675 K) in the bulk of the alloy.     

Narrow linewidth light source for an ultraviolet optical frequency standard

We report an ultra-narrow linewidth light source applicable for a frequency standard in the ultraviolet. The laser is a Nd:YAG laser that emits at 946 nm with 300-mW output power. It is locked to a high-finesse cavity. The minimum Allan deviation is 1.3×10^-14 for an integration time of 1 s, which corresponds to a laser linewidth of 2.8 Hz. The cavity drift is measured by a frequency comb and a single-ion spectrum for different time scales. In order to investigate broadening mechanisms due to the fiber transport and doubling systems, the laser light is frequency doubled with two independent systems and compared. The measured minimum beat-note between the two laser fields is less than 1 Hz. By carrying out a high-resolution scan on a trapped single indium ion, we observe a linewidth of 260 Hz on the ion clock transition. Possible reasons for the broadening effects are discussed. PACS 42.55.Xi; 42.62.Eh; 42.65.Ky     

Saturated absorption linewidth: Influence of the source frequency noise

The effect of the source FM noise on the lineshape in sub-Doppler saturation spectroscopy is examined both theoretically and experimentally. We show that the line profile is simply given by the convolution of the homogeneous profile with an effective spectrum, depending on the relative values of the sample relaxation time and of the source frequency correlation time but not departing significantly from the source field power spectrum in the usual cases. This result is well supported by a millimeter wave experiment involving a nearly perfect source, frequency modulated by a Gaussian noise.     

Delay self-heterodyne measurement of narrow linewidth laser frequency drift characteristic

Resonator integrated optic gyro (RIOG), which employs narrow linewidth laser, is a high-accuracy inertial rotation sensor based on the Sagnac effect. The performance of RIOG is greatly affected by the frequency drift of narrow linewidth laser. A simple, effective method to measure the relative frequency drift of narrow linewidth laser based on delayed self-heterodyne technique is proposed in this paper. The measurement range and sensitivity can easily be satisfied by setting the length difference of the fiber segments between two interferometer arms. The relationship between the length difference and the frequency drift is derived based on the given principle of measuring the relative frequency drift. Then the laser frequency drift measuring setup is established and the experiment results demonstrate that a center frequency drift rate is less than 2 MHz/6.7 s under the room-temperature. Moreover, the measuring setup is applied to test the modulation coefficient of piezoelectric-transducer (PZT), and the modulation coefficient of 9.62 MHz/V is obtained, which satisfies the requirements of RIOG closed-loop operation.     

Properties of a two-dimensional semimetal in a strong magnetic field

A system of two-dimensional electrons and holes ha s been investigated in a strong magnetic field, when it is sufficient to take into account only the ground Landau level. It has been shown that the interaction of electrons and holes can lead to an ordered state. In this problem, the exchange interaction in electron and hole subsystems is significant. The following two cases have been considered: (a) there are one electron and one hole valleys, and at some magnetic field strength, there exists an ordered state, as in an excitonic insulator; and (b) there exist one electron and two equivalent hole valleys (as in the experiment performed by Kvon et al. [1]), and the hole system has an ordered state of the Stoner ferromagnetic type in a specific range of magnetic field strengths. The spectra of elementary excitations of the Bose and Fermi types have been obtained. The Fermi excitations have a gap in the energy spectrum, whereas the Bose excitations in the ordered states begin with zero (to these excitations there corresponds an electric dipole moment). The self-consistent field approximation has been used, which is exact when the numbers of electrons and holes are equal to each other.     

太赫兹表面等离激元共振传感器

对通过棱镜耦合的太赫兹表面等离激元共振传感器的工作特性进行了理论分析.此类器件在可见光波段工作时,在由样品折射率、金属膜层性质和厚度决定的共振角度下会出现一个反射极小峰;但工作在太赫兹频率时,表面等离激元共振现象表现为一个反射增强的尖峰,而且这一共振角度与棱镜和样品的折射率之间存在一个简单的对应关系,并不依赖于棱镜所镀...     

Long-term frequency stability and linewidth properties of continuous-wave pump-resonant optical parametric oscillators

We present a frequency stability and linewidth analysis of two different setups of continuous-wave pump and signal-resonant optical parametric oscillators (pump resonant, singly resonant OPO, PR-SRO). Both designs, a common-cavity and a dual-cavity version, utilize a frequency-stable and narrow-linewidth pump laser and are stabilized without using an external reference. A long-term frequency stability better than ±30 MHz is reached over more than 30 minutes for both designs. The frequency jitter on a one-second time-scale is 56 kHz for the common-cavity PR-SRO and about 10 MHz for the dual-cavity PR-SRO. The short-term linewidths were measured using an external high-finesse cavity and are (9±2)kHz and (6±1)kHz in 20 s, respectively. To our knowledge, these are the lowest values demonstrated so far for a widely continuously wavelength-tunable all-solid-state laser source. PACS 42.65.Yj; 42.72.Ai; 42.62.Fi