Pump Wave Research Articles

All-Optical Method of Determining Laser Power from the Photomechanical Effect

A method to determine the power of a continuous wave laser from photothermal heating of a poly(dimethyl siloxane) film is reported. The base was doped with oil red O and cured on a surface relief grating. The grating period was shown to increase proportional to the temperature by monitoring the decrease in diffraction angle of a probe beam. A 10s illumination period of a continuous wave (CW) pump beam absorbed by the film increased the film’s temperature, which resulted in a local strain that could be modeled using the two-dimensional heat kernel. The amplitude of the transient response was found to be linearly correlated with the pump laser power.

Dual Optical Frequency Comb Generation with Dual Cascaded Difference Frequency Generation

In this work, we propose a novel dual optical frequency comb (DOFC) generation scheme based on dual cascaded difference frequency generation (DCDFG). Feasible designs are introduced that enable the two sets of cascaded optical waves, initially generated by DCDFG in an aperiodically periodically poled lithium niobate (APPLN) crystal with a pump wave and two signal waves, then transferred to high-order Stokes waves by oscillations of cascaded Stokes waves and the optimization of phase mismatching of each-order DCDFG; finally, a DOFC was constructed. We demonstrate a high-performance DOFC with characteristics of high repetition frequency difference, tunable repetition frequency difference, high flatness, and a tunable spectral distribution range by providing a theoretical framework. We argue that the scheme proposed in this work is promising for achieving a high-quality DOFC.

Particle-in-cell simulations on parametric instability of the lower hybrid wave

Lower hybrid (LH) wave is an effective tool for current drive (CD) on tokamak devices. Parametric instability (PI) has always been a troubling phenomenon decreasing the lower hybrid current drive efficiency. In this work, the PI behavior of the LH waves for plasma parameters on the Experimental Advanced Superconducting Tokamak is investigated via first-principle simulation with a two-dimensional full-particle-in-cell method. The PI processes where an LH pump wave decays into another LH sideband and a low-frequency mode [ion sound quasi-mode (ISQM) or ion cyclotron quasi-mode (ICQM)] are observed in simulations. The ICQM-type and ISQM-type decay channels dominate, respectively, in the high- and low-plasma regimes while appearing simultaneously in the intermediate regime, which agrees well with the theoretical prediction by solving the parametric dispersion relation. In addition, for both the decay channels, their LH sidebands are excited with a wide range of parallel refractive index N∥ up to 30.0, which can resonantly interact with thermal electrons. The resulting electron heating can be enhanced due to overlap of resonances between the electrons and sidebands. Such electron heating not only dissipates the wave energy in the edge plasma but produces a significant portion of fast electrons, which may seriously affect tokamak discharges. The ion cyclotron heating due to the ICQMs is also observed in simulations.

Four-wave mixing on thermal nonlinearity with feedback for signal or object waves

The coincidence of the amplitude reflection coefficients, half-widths of the spatial frequencies bands of a four-wave radiation converter on thermal nonlinearity with feedback for signal or object waves has been shown at equal pump waves intensity. The dependence of the amplitude reflection coefficient, spatial selectivity of the four-wave radiation converter on thermal nonlinearity on the pump waves intensity has been analyzed. An increase in the half-width of the spatial frequency band is observed with an increase in the pump waves intensity at the compensation for the phase shift arising as a result of the propagation of the pump waves in the medium. There is a threshold value of the pump waves intensity, above which the value of the amplitude reflection coefficient of the four-wave converter with feedback for signal or object waves, is less than in the absence of feedback.

Influence of self-focused high power Cosh-Gaussian beam on second harmonic generation in cold quantum plasma

The objective of present work is to investigate influence of self-focused high power Cosh-Gaussian (ChG) beam on second harmonic generation (SHG) in cold quantum plasma (CQP). WKB and Paraxial approximations are utilized for acquiring 2nd order differential equation representing propagation characteristics of ChG beam with normalized propagation distance. The modification in dielectric function of plasma is observed on account of relativistic nonlinearity causing self-focusing of ChG beam. The density gradients are produced in transverse direction. These density gradients cause electron plasma wave (EPW) excitation at main wave frequency. Further, the nonlinear interaction between pump wave and excited EPW produces 2nd harmonics in plasma. We have performed numerical simulations for exploring impact of various laser & plasma parameters on beam waist of ChG beam and conversion efficiency of 2nd harmonics. We have also made the comparison of given work with classical relativistic plasma (CRP) regime.

Disturbances of electron density in the high latitude upper (F-region) ionosphere induced by X-mode HF pump waves from EISCAT UHF radar observations

The paper presents experimental results concerning disturbances of electron density in the high latitude ionosphere F-region, induced by powerfulHF radio waves (pump waves) with extraordinary (X-mode) polarization. The experiments were carried out at the EISCAT/Heating facility at Tromsø, Norway. The EISCAT UHF incoherent scatter radar (ISR), running at 930 MHz, co-located with a heating facility, was used to detect the disturbances of electron density. In the course of the experiments, the X-mode HF pump waves radiated into the F-region towards the magnetic zenith at different pump frequencies and ratios of the pump frequency to the critical frequency of the F2 layer.The effective radiated power was ERP = 360–820 MW. An increase in electron densities was found in a wide altitude range, giving rise to field-aligned ducts with enhanced electron density. The features and behavior of the ducts were investigated. It was revealed that the ducts are formed under quiet background geophysical conditions in a wide altitude range up to the upper altitude limit of EISCAT ISR measurements, when the pump frequencies were both below and above the critical frequency of the F2 layer (fH ≤ foF2 or fH > foF2). A plausible formation mechanism of the ducts is discussed.

High-order harmonic generation in three-dimensional Weyl semimetals with broken time-reversal symmetry

In this paper the nonlinear interaction of a Weyl semimetal (WSM) with a strong driving electromagnetic wave field is investigated. In the scope of the structure-gauge-invariant low-energy nonlinear electrodynamic theory, the polarization-resolved high-order harmonic generation spectra in the WSM with broken time-reversal symmetry are analyzed. The results obtained show that the spectra in the WSM are completely different compared to the two-dimensional graphene case. In particular, at the noncollinear arrangement of the electric and Weyl node momentum separation vectors, anomalous harmonics are generated which are polarized perpendicular to the pump wave electric field. The intensities of anomalous harmonics are quadratically dependent on the momentum space separation of the Weyl nodes. If the right and the left Weyl fermions are merged, we have a four-component trivial massless Dirac fermion and, as a consequence, the anomalous harmonics vanish. In contrast to the anomalous harmonics, the intensities of normal harmonics do not depend on the Weyl nodes' momentum separation vector and the harmonics spectra resemble the picture for a massless three-dimensional Dirac fermion.

Discriminative strain and temperature sensing using a ring-hyperbolic tangent fiber sensor.

Brillouin fiber sensors have demonstrated strong capability in discriminative and high-sensitivity multiparameter measurements. In this study, we proposed and numerically investigated novel ring core fiber-based stimulated Brillouin scattering for the simultaneous measurement of temperature and strain. The novel fiber, referred to as ring hyperbolic tangent (R-HTAN) fiber, is characterized by a shape parameter (α) that controls the optical refractive index and longitudinal acoustic velocity profiles. Numerical modal simulations indicated that the Brillouin gain spectrum contained multiple widely spaced and high-gain peaks, which were attributed to the strong interaction between the optical linearly polarized mode (i.e., LP0,1 as a pump wave) and multiple high-order longitudinal acoustic modes. The designed R-HTAN fiber enabled the discriminative sensing of temperature and strain with levels that clearly surpassed values recently reported in the literature. In case of straight R-HTAN fiber (α = 0), the maximum C(α=0)T and C(α=0)ε are 1.928 MHz/ ∘C and 0.087 MHz, respectively. In case of graded R-HTAN fiber (α = 1), the maximum C(α=1)T and C(α=1)ε are 1.872 MHz/ ∘C and 0.0842 MHz/μɛ, respectively. The errors associated with temperature measurements (maximum δT(α=0) = 0.0846 ∘C and maximum δT(α=1) = 7.4184 ∘C) and strain measurements (maximum δɛ(α=0) = 0.7250 μɛ and maximum δɛ(α=1) = 7.4184 μɛ) demonstrated that the proposed fiber could be a promising candidate for next-generation Brillouin sensing systems for enabling temperature and strain discrimination.

Quantification of the effect of pump wave amplitude on crack breathing for the Nonlinear Coda Wave Interferometry

In civil engineering, an emerging ultrasonic approach based on Code Wave Interferometry (CWI), called Nonlinear Coda Wave Interferometry (NCWI) has been developed to detect microcracks in cementitious materials that cannot be detectedby conventional ultrasonic methods. NCWI uses a high amplitude low frequency (LF) nonlinear pump wave to generate a nonlinear clapping effect at microcracks that can be detected by a high frequency (HF) probe wave. The imaging of cracks inside heterougeneous materials using NCWI requires the inversion technique, which is constitued by model space and data space, in which conatains model parameters and data parameters respectively. In the frame of inversion with NCWI, the model parameter used is the scatetring cross section of a crack sigmaD, and the experimental parameter is the decorrelation coefficient Kd. Knowing that sigmaD depends on the pump wave amplitude. Therefore, in order to introduce NCWI in inversion, the relationship between the pump wave and sigmaD is needed, which is the goal of this study. The dynamic pump wave generates clapping effect at crack tips, the probe wave frequencies are higher than the pump waves’ by an order of magnitude, hence the effect of pump wave on the coda wave is rather averaged. Previous study showed that this clapping effect is equivalent to a single crack length change dL, dL can be related to an equivalent static stress sigma0 which produces the same dL in quasi-static regime, which is equivalent to the dynamic pump wave. Therefore, a relation can be established between sigma0 and sigmaD. This introduces NCWI into the inverison. Then, the theoretical estimation of Kd can be achieved by the simulation of NCWI using 2D Spectral Element Method (SEM2D), combining with the relationship between sigma0 and sigmaD, which can be used later on in the inversion for the crack imaging.

Impacts of strong positive Indian Ocean Dipole on the generation of the Great Whirl

The Great Whirl (GW) is an anticyclonic mesoscale eddy, forming periodically in the tropical western Indian Ocean. The lifespan of the GW exhibits a marked interannual variability, which has a late generation time and short lifetime due to the abnormal local wind field in a strong positive IOD year. The anomalous northeasterly wind inputs positive wind stress curl into the ocean, which is not conducive to establishing a stable anticyclonic circulation at the early stage of GW formation. In addition, oceanic Rossby waves exert impacts on the GW generation. The abnormal Rossby waves account for the earlier generation time of the GW in 2019 despite the unfavorable local wind field. This study identifies the atypical lifespan of the GW associated with a positive IOD event and reveals the contribution of local Ekman pumping and Rossby wave propagation.

Phase complementarity and magnification effect of optical pump rogue wave and Stokes rogue wave in a transient stimulated Raman scattering system

In this article, we study the phase complementarity and magnification effect of the optical pump wave and Stokes wave in a transient stimulated Raman scattering (TSRS) system. We construct new pump and Stokes rogue wave modulus solutions by applying Darboux transformation method. According to the number and layout of peak and trough, there are three phases for both the pump and Stokes rogue waves. Furthermore, it is novel that there does exist phase complementarity between the pump and Stokes rogue waves. Then, the magnification effect from the pump rogue wave to the Stokes rogue wave is also investigated.

Long-Range High-Spatial-Resolution Distributed Measurement by a Wideband Brillouin Amplification-Boosted BOCDA

Stimulated Brillouin scattering (SBS)-based distributed fiber optic sensing technique has found pervasive applications in measurement of real-world environmental variables. Its sensing capability, however, is affected by the tradeoff between sensing distance and spatial resolution. Herein, we propose and experimentally verify a wideband Brillouin amplification (WBA)-boosted BOCDA to achieve the high spatial resolution sensing in a longer distance. The WBA is generated by exploiting phase-uncorrelated SBS process between pump and probe waves. Through the WBA, the pump pulses at different scanning frequencies are amplified with the same ratio, which brings distortion-free enhancement of Brillouin signals. The signal-enhancement improves the sensing distance of high spatial resolution BOCDA. As a result, without any additional (Raman/Brillouin) amplification devices, a ∼0.46 MHz measurement certainty and a 6 cm spatial resolution are achieved over a ∼40 km sensing range. The proposed method offers a viable solution for the applications that need high-resolution measurement of remote targets.

Nonlinear optical frequency conversion by cascaded difference frequency generation

We propose a nonlinear optical frequency conversion method based on cascaded difference frequency generation. Feasible designs are presented that enable the cascaded optical waves. They are initially generated by cascaded difference frequency generation with two pump waves, then transferred to high-order Stokes waves by optimized cascaded difference frequency generation, and finally congregated at a few spectral lines. We demonstrate wide frequency tuning characteristics and high conversion efficiency characteristics of the nonlinear frequency convertor by providing a theoretical framework. The frequency tuning from 291 THz to 175 THz and energy conversion efficiency exceeding 30% are achieved by numerical calculations. The nonlinear frequency convertor exhibits physics distinctly different from conventional three-wave mixing parametric amplification or difference frequency generation. We argue that the nonlinear frequency convertor based on cascaded difference frequency generation is promising for achieving efficient and robust frequency conversion.

Neutral beam driven ion cyclotron instability of lower hybrid wave in a tokamak plasma

The effect of dust grains on the parametric coupling of neutral beam driven ion–cyclotron wave instability with a lower hybrid pump wave is studied. A high amplitude lower hybrid pump, which is launched into a tokamak for heating purposes in the presence of neutral beam driven ion-cyclotron waves, can excite the parametric coupling involving two lower hybrid sidebands. In a tokamak, the lower hybrid waves result in parametric excitation of the ion-cyclotron mode and quasi-modes near the edge when the electron oscillatory velocity is greater than the sound velocity. This parametric coupling increases the growth rate of instability when the lower sideband wave is resonant. Moreover, the presence of dust grains in the tokamak plasma, their radius, and the number density significantly affect the growth rate of the instability, which in turn can affect the advanced stage operations of a tokamak. The growth rate of parametric instability scales with the amplitude of the pump wave. The growth rate is found to be linearly increased with the dust grain density, but it decreased with increasing size of dust grains, which means large sized dust grains stabilize the instability. The theoretical results explained in the present paper are very helpful in explaining the complexity in the plasma properties of a tokamak due to the dust–plasma interactions, which can diminish the performance of the International Thermonuclear Experimental Reactor due to potential safety issues.

Spatial and temporal characteristics of a four-wave radiation converter with due regard for Earth's gravity field acting on nanoparticles dissolved in a transparent liquid

A theoretical analysis of the dynamics of the spatial spectrum of the object wave in a degenerate four-wave mixing in a transparent solution of nanoparticles in the classical scheme with counterpropagating pump waves is carried out. It is shown that when pump waves propagate orthogonally to the gravity force, a dip arises in the modulus of the spatial spectrum of the object wave, with its half-width nonmonotonically decreasing over time and increasing in the direction of gravity force with increasing radius of the nanoparticles. There is an optimal time over which the half-width of the dip in the direction of the gravity force reaches the lowest value. This time decreases monotonically with increasing nanoparticle radius, as well as with a decrease in the solution thickness.

Zero-field level-crossing resonances in a small low-temperature cesium vapor cell for atomic magnetometry applications

Zero-field level-crossing resonances (LCRs) underlay one of the most robust and simplest techniques in atomic magnetometry. LCR-based miniaturized magnetic field sensors have already found relevant applications in biology and medicine. Such sensors utilize a single circularly polarized light wave to interact with alkali-metal atoms (usually Rb or Cs) and to observe the LCR in a vapor-cell transmission when a transverse magnetic field is scanned around zero value. A high-temperature regime (T ≈ 120 − 160°C) is required to achieve a desirable sensitivity of measurements. It can be a problem for some applications, especially in a multi-channel mode of operation. Here, we consider two spectroscopy techniques that can provide high-contrast and narrow LCRs under a relatively low temperature of the cell (≤60°C). These techniques imply using two light waves: the pump wave to polarize the atoms and the probe one to register the resonance. A cubic glass cell of 5×5×5 mm3 size is used in the experiments. It is filled with cesium vapors and neon as a buffer gas. The results can be used for developing a miniaturized low-power high-sensitivity magnetic field sensor for biomedical applications.

A nonlinear wave-based model to study the magnetic turbulence generation associated with the nonlinear evolution of Kinetic Alfven Wave in laser-produced plasma relevant to laboratory and astrophysical plasmas

A nonlinear wave-based model is introduced to understand the behaviour of the ion-scaled magnetic turbulence in the laser-produced plasmas generated during the high-intensity laser-plasma interaction. The coupled model equations are developed for the pump Kinetic Alfven Wave and the low-frequency Magnetosonic Wave by taking into account the ponderomotive nonlinearity. Numerical simulation is performed using the pseudo-spectral and the finite difference method to solve the model equations. The simulation results illustrate the nonlinear evolution of the pump wave at the early stage, which subsequently becomes turbulent. From the simulation results, the time-averaged turbulent power spectrum has been studied. The observed MHD type and KAW type plasma turbulence in different spatial scale lengths are nearly close to the magnetic turbulence reported in Chatterjee et al.12 experimental results. A semi-analytical method is also given to better understand the nonlinear evolution of the pump wave inside the plasma medium. Such studies of nonlinear wave-based models could be crucial in imitating the astrophysical phenomena by laboratory simulations and understanding the inherent essential physics of magnetic turbulence.

Nonreciprocal acoustic transmission through dynamic multilayer structures

A time Floquet transfer-matrix method for the description of acoustic wave propagation through dynamic stratified structures, modulated by another, low-frequency, pump acoustic wave, is reported. The method is applied to a specific example of a GaAs/AlAs periodic superlattice, subject to a spatiotemporal modulation induced by an evanescent pump wave with frequency in the lowest acoustic band gap of the structure. By means of systematic numerical calculations, we provide compelling evidence for the occurrence of significant nonreciprocal transmission of an acoustic signal with frequency in a high-order acoustic band gap, through inelastic multiple-scattering processes. Our results indicate a promising route to design nonreciprocal acoustic devices.

Enigmas of modulational instability in the zero-gain spectral region: The paradox of large-scale perturbations and the pronounced effect of the rogue-wave peak power saturation

Objective:Despite fifty years of intensive research, the study of modulational instability continues to be a source of new and intriguing problems. The main objective of our study consists in revealing unexpected features of the induced modulational instability that arise at its nonlinear stage. Method:The nonlinear stage of induced modulation instability is investigated by direct computer simulation. Results:Our computer experiments carried out in the so-called zero-gain spectral region, clearly demonstrate the pronounced effect of the rogue-wave peak power saturation. The main quantity that determines both the peak values of rogue waves and their subsequent splitting is the total energy stored in one period of an externally modulated quasi-continuous pump wave. Importance of the results:The significance of the results lies in the possibility of controlling the formation of rogue waves induced by periodic modulation of the pump.

Enlargement of mode size in annealed proton-exchanged periodically-poled MgO doped stoichiometric LiTaO3 waveguide for high power second harmonic generation

Watt-class wavelength conversion is expected by enlarging the mode size of the channel waveguides to dozens of micrometers to avoid optical damage with high-power pump lasers. In this work, uniform periodically-poled (PP) structures in MgO doped stoichiometric LiTaO3 were fabricated by applying voltage with a SiO2 insulation layer. Annealed proton-exchanged waveguides with a full width at 1/e 2 maximum in a width of 43 μm with an in-depth of 28 μm were obtained by proton exchanging for 4 h and thermal diffusion for 75 h. This waveguide can be excited by pump waves with a power of 8.6 W considering the optical damage threshold. Second harmonic generation with a wavelength of 515 nm was conducted in the low power region of about 35 mW to investigate the basic characteristics. Normalized wavelength conversion efficiency in the 15 mm long PP structures was estimated to be 4.3% W−1.