Large Frequency Shift Research Articles

Stimulated Raman scattering of light in suspension of diamond microparticles in ethanol and in water.

The spectra of stimulated Raman scattering of light in ethanol and in water suspensions containing diamond microparticles with sizes 0.2-0.3μm were investigated. An excitation radiation source was a pulsed ruby laser with a generation wavelength λ0=694.3nm, a pulse duration τp≈20ns, a maximum beam energy of Emax=0.6J, a spectral width Δν=0.015cm-1, and a beam divergence 3.5·10-4rad. For the first time, the observation of stimulated Raman scattering of light at a boson peak in suspension of diamonds microcrystals with close sizes (0.2-0.3μm) in a liquid is reported. The corresponding spectra were recorded using a Fabry-Perot interferometer. In this case, the frequency shift of the stimulated Stokes Raman scattering depended on the size of the diamond microparticles introduced into the liquid and amounted to ~1cm-1. In addition, stimulated Raman scattering by a fundamental optical mode with a frequency shift ν=1331cm-1 was observed. In this case, the Raman spectra were recorded using a small-sized spectrometer with a multi-element receiver, detecting radiation in the range of 200-1000nm. At a sufficiently high intensity of the exciting radiation, the Stokes and anti-Stokes satellites were simultaneously present in the spectrum of stimulated Raman scattering. The obtained results on stimulated scattering of diamond microparticles in liquids are of interest for estimating the sizes of microcrystals from scattering spectra at a boson peak, as well as for creating a frequency comb of emitters based on stimulated Raman scattering with a large frequency shift.

Quantum Versus Classical Switching Dynamics of Driven Dissipative Kerr Resonators

We report a first-principles study of the driven dissipative dynamics for Kerr oscillators in the mesoscopic regime. This regime is characterized by large Kerr nonlinearity, realized here using the nonlinear kinetic inductance of a large array of Josephson junctions. The experimentally measured nonlinear resonance lineshapes of the junction array modes show significant deviations from steady-state numerical predictions, and necessitate time-dependent numerical simulations indicative of strong measurement-induced dephasing in the system arising from the large cross-Kerr effect between array modes. Analytical and numerical calculations of switching rate corroborate this by showing the emergence of a slow time scale, which is much longer than the linear decay rate and is set by fluctuation-induced switching times in the bistable regime. Furthermore, our analysis shows that the usual quantum-activated escape treatment is inadequate for prediction of the switching rates at large frequency shifts caused by strong nonlinearities, necessitating a quantum treatment that utilizes the full system Liouvillian. Based on our analysis, we identify a universal crossover parameter that delineates the regimes of validity of semiclassical and quantum descriptions, respectively. Our work shows how dynamical switching effects in strongly nonlinear systems provide a platform to study quantum-to-classical transitions.

A parametric study of an unbalanced Jeffcott rotor supported by a rolling-element bearing

Rolling-element bearings are widely used in industrial rotating machines, and hence there is a strong need to accurately predict their influence on the response of such systems. However, this can be challenging due to an interaction between the dynamics of the rotor and the bearing nonlinearities, and it becomes difficult to provide a physical explanation for the nonlinear response. A novel approach, combining a Jeffcott rotor supported by a detailed bearing model with the generalised harmonic balance method, is presented, enabling an in-depth study of the complex rotor–stator interaction. This allows the quasi-periodic response of the rotor, due to variable compliance, to be captured, and the impact of clearance, ring and stator compliance, and centrifugal loading of the bearing on the response to be investigated. A strongly nonlinear response was observed due to the bearing, leading to large shifts in frequency as the excitation amplitude was increased, and the emergence of stable and unstable operating regions. The variable compliance effect generated sub-synchronous forcing, which led to sub-resonances when the ball pass frequency coincided with the frequency of one of the modes. Radial clearance in the bearing had by far the largest influence on the unbalance response, the self-excitation due to variable compliance, and the stability. Introducing outer ring compliance was found to slightly soften the system, and centrifugal loading on the bearing elements marginally increased the system’s region of instability, but neither of these effects had a significant impact on the response for the investigated bearing. When the bearing was mounted on a sufficiently compliant stator, the system was found to behave linearly.

Effects of temperature and humidity on the performance of a PECH polymer coated SAW sensor.

The influences of environment, such as temperature, humidity and interfering gases, on the performance of a surface acoustic wave (SAW) sensor in the detection of 2-chloroethyl ethyl sulfide (CEES) were invested. The 150 MHz SAW dual delay lines were used, coated with a poly(epichlorohydrin) (PECH) thin layer, and CEES was detected under different concentrations. Linear correlation between the frequency-shift and the exposure time of the sensor to CEES could be observed, and the limit of CEES could be detected as low as 1.5 mg m−3. Under different temperature (0–50 C°) and humidity (30–80% RH) conditions, CEES was detected by the fabricated SAW sensor coated with PECH, the frequency shifts were measured and the performance of the sensor was evaluated. The results proved that temperature and humidity were the most important factors to influence the performance of SAW sensors; with the decreasing of temperature and the increasing of humidity, there would be larger frequency shifts. In the interference experiments, it was found that most gases existing in the environment in high concentrations would not influence the detection of CEES. Then, the SAW sensor having been fabricated was kept under the conditions of 25 °C and 35% RH for 18 months to further verify the quality, and CEES was detected every so many months. It proved that the performance of the sensor would decrease about 16.39% after 18 months. Although it reflected the attenuation of the sensor to some extent, the sensor was still in good condition. Additionally, the related mechanisms were also discussed.

Chiral Self Recognition: Interactions in Propylene Oxide Complexes.

We elucidate the subtle energetic effects that give rise to chiral recognition in the propylene oxide dimer. Specifically, we investigate six homochiral (RRx) and six heterochiral (RSx) structures of this complex, with the RRn-RSn pair sharing the same pattern of weak O···H-C hydrogen bonds but subtly differing in energy due to chiral effects. The interaction energies for the 12 structures are computed at various levels of electronic structure theory and basis set up to the complete basis set limit of the coupled-cluster approach with single, double, and perturbative triple excitations (CCSD(T)). These benchmark interaction energies are compared to the results of various approximate approaches, both density functional theory-based and wave function-based. We find that while the RRn-RSn diastereomeric energy differences exhibit a great deal of error cancellation between the individual interaction energies, most approximate methods have a hard time even reproducing the correct signs of these differences consistently. The origins of the RRn-RSn differences are elucidated by several symmetry-adapted perturbation theory (SAPT) analyses ranging from ordinary intermolecular SAPT to a functional-group SAPT (F-SAPT) decomposition of direct and indirect H → CH3 substitution effects leading from achiral ethylene oxide complexes to chiral propylene oxide ones. It is shown that the largest diastereomeric energy differences are correlated to the variations in the electrostatic and dispersion SAPT contributions. Finally, the effect of chiral interactions on the vibrational frequencies of a propylene oxide molecule is investigated, showing that the interaction results in largest frequency shifts, splittings, and chiral discrimination effects in the lowest, torsional vibrational mode of the noninteracting monomer.

Digital ammonia gas sensor based on quartz resonator tuned by interdigital electrode coated with polyaniline film

Abstract This paper reported an ammonia gas sensor which was constructed by an interdigital electrode (IDE) coated with PANI thin film connected to quartz resonator in series. The sensor could convert concentration change of ammonia into frequency shift of the quartz resonator through the frequency tuning effect of IDE. Test result showed that the digital ammonia gas sensor exhibited a large frequency shift approximately 1500 Hz in ammonia concentration range of 20–1200 ppm, namely the proposed sensor showed higher frequency change compared with the majority of QCM ammonia sensors. The experiment suggested that the resistance of IDE coated with PANI film increased and meanwhile its capacitance decreased with increasing of ammonia gas concentration. Simulation on Butterworth-van Dyke (BVD) circuit of the sensor revealed that the capacitance of IDE coated with PANI played a major role in tuning of the quartz resonator although the capacitance changed little, while the resistance tuning effect was relatively weak. Compared with the traditional QCM gas sensors, the proposed sensor had a very fast response speed and a good anti-interference ability to pollutants and electromagnetic fields due to encapsulation of quartz crystal.

Thermally Reconfigurable Meta-Optics

Metasurfaces are two-dimensional nanostructures that allow unprecedented control of light through engineering the amplitude, phase, and polarization across meta-atom resonators. Adding tunability to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, tunable metalenses, and reconfigurable meta-holograms, to name a few. We present here high-index meta-atoms, resonators, and metasurfaces reconfigured by thermal effects, across the near to mid-infrared spectral ranges. We study thermal tunability in group IV and group IV–VI semiconductors, as well as in phase-transition materials, and demonstrate large dynamic resonance frequency shifts accompanied by significant amplitude and phase modulation in metasurfaces and resonators. We highlight the importance of high-Q resonances along with peak performance of thermal and thermo-optic effects, for efficient and practical reconfigurable devices. This paper paves the way to efficient high-Q reconfigurable and active infrared metadevices.

Giant Nonlinear AlGaAs-Doped Glass Photonic Crystal Fibers for Efficient Soliton Generation at Femtojoule Energy

In this paper, a unique semiconductor-doped glass photonic crystal fiber has been designed, which is suitable for soliton propagation at femto-Joule energy. The fiber promises to yield low and uniform anomalous dispersion profile and very large optical nonlinearities $\text{25 211 W}^{ - 1} {\text{km}}^{ - 1}$ at telecommunication wavelength, and, thus, facilitating soliton formation at ultralow energy. The observed magnitude of nonlinearity is the highest reported ever till date in AlGaAs-doped glass. The soliton dynamics has been investigated taking into account of higher order dispersions and nonlinearities. Propagating solitons breadth and experience large frequency shift, this decrease with the increase in the initial pulse width and increase with the increase in pulse energy. Temporal width of solitons oscillates, the frequency and amplitude of oscillations increase with the increase in the value of pulse energy.

Reconfigurable microwave properties in C-, L- and S-shaped nanomagnets

Dynamic responses of magnetic nanostructures exist in the GHz frequency range and therefore offer excellent opportunities to miniaturize microwave devices. Here, we have demonstrated C-, L- and S-shaped nanomagnetic structures which enable reconfigurable microwave properties. Magnetic and microwave properties have been studied utilizing micromagnetic simulations. We have obtained two different magnetic remanent states for all the samples by using a simple field initialization process. Different remanent states are associated with distinct magnetization dynamic properties which can be tuned using a magnetic field pulse of nanosecond width. Remarkably large frequency shifts have been observed between the two different magnetic remanent states. Tunable microwave properties relies on the strong dipolar field variations—the effect of which have been shown systematically in all spatial directions in strategically designed sample geometries such as single layer arrays, isolated multilayers and networks of multilayers. The results have potential implications for the realization of ultra-low-power and ultrafast microwave devices.

Megawatt solitons generated above 2000 nm in Bragg fibers

Solitonic effects, including multi-solitonic fission and subsequent self-frequency shift, are used to tailor ultrashort (sub-100 fs) pulses with carrier wavelength broadly tunable in spectral regions between fixed laser lines. Although high-energy pulses can be obtained in stiff waveguides, the benefit of pulse delivery through bends is lost. Here, we report on the generation, sustained propagation, and large frequency shift of megawatt-class pulses in all-silica antiresonant fibers with ultra-large mode area. We designed and fabricated a flexible fiber with a 2710 μm2 effective mode area and a 10 cm critical bend radius. When pumped by a sub-picosecond thulium-doped fiber-based chirped pulse amplifier, the fiber delivers 90 fs pulses at 2220 nm with a 2.8 MW peak power. The system might be used to drive high-order harmonic generation in solids.

Raman Scattering in LiOH and LiOD Polycrystals

We have studied spontaneous and stimulated Raman spectra of polycrystalline LiOH and LiOD. The observed spontaneous Raman spectra contain low-frequency high-quality-factor lattice modes corresponding to translational and librational oscillations of the ions. The stimulated Raman spectrum has been found to contain several Stokes and anti-Stokes satellites with a large frequency shift.

Dual-wavelength terahertz sensing based on anisotropic Fano resonance metamaterials.

Higher order Fano resonance metamaterials provide a desirable platform for biosensing applications. In this work we exhibit higher order Fano modes by designing an elliptical metallic ring. The simulation results show that for Fano resonant metamaterials, the higher order modes lead to improved sensitivity to refractive index change and larger frequency shifts. Numerically, the sensitivity of dip A (quadrupole mode) is 112GHz/RIU, whereas the sensitivity of dip B (octupole mode) is 234GHz/RIU, over 2 times that of dip A. According to our experimental results, the Fano resonant frequencies of dip A and dip B exhibit redshift as the concentration of the anti-cancer drug methotrexate decreases from 120 to 90μM, with the cell analyte concentration of A549 cells at 5×105 cell/ml. For dip A (quadrupole mode), there is a frequency shift of 0.84GHz for drug concentration of 120μM and a frequency shift of 22GHz for a 90μM drug-treated sample. For dip B (octupole mode), there is a frequency shift of 6.767GHz for the drug concentration of 120μM treated sample and a frequency shift of 51.815GHz for the drug concentration of 90μM treated sample. Furthermore, the frequency shift of dip A is always smaller than that of dip B for both 90μM and 120μM drug concentrations. Such phenomena indicate that dip B is much more sensitive than dip A. The enhanced sensitivity of higher order Fano metamaterials makes it possible to realize high-performance terahertz sensing for biomedical applications.

Colloidal quantum dot-based surface acoustic wave sensors for NO2-sensing behavior

Surface acoustic wave (SAW) sensors have great advantages in real-time and in-situ gas detection due to their wireless and passive characteristics. Using nanostructured sensing materials to enhance the SAW sensor’s responses has become a research focus in recent years. In this paper, solution-processed PbS colloidal quantum dots (CQDs) were integrated into quartz SAW devices for enhancing the performance of NO2 detection operated at room temperature. The PbS CQDs were directly spin-coated onto ST-cut quartz SAW delay lines, followed by a ligand exchange treatment using Pb(NO3)2. Upon exposure to 10 ppm of NO2 gas, the sensor coated with untreated PbS CQDs showed response and recovery times of 487 s and 302 s, and a negative frequency shift of −2.2 kHz, mainly due to the mass loading effect caused by the absorption of NO2 gas on the surface of the dense CQD film. Whereas the Pb(NO3)2-treated sensor showed fast response and recovery times of 45 s and 58 s, and a large positive frequency shift of 9.8 kHz, which might be attributed to the trapping of NO2 molecules in the porous structure and thus making the film stiffer. Moreover, the Pb(NO3)2-treated sensor showed good stability and selectivity at room temperature.

Tailoring coupling between light and spin waves with dual photonic–magnonic resonant layered structures

We report on judiciously designed stratified periodic structures of magnetic dielectric materials with a localized defect layer, which are able to concurrently confine light and spin waves in the same ultra-small defect region for a long time period, thus resulting in enhanced photon–magnon interaction and large dynamic optical frequency shift. Our results for a specific realization of such a one-dimensional, so-called photomagnonic, crystal magnetized at saturation perpendicular to the interfaces, obtained by means of rigorous calculations using scattering-matrix techniques, show that the inherently weak coupling between visible/near-infrared light and GHz-frequency spin waves can be greatly increased leading to strong modulation of the optical field through multi-magnon exchange mechanisms. Such novel multifunctional composite materials offer a promising platform for tailoring light–spin-wave coupling in view of fast and energy-efficient spin-optical information processing applications.

Effect of segment length modification on localized modes in Cantor bar microstrip lines

We investigated the impurity modes in a one-dimensional fractal called Cantor bar by modifying the central and side segment lengths of the microstrip lines to control the propagation properties of the microwaves. It was confirmed, using a vector network analyzer, that there exists several localized modes in the photonic gap regions in the third-stage Cantor bar with self-similar patterns. By simulating the electrical current using the method of moments, the microwaves were found to localize in either the central segment area or in both the end areas of the fractal pattern. The length modification of the segment where the microwave is localized led to large frequency shifts of the localized modes and hardly influenced the gap region. The quality factors of the modes localized in the central area are quite affected by the length modifications of both the first and second segments.

New insights into adaptation and population structure of cork oak using genotyping by sequencing.

Species respond to global climatic changes in a local context. Understanding this process, including its speed and intensity, is paramount due to the pace at which such changes are currently occurring. Tree species are particularly interesting to study in this regard due to their long generation times, sedentarism, and ecological and economic importance. Quercus suber L. is an evergreen forest tree species of the Fagaceae family with an essentially Western Mediterranean distribution. Despite frequent assessments of the species' evolutionary history, large-scale genetic studies have mostly relied on plastidial markers, whereas nuclear markers have been used on studies with locally focused sampling strategies. In this work, "Genotyping by sequencing" is used to derive 1,996 single nucleotide polymorphism markers to assess the species' evolutionary history from a nuclear DNA perspective, gain insights into how local adaptation is shaping the species' genetic background, and to forecast how Q.suber may respond to global climatic changes from a genetic perspective. Results reveal (a) an essentially unstructured species, where (b) a balance between gene flow and local adaptation keeps the species' gene pool somewhat homogeneous across its distribution, but still allowing (c) variation clines for the individuals to cope with local conditions. "Risk of Non-Adaptedness" (RONA) analyses suggest that for the considered variables and most sampled locations, (d) the cork oak should not require large shifts in allele frequencies to survive the predicted climatic changes. Future directions include integrating these results with ecological niche modeling perspectives, improving the RONA methodology, and expanding its use to other species. With the implementation presented in this work, the RONA can now also be easily assessed for other organisms.

Robust retrospective frequency and phase correction for single-voxel MR spectroscopy.

Subject motion and static field (B0 ) drift are known to reduce the quality of single voxel MR spectroscopy data due to incoherent averaging. Retrospective correction has previously been shown to improve data quality by adjusting the phase and frequency offset of each average to match a reference spectrum. In this work, a new method (RATS) is developed to be tolerant to large frequency shifts (>7Hz) and baseline instability resulting from inconsistent water suppression. In contrast to previous approaches, the variable-projection method and baseline fitting is incorporated into the correction procedure to improve robustness to fluctuating baseline signals and optimization instability. RATS is compared to an alternative method, based on time-domain spectral registration (TDSR), using simulated data to model frequency, phase, and baseline instability. In addition, a J-difference edited glutathione in-vivo dataset is processed using both approaches and compared. RATS offers improved accuracy and stability for large frequency shifts and unstable baselines. Reduced subtraction artifacts are demonstrated for glutathione edited MRS when using RATS, compared with uncorrected or TDSR corrected spectra. The RATS algorithm has been shown to provide accurate retrospective correction of SVS MRS data in the presence of large frequency shifts and baseline instability. The method is rapid, generic and therefore readily incorporated into MRS processing pipelines to improve lineshape, SNR, and aid quality assessment.

Comparative study on calculated terahertz absorption spectra of different heterostructure materials with external magnetic field

Room temperature operation and frequency tunability are attractive advantages of terahertz (THz) detectors based on the two-dimensional electron gas (2DEG) in the heterostructure material with external magnetic field. This work compared absorption spectra of four typical heterostructure materials (AlGaN/GaN, InAlN/GaN, AlGaAs/GaAs and SiGe/Si) with the nonlocal magnetoconductivity model at ambient and cryogenic temperatures in the frequency range 0–5 THz. The GaN based materials have the highest absorption amplitude, while the AlGaAs/GaAs material owns the largest frequency shift as the magnetic field increases up to 10 tesla, although superconducting magnets at cryogenic temperature are usually employed to provide that high magnetic field. The numerical results showed that the absorption properties (amplitude and frequency) could be further optimized by other parameters, such as the period and filling factor of the grating coupler, and the barrier thickness.

Brillouin optical time-domain analyzer with frequency shift keying probe

A Brillouin optical time-domain analysis (BOTDA) technique for enhancing the probe power to +5 dBm is proposed and demonstrated, which is based on a conventional dual sideband probe setup, but the probe waves are modulated by a frequency shift keying signal. The pump distortion is compensated in the time domain with this technique. By employing a 105-km sensing fiber, this technique is experimentally validated with 2-m spatial resolution. Furthermore, another experiment is designed to show the good tolerance for the sensing fibers combined with large Brillouin frequency shift (BFS) difference, as is demonstrated in a 50-km-long sensing fiber consisting of two segments with large BFS difference (200 MHz).

Photodissociation Spectroscopy of Cold Protonated Synephrine: Surprising Differences between IR-UV Hole-Burning and IR Photodissociation Spectroscopy of the O-H and N-H Modes.

We report the UV and IR photofragmentation spectroscopies of protonated synephrine in a cryogenically cooled Paul trap. Single (UV or IR) and double (UV-UV and IR-UV) resonance spectroscopies have been performed and compared to quantum chemistry calculations, allowing the assignment of the lowest-energy conformer with two rotamers depending on the orientation of the phenol hydroxyl (OH) group. The IR-UV hole burning spectrum exhibits the four expected vibrational modes in the 3 μm region, i.e., the phenol OH, Cβ-OH, and two NH2+ stretches. The striking difference is that, among these modes, only the free phenol OH mode is active through IRPD. The protonated amino group acts as a proton donor in the internal hydrogen bond and displays large frequency shifts upon isomerization expected during the multiphoton absorption process, leading to the so-called IRMPD transparency. More interestingly, while the Cβ-OH is a proton acceptor group with moderate frequency shift for the different conformations, this mode is still inactive through IRPD.