Traditional Pulses Research Articles

Few-femtosecond soft X-ray transient absorption spectroscopy with tuneable DUV-Vis pump pulses

Achieving few-femtosecond resolution for a pump-probe experiment is crucial to measuring the fastest electron dynamics and for creating superpositions of valence states in quantum systems. However, traditional UV-Vis pump pulses cannot achieve few-fs durations and usually operate at fixed wavelengths. Here, we present, to our knowledge, an unprecedented temporal resolution and pump tuneability for UV-Vis-pumped soft X-ray transient absorption spectroscopy. We have combined few-fs deep-UV to visible tuneable pump pulses from resonant dispersive wave emission in hollow capillary fiber with attosecond soft X-ray probe pulses from high harmonic generation. We achieve sub-5-fs time resolution, sub-fs interferometric stability, and continuous tuneability of the pump pulses from 230 to 700 nm. We demonstrate that the pump can initiate an ultrafast photochemical reaction and that the dynamics at different atomic sites can be resolved simultaneously. These capabilities will allow studies of the fastest electronic dynamics in a large range of photochemical, photobiological and photovoltaic reactions.

Supercontinuum generation by nonlinear polarization rotation mode-locked fiber laser with pulse type switchable

We report on the generation of a supercontinuum (SC) by nonlinear polarization-rotating (NPR) mode-locked fiber laser, which includes a pulsed switchable NPR mode-locked fiber laser, an Er-doped fiber amplifier, and high nonlinear fiber (HNLF). In the experiment, by adjusting the polarization controller (PC) angle and pump power, we obtained three different pulses. They are traditional soliton bunch pulses, the coexistence of soliton bunch pulses and square pulses, and multi-longitudinal mode noise like square pulses. All three pulses can generate SC with spectrum width be about of 1000 nm. We fixed the pump power in the laser and observed the influence of amplifier power on the spectrum width and output power of SC. The SC width of soliton bunch pulse reaches 950.9 nm, the SC of soliton bunch pulse and square pulse coexisting pulse is 1009.7 nm, and the SC spectrum width of multi-longitudinal mode noise like square pulse is 887.1 nm. Our results demonstrate the generation of SC with three types of switchable pulses, opening up possibilities for various application requirements.

Theoretical study of discriminative electroporation effect between tumor and normal blood vessels by high-frequency bipolar and traditional monopolar pulses

Theoretical study of discriminative electroporation effect between tumor and normal blood vessels by high-frequency bipolar and traditional monopolar pulses

Triphasic Pulse Stimulation Pattern in Cochlear Implant Users Assessed with Ecap Measure

The rationale for the use of three-phase stimulation for programming the processor of the cochlear implantation system (CI) in patients with deafness is presented. To study the possibilities of using a new type of stimulation, we selected patients after cochlear implantation, with signs of facial nerve stimulation (FNS) in postoperative period. All subjects were previously fitted with an audio processor with individual fitting maps based on traditional biphasic stimulation. The use of three-phase stimulation to prevent FNS is caused by the geometry of the electric current pulses, which allows to reduce the penetrating power of the charge in the tissues and eliminate the effect on the facial nerve, without resorting to reducing the levels of stimulation necessary to create a dynamic range of sound perception. Comparative data of the parameters and the results of audiological testing in 21 patients with symptoms of FNS with traditional (two-phase) and three-phase electrical pulses in the stimulation algorithm of the CI system are presented. The positive effect of three-phase stimulation has been established. The results of the study show a significant increase in sound perception indicators when switching to a three-phase stimulation algorithm.

Pulse optimization for high-precision motional-mode characterization in trapped-ion quantum computers

High-fidelity operation of quantum computers requires precise knowledge of the physical system through characterization. For motion-mediated entanglement generation in trapped ions, it is crucial to have precise knowledge of the motional-mode parameters such as the mode frequencies and the Lamb–Dicke parameters. Unfortunately, the state-of-the-art mode-characterization schemes do not easily render the mode parameters in a sufficiently accurate and efficient fashion for large-scale devices, due to the unwanted excitation of adjacent modes in the frequency space when targeting a single mode, an effect known as the cross-mode coupling. Here, we develop an alternative scheme that leverages the degrees of freedom in pulse design for the characterization experiment such that the effects of the cross-mode coupling is actively silenced. Further, we devise stabilization methods to accurately characterize the Lamb–Dicke parameters even when the mode frequencies are not precisely known due to experimental drifts or characterization inaccuracies. We extensively benchmark our scheme in simulations of a three-ion chain and discuss the parameter regimes in which the shaped pulses significantly outperform the traditional square pulses.

Mainstreaming traditional fruits, vegetables and pulses for nutrition, income, and sustainability in sub-Saharan Africa: the case for Kenya and Ethiopia.

This study documented existing knowledge on traditional fruits, vegetables and pulses in Kenya and Ethiopia. The aim was to identify neglected and underutilized species with high potential for food security, for their economic value and contribution to sustainable agriculture, based on a literature review and confirmation of existing data by local experts. In order of priority, the top 5 fruit species in Kenya are Tamarindus indica L., Adansonia digitata L., Sclerocarya birrea (A.Rich.) Hochst, Balanites aegyptiaca (L.) Delile, and Ziziphus mauritiana Lam., for vegetables are Amaranthus spp., Vigna unguiculata (L.) Walp., Solanum spp., and Cleome gynandra L. Top fruits in Ethiopia are Balanites aegyptiaca (L.) Delile, Ziziphus spina-christi (L.) Desf., Cordeauxia edulis Hemsl., Cordia africana Lam., and Mimusops kummel A. DC., for vegetables are Brassica carinata A. Braun, Cucurbita pepo L., and Amaranthus spp. In both countries, priority pulse species (no ranking) are Phaseolus lunatus L., Sphenostylis stenocarpa (A.Rich.) Harms, Mucuna pruriens (L.) DC., Lablab purpureus (L.) Sweet, and Cajanus cajan (L.) Millsp. Generally, these priority species are good sources of key nutrients known for their inadequate dietary intakes in sub-Saharan Africa, represent a safety net for household income, and contribute positively to ecosystem resilience in existing agricultural systems. Complete, accurate and reliable nutrient composition data are needed to raise consumer awareness about their nutritional and health benefits. Since women play a central role in traditional food systems, their empowerment, and hence resilience, increase the positive impact they can have on the households' dietary diversity. In particular, introducing small-scale processing techniques and marketing strategies could enhance their supply and consumption.

Temporally non-regular patterns of deep brain stimulation (DBS) enhance assessment of evoked potentials while maintaining motor symptom management in Parkinson's disease (PD)

BackgroundTraditional deep brain stimulation (DBS) at fixed regular frequencies (>100 Hz) is effective in treating motor symptoms of Parkinson's disease (PD). Temporally non-regular patterns of DBS are a new parameter space that may help increase efficacy and efficiency. ObjectiveTo compare the effects of temporally non-regular patterns of DBS to traditional regularly-spaced pulses. MethodsWe simultaneously recorded local field potentials (LFP) and monitored motor symptoms (tremor and bradykinesia) in persons with PD during DBS in subthalamic nucleus (STN). We quantified both oscillatory activity and DBS local evoked potentials (DLEPs) from the LFP. ResultsTemporally non-regular patterns were as effective as traditional pulse patterns in modulating motor symptoms, oscillatory activity, and DLEPs. Moreover, one of our novel patterns enabled recording of longer duration DLEPs during clinically effective stimulation. ConclusionsStimulation gaps of 50 ms can be used to increase efficiency and to enable regular assessment of long-duration DLEPs while maintaining effective symptom management. This may be a promising paradigm for closed-loop DBS with biomarker assessment during the gaps.

Cochlear Implant Stimulation Parameters Play a Key Role in Reducing Facial Nerve Stimulation.

A percentage (i.e., 5.6%) of Cochlear Implant (CI) users reportedly experience unwanted facial nerve stimulation (FNS). For some, the effort to control this problem results in changing stimulation parameters, thereby reducing their hearing performance. For others, the only viable solution is to deactivate the CI completely. A growing body of evidence in the form of case reports suggests that undesired FNS can be effectively addressed through re-implantation with an Oticon Medical (OM) Neuro-Zti implant. However, the root of this benefit is still unknown: is it due to surgical adjustments, such as varied array geometries and/or positioning, or does it stem from differences in stimulation parameters and/or grounding? The OM device exhibits two distinct features: (1) unique stimulation parameters, including anodic leading pulses and loudness controlled by pulse duration-not current-resulting in lower overall current amplitudes; and (2) unconventional grounding, including both passive (capacitive) discharge, which creates a pseudo-monophasic pulse shape, and a 'distributed-all-polar' (DAP) grounding scheme, which is thought to reduce current spread. Unfortunately, case reports alone cannot distinguish between surgical factors and these implant-related ones. In this paper, we present a novel follow-up study of two CI subjects who previously experienced FNS before re-implantation with Neuro-Zti implants. We used the Oticon Medical Research Platform (OMRP) to stimulate a single electrode in each subject in two ways: (1) with traditional monopolar biphasic cathodic-first pulses, and (2) with distinct OM clinical stimulation. We progressively increased the stimulation intensity until FNS occurred or the sound became excessively loud. Non-auditory/FNS sensations were observed with the traditional stimulation but not with the OM clinical one. This provides the first direct evidence demonstrating that stimulation parameters and/or grounding-not surgical factors-play a key role in mitigating FNS.

Optogenetic Generation of Neural Firing Patterns with Temporal Shaping of Light Pulses

The fundamental process of information processing and memory formation in the brain is associated with complex neuron firing patterns, which can occur spontaneously or be triggered by sensory inputs. Optogenetics has revolutionized neuroscience by enabling precise manipulation of neuronal activity patterns in specified neural populations using light. However, the light pulses used in optogenetics have been primarily restricted to square waveforms. Here, we present a detailed theoretical analysis of the temporal shaping of light pulses in optogenetic excitation of hippocampal neurons and neocortical fast-spiking interneurons expressed with ultrafast (Chronos), fast (ChR2), and slow (ChRmine) channelrhodopsins. Optogenetic excitation has been studied with light pulses of different temporal shapes that include square, forward-/backward ramps, triangular, left-/right-triangular, Gaussian, left-/right-Gaussian, positive-sinusoidal, and left-/right-positive sinusoidal. Different light shapes result in significantly different photocurrent amplitudes and kinetics, spike-timing, and spontaneous firing rate. For short duration stimulations, left-Gaussian pulse results in larger photocurrent in ChR2 and Chronos than square pulse of the same energy density. Time to peak photocurrent in each opsin is minimum at right-Gaussian pulse. The optimal pulse width to achieve peak photocurrent for non-square pulses is 10 ms for Chronos, and 50 ms for ChR2 and ChRmine. The pulse energy to evoke spike in hippocampal neurons can be minimized on choosing square pulse with Chronos, Gaussian pulse with ChR2, and positive-sinusoidal pulse with ChRmine. The results demonstrate that non-square waveforms generate more naturalistic spiking patterns compared to traditional square pulses. These findings provide valuable insights for the development of new optogenetic strategies to better simulate and manipulate neural activity patterns in the brain, with the potential to improve our understanding of cognitive processes and the treatment of neurological disorders.

Prototype Filter Design for Effectively Suppressing Out-of-Band Radiation in GFDM Systems

In this letter, a design method of a prototype filter for effectively suppressing out-of-band radiation (OOBR) in generalized frequency division multiplexing (GFDM) systems is proposed. A generic model that can suppress out-of-band energy leakage in the frequency-domain is introduced. The function that is solved in this model gives the target prototype filter. By adding several constraints such as the boundary, energy and spectral density energy concentration degree (SDECD) to the objective function, a finite-length optimized Nyquist prototype filter is designed. The optimized Nyquist pulse can suppress the OOBR of the GFDM system more effectively compared with the traditional Nyquist pulses.

The 'Nigerian Diet' and Its Evolution: Review of the Existing Literature and Household Survey Data.

Natural and social science studies have commonly referenced a 'typical' or 'habitual' Nigerian diet, without defining what such a diet entails. Our study, based on a systematic review of the existing literature and an analysis of household-level survey data, describes the general outline of a common Nigerian diet and how it varies based on spatial, demographic, and socio-economic characteristics. We further try to establish whether Nigeria has embarked on a dietary transition common in most modern economies, marked by a greater consumption of processed foods, fats, and sugar at the expense of traditional whole cereals and pulses. We conclude that while a traditional Nigerian diet is still relatively healthy from an international perspective, it has indeed been transitioning, with an increasing inclusion of high-energy, high-fat, and high-sugar processed foods and a related growing incidence of overweight, obesity, and diet-related non-communicable diseases.

Pulsed selective excitation theory and design in multiphoton MRI

Excitation in MRI is traditionally done at the Larmor frequency, where the energy of each radiofrequency photon corresponds to the energy difference between two spin states. However, if multiple radiofrequencies are employed, then multiphoton excitation can also occur when the sum or difference of multiple photon frequencies equals the Larmor frequency. Although multiphoton excitation has been known since the early days of NMR, it has been relatively unexplored in MRI. In this work, equations and principles for multiphoton selective RF pulse design in imaging are presented and experimentally demonstrated. In particular, the case where there are radiofrequency fields in both the traditional xy-direction and non-traditional z-direction is considered. To produce the z-direction radiofrequency field, an additional uniform coil was added to a clinical MRI scanner. Using this coil, two-photon slice-selective pulses were designed to be equivalent to traditional pulses, producing similar excitation, slice profiles, and in vivo images. Being the result of a combination of multiple radiofrequency fields instead of just one, two-photon pulses have more flexibility in how their parameters can be changed. Although individual multiphoton excitations are less efficient than their traditional counterparts, when the z-direction radiofrequency field is spatially non-uniform, multiple multiphoton resonances can be simultaneously used at different locations to produce simultaneous multislice excitation with the same pulse duration but less tissue heating than a naive implementation. In particular, non-uniform z-direction radiofrequency fields with negligible added tissue heating provided by oscillating the MRI scanner’s gradient fields at kilohertz frequencies were used to excite multiple slices simultaneously with less high-frequency xy-direction radiofrequency power. For an example three-slice excitation, we achieve half the xy-direction radiofrequency power compared to the naïve approach of adding three single-slice pulses. For conventional or unconventional applications, multiphoton excitation may be of interest when designing new MRI systems.

2D BP/InSe Heterostructures as a Nonlinear Optical Material for Ultrafast Photonics.

The BP/InSe heterojunction has attracted the attention of many fields in successful combined high hole mobility of black phosphorus (BP) and high electron mobility of indium selenide (InSe), and enhanced the environmental stability of BP. Nevertheless, photonics research on the BP/InSe heterostructure was insufficient, while both components are considered promising in the field. In this work, a two-dimensional (2D) BP/InSe heterostructure was fabricated using the liquid-phase exfoliation method. Its linear and non-linear optical (NLO) absorption was characterized by ultraviolet−visible−infrared and Open-aperture Z-scan technology. On account of the revealed superior NLO properties, an SA based on 2D BP/InSe was prepared and embedded into an erbium-doped fiber laser, traditional soliton pulses were observed at 1.5 μm with the pulse duration of 881 fs. Furthermore, harmonic mode locking of bound solitons and dark-bright soliton pairs were also obtained in the same laser cavity due to the cross-coupling effect. The stable mode-locked operation can be maintained for several days, which overcome the low air stability of BP. This contribution further proves the excellent optical properties of 2D BP/InSe heterostructure and provides new probability of developing nano-photonics devices for the applications of double pulses laser source and long-distance information transmission.

Broadband composite pulse for quantum sensing with a solid-state spin in diamond

High fidelity quantum operation of qubits plays an important role in realistic quantum sensing. It becomes more challenging when there are inevitable interactions between qubits in the solid system. We employ a composite pulse sequence to deal with the problems. The electron spin state of the nitrogen-vacancy center in diamond is flipped with high fidelity by the composite pulse at room temperature. In contrast with traditional rectangular pulses, the composite pulse has a wider excitation profile at the same Rabi frequency. Hence, the three sublevels of host nitrogen nuclear spin can be flipped efficiently and simultaneously, which enhances the signal contrast and detection sensitivity of quantum sensing universally. The enhancement effect works over a wide range of bias magnetic fields. Our scheme can be used for sensing temperature, strain, and electric field and can be applied to other spin–spin coupling systems.

Melting of Titanium by a Shock Wave Generated by an Intense Femtosecond Laser Pulse

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

Hydrazone organics with third-order nonlinear optical effect for femtosecond pulse generation and control in the L-band

Dissipative solitons are generalized solitons with much larger pulse energy and width than conventional solitons, and the pulse characteristics will be changed dramatically during transmission. Nonlinear photonic absorption device in nonlinear optical resonator can provide saturable absorption effect to generate ultrashort pulses. However, most of the nonlinear photonics devices are based on inorganic materials such as two-dimensional materials with complex production process, and there are relatively few such researches on organics. In this paper, nonlinear photonics absorption device based on hydrazone organics with high molecular polarizability and significant third-order optical nonlinearity generate ultrashort pulses. The dissipative soliton pulses are obtained by controlling the dispersion, and the pulses are compressed to the near-transformation limit of 408 fs with a compression ratio of 44.6. More importantly, the extra-cavity transport properties of dissipative solitons are discussed. Dissipative noise-like soliton pulses are discovered after additional anomalous dispersion fiber, further demonstrating that the physical laws and optical properties of dissipative solitons are completely different from those of traditional optical pulses. We expect that these experimental advances can provide some experimental basis and support for the propagation of dissipative solitons.

Dynamic Pain-Related Changes in Pulse-Graph Measurements in Patients with Primary Dysmenorrhea before and after Electroacupuncture Intervention and Its Correlation with TCM Pattern.

Objective To explore the dynamic changes recorded in pulse graph related to the changes in the severity of pain before and after electroacupuncture (EA) intervention among young women suffering from primary dysmenorrhea (PD). Methods A total of 147 female college students were recruited in this study. Based on participants' symptoms associated with menstruation, they were divided into the PD group and the healthy control group. In addition, participants in the PD group were further sorted into the Cold Coagulation and Blood Stasis Pattern (CCBSP) and Qi Stagnation and Blood Stasis Pattern (QSBSP) based on TCM diagnoses and their pulses differences. Participants in the PD group received EA at maximal pain during menstruation. The primary acupuncture points selected were SP 6 and RN 3, additional RN 4 for CCBSP, and LR 3 for QSBSP. Four observation time points were 7–10 days before menstruation (T0), maximal pain during menstruation (T1), immediately after EA (T2), and 30 mins after EA (T3). The severity of pain was assessed by a visual analog scale (VAS) along with a pulse analyzer to record the variations of the pulse graph throughout the changes of pain level. Results (1) The average VAS score in the PD group decreased from 5.44 ± 1.46 at T1 to 1.72 ± 1.27 at T2 and 1.59 ± 1.30 at T3. The average VAS score in participants of CCBSP at T1, T2, and T3 was higher than that of QSBSP. (2) At T1, h2, h3, h4, and w1/t were all significantly increased, compared with those at T0. At T2, t and t5 were both significantly increased, and w1/t, t1, and t1/t were all significantly decreased, compared with those at T1. At T3, w1/t, t1, and t1/t were all significantly increased, and t and t5 were both significantly decreased, compared with those at T2. (3) Comparing the pulse graphs between the healthy control and the PD groups, h1 was significantly lower at T0; w1/t was significantly higher at T1; t was significantly higher at T2; and t1 and t1/t were both significantly higher at T3 in PD group. (4) When comparing the pulse graphs between QSBSP and CCBSP, t4/t5 was significantly higher at T0 and t1 was significantly higher at T1 in the CCBSP group. Conclusion EA is effective in relieving primary dysmenorrhea. Our results showed the opposite changing of the pulse graph recorded before the onset of pain to the maximum pain and that from maximum pain to pain relief. Indeed, there were differences in the recorded pulse graphs between CCBSP and QSBSP (two patterns of PD) as described in traditional Chinese pulses diagnosis. The study has been registered in the Chinese Clinical Trial Registry (registered number: ChiCTR2000040065; registered date: 2020/11/19).

Single- and bound-state soliton mode-locked Er-doped fiber laser based on graphene/WS2 nanocomposites saturable absorber

We report a passively mode-locked Er-doped fiber laser based on WS2, graphene, and graphene/WS2 (G/WS2) nanocomposites saturable absorber (SA), respectively. These materials were easily prepared by liquid phase epitaxy (LPE) method with isopropanol (IPA). Compared with pure graphene or pure WS2, the film of G/WS2 nanocomposites possesses low nonsaturable loss (31%) and low saturable intensity (12.78 MW/cm2), which is of benefit to achieve passive mode-locked fiber laser. Stable traditional soliton pulses were generated with central wavelength of 1566.7 nm, spectral width of 7.3 nm, pulse duration of 357 fs, and repetition rate of 22.86 MHz. Further, we present the bound-state soliton mode-locked based on G/WS2-SA with a modulation period of 4.9 nm, soliton spacing of 1.67 ps and pulse width of 353 fs. Our work extends the studies for G/WS2 nanocomposites in ultrafast photonics applications.

Surface functionalization of Ta4C3 MXene for broadband ultrafast photonics in the near-infrared region

Recently, MXene has set off a great research boom in the optoelectronic field benefiting from its strong conductivity, eminent broadband absorption, and tailorable electronic/optical properties. In this paper, two-dimensional tantalum carbide (Ta4C3) MXene nanosheets were successfully synthesized based on a two-step liquid exfoliation strategy. Firstly, the role of surface termination with different adsorption structures on the electronic and diverse optical properties of Ta4C3Tx MXene were firstly investigated theoretically via first-principles with density functional theory. Interestingly, the simulation revealed that the oxidized and hydroxylated Ta4C3 MXene featured significantly enhanced optical absorption properties in the near-infrared (NIR) band compared with the pristine bare Ta4C3 nanosheets. Besides, the third-order nonlinear optical (NLO) characteristics of the surfaced terminated Ta4C3 nanosheets were measured by the typical Z-scan techniques at 1 μm. The maximum effective nonlinear absorption coefficient was determined to be -0.78 cm/GW, indicating the great potential as a nonlinear material in NIR band. The nonlinear refractive index, real and imaginary parts of the third-order NLO susceptibility were also obtained. Furthermore, the endowment as an excellent broadband optical modulator was strongly acknowledged utilizing Ta4C3 MXene as saturable absorbers for NIR mode-locking operation at 1044 nm and 1557 nm, respectively. Both highly stable dissipative soliton and traditional soliton pulses were generated. Our results demonstrated the excellent broadband nonlinear absorption in NIR regime of terminal functionalized Ta4C3 MXene and might open a new avenue to the Ta4C3-based advanced ultrafast photonic devices.

Band structure tuning of g-C3N4 via sulfur doping for broadband near-infrared ultrafast photonic applications

Abstract Graphitic carbon nitride (g-C3N4) featuring a stable heptazine ring structure and high polymerization degree, was indexed as a high thermochemical stability material, attracting rising research enthusiasm for diverse applications. However, the poor near-infrared (NIR) optical absorption and resulting limited NIR applications were pronounced for g-C3N4 due to its large bandgap of 2.7 eV. In the present work, sulfur-doping was manifested by first-principles calculations to introduce impurity level and result in anisotropic spin splitting in g-C3N4 for enhancing broadband nonlinear optical characteristics in NIR regime. The modified sulfur-doped g-C3N4 (S-C3N4) exhibited the maximum effective nonlinear absorption coefficient to be −0.82 cm/GW. Pulse duration within hundred nanoseconds was realized with high modulation stability employing S-C3N4 as saturable absorber in Q-switching operations. Moreover, broadband ultrafast photonics properties were successfully demonstrated in constructed ytterbium-doped and erbium-doped fiber lasers, generating highly stable dissipative soliton and traditional soliton mode-locking pulses. The presented S-C3N4 nanomaterial with remarkable nonlinear optical performances might explicitly boost the development and application of g-C3N4 materials in advanced optoelectronic and ultrafast photonic devices.