Average Pulse Research Articles

22-W average power high pulse energy multipass-cell-based post-compression in the green spectral range.

A gas-filled multipass-cell-based post-compression of 515 nm wavelength second-harmonic pulses of an Yb:fiber laser from 240 fs to 15.7 fs is presented. The system delivers 0.44 mJ of pulse energy, 22.4 W of average power at 50.8 kHz with an overall efficiency of more than 40%. These results display the capabilities of multipass-cell-based post-compression schemes to move from the well-established near infrared spectral region to the undeveloped visible regime, allowing for high efficiencies in conjunction with energetic ultrashort pulses at high repetition rates. The unique combination of parameters in the green spectral range offers an immense potential for future developments of high photon flux higher-order harmonic sources.

Coherent Combining of Phase-Steerable High Power Microwaves Generated by Two X-Band Triaxial Klystron Amplifiers with Pulsed Magnetic Fields

We report the first experimental demonstration of coherent combining of phase-steerable high power microwaves (HPMs) generated by X-band relativistic triaxial klystron amplifier modules under the guidance of pulsed magnetic fields. Electronically agile manipulation of the HPM phase is achieved with a mean discrepancy of 4° at the gain level of 110dB, and the coherent combining efficiency has reached as high as 98.4%, leading to combined radiations with equivalent peak power of 4.3GW and average pulse duration of 112ns. The underlying phase-steering mechanism during the nonlinear beam-wave interaction process is furthermore explored by particle-in-cell simulation and theoretical analysis. This Letter paves the way for high power phase array in large scale and may stimulate new interest in research of phase-steerable high power masers.

Generation of soliton mode-locked erbium-doped fibre laser with vanadium aluminum carbide thin film

Picosecond laser pulses are showing increasing importance in various industrial and scientific applications. Here, we exploit the saturable absorption of Vanadium Aluminum Carbide (V2AlC) MAX phase to produce soliton pulses in Erbium-doped fibre laser (EDFL) cavity. The V2AlC composite thin film functions as a mode-locker in this work and it was successfully obtained by embedding the commercial MAX phase V2AlC powder into polyvinyl alcohol (PVA). The prepared V2AlC PVA film has a modulation depth of 27% and it was integrated into an EDFL cavity as a saturable absorber (SA) to generate a highly stable soliton pulse, which operates at 1560 nm wavelength. The soliton mode-locked pulse train was successfully obtained with a fixed repetition rate of 969 kHz and pulse width of 3.96 ps as the pump power is set within a range from 77 to 228 mW. At the maximum pump power of 228 mW, the average output power, pulse energy and peak power are 14.81 mW, 15.28 nJ and 3.4 kW, respectively. Overall, these results show the potential of V2AlC MAX-phase material for use in ultrafast generation. The proposed approach is straightforward and can be also applied to other fibre laser operation wavelengths.

Free-running Yb:KYW dual-comb oscillator in a MOPA architecture.

Single-cavity dual-combs comprise a rapidly emerging technology platform suitable for a wide range of applications like optical ranging, equivalent time sampling, and spectroscopy. However, it remains a challenging task to develop a dual-comb system that exhibits low relative frequency fluctuations to allow for comb line resolved measurements, while simultaneously offering high average power and short pulse durations. Here we combine a passively cooled and compact dual-comb solid-state oscillator with a pair of core-pumped Yb-fiber-based amplifiers in a master-oscillator power-amplifier (MOPA) architecture. The Yb:KYW oscillator operates at 250 MHz and uses polarization multiplexing for dual-comb generation. To the best of our knowledge, this is the first demonstration of a single-cavity dual-comb based on this gain material. As the pulse timing characteristics inherent to the oscillator are preserved in the amplification process, the proposed hybrid approach leverages the benefit of both the ultra-low noise solid-state laser and the advantages inherent to fiber amplifier systems such as straight-forward power scaling. The amplifier is optimized for minimal pulse broadening while still providing significant amplification and spectral broadening. We obtain around 1 W of power per output beam with pulses then compressed down to sub-90 fs using a simple grating compressor, while no pre-chirping or other dispersion management is needed. The full-width half-maximum (FWHM) of the radio-frequency comb teeth is 700 Hz for a measurement duration of 100 ms, which is much less than the typical repetition rate difference, making this passively stable source well-suited for indefinite coherent signal averaging via computational phase tracking.

Closing the window on COVID-19 case-control studies.

Closing the window on COVID-19 case-control studies.

Effect of gold-nanoparticle size on microfiber saturable absorber for mode-locked erbium-doped fiber lasers

The optical performance of passively mode-locked erbium-doped fiber laser incorporating gold-nanoparticles (Au-NPs) of different sizes as saturable absorbers (SAs) was compared. A composite of Au-NPs with polydimethylsiloxane was spin coated on the surface of a microfiber waveguide. The fabricated Au-NP-based SA was deployed in a ring cavity erbium-doped fiber laser and its lasing performance was evaluated by comparing SA characteristics as well as pulse qualities among the different Au-NP sizes. The optimum pulse performance was realized when the SA was fabricated with 20 and 40 nm Au-NP size. For the former, time-bandwidth product of 0.34 was demonstrated which was the closest to its bandwidth-limited pulse. As for the latter, the fabricated SA exhibited 4.0% modulation depth and an average pulse duration of 886.7 fs. The research work has demonstrated the functionality of Au-NPs as a saturable absorption material for ultrashort pulses generation. In addition, the influence of nanomaterial size towards the characteristics of saturable absorbers, ergo the quality of laser pulse, was verified. This finding is also valuable in customizing ultrashort pulse output that can effectively suit system performance need.

Accelerations of public transport vehicles: A method to derive representative generic pulses for passenger safety testing

Investigating the postural balance and stability of standing passengers of public transport in laboratory or numerical tests requires generic test pulses, which replicate the acceleration/deceleration characteristics of common public transport vehicles such as buses or trams. We propose a method to generate such test pulses based on measured acceleration time series. The method consists of an automated splitting algorithm, an expansion in Legendre polynomials and a weighted mean to obtain average pulses which are not dominated by the events of highest magnitude. As a demonstration, the method is applied to acceleration time series obtained on public buses in normal operation, resulting in scalable generic pulse shapes. These can be used as the basis of a standardised framework for physical and virtual testing addressing the standing passenger problem.

Complex Dynamical Sampling Mechanism for the Random Pulse Circulation Model and Its Application

The fast multi-pulse spectrum is a spectrum acquisition method that obtains an average pulse amplitude in a dynamic window, which improves the energy resolution by sharpening peaks in the acquired spectra, but produces the counting loss. Owing to the counting loss problem, a counting rate multiplication method based on uniform sampling, also called the pulse circulation method, is presented in this paper. Based on the theory of mathematical statistics and uniform sampling, this method adopted a dynamic sample pool to update the pulse amplitude sample in real time. Random numbers from the uniform distribution were sampled from the sample pool, and the sampled results were stored in the random pulse circulator so that the pulse amplitude information used for spectrum generation was uniformly expanded. In the experiment section, the obtained spectrum was analyzed to verify the multiplication effect of the pulse circulation method on the counting rate and the compensation effect of the fast multi-pulse spectrum algorithm on the counting rate loss. The results indicated that the characteristic peaks of each element in the X-ray spectrogram obtained by the pulse circulation method could realize counting rate multiplication uniformly, and the multiplication ratio of every element was approximately equal. This is of great significance for obtaining an accurate X-ray fluorescence spectrum.

Pediatric Shock Profile in The Pediatric Intensive Care Unit (PICU) of Dr. Soetomo General Academic Hospital

Introduction: Shock is a life-threatening condition caused by circulatory failure which increases morbidity and mortality rate. According to the western literature, about 2% of children are admitted to hospitals worldwide due to shock. Objective: This study aimed to describe the pediatric shock profile of patients in the Pediatric Intensive Care Unit (PICU) of Dr. Soetomo General Academic Hospital between 1 January to 1 December 2019. Materials and Methods: A total of 60 patients were selected as the participants using a descriptive method. Data collection was carried out by recording the exact time the participants first entered the PICU. Furthermore, data were collected based on gender, age, physical and laboratory examination, diagnosis of shock, patients’ outcomes, as well as PRISM III score. Results: The results of this study that the males and children are 51.7% and 53.3%, respectively. At an infant age, the distribution of the highest average pulse and breathing frequency was 135 and 32.2, respectively. The highest average body temperature at the age of adolescents was 37.19°C. Furthermore, the patients' diagnoses were dominated by distributive shock with the highest PRISM III score ≥8 and deaths recorded of 76.6%, 60%, and 61.7%, respectively. The diagnosis results showed that distributive shock leads to the highest mortality with a PRISM III score of 51.7% and 53.3%. Conclusion: Distributive shock contributes to the patient's diagnoses and mortality rate with the highest score of PRISM III being ≥8. From this conclusion, the PICU needs to be more responsive to detect distributive shock in children.

Thermal effects on removal mechanism of monocrystal SiC during micro-laser assisted nanogrinding process

As a hard-brittle material, research into efficient processing methods of monocrystalline SiC with low damage has attracted a lot of attention. In this paper, removal behavior of monocrystalline SiC using micro-laser assisted method is analyzed using molecular dynamics method. This enables an in-depth theoretical analysis of thermal effects on material removal mechanism for 3C–SiC during nanogrinding process. Taking average laser pulse intensity as a variable, the micro deformation mechanism and machinability under the micro-laser assisted method are analyzed in detail. The results show that laser irradiation can directly affect material removal rate and subsurface damage depth of 3C–SiC. The results of this work significantly improve the understanding of the feasibility of micro-laser assisted method and its optimization for 3C–SiC.

High temporal waveform fidelity stimulated Brillouin scattering phase conjugate mirror using Novec-7500.

A high temporal waveform fidelity stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) with high energy efficiency, based on a novel medium, Novec-7500, is proposed and practically achieved in this study. A theoretical analysis reveals that the temporal-domain waveform distortion is caused by the inherent pulse duration compression effect of the SBS, and this undesirable phenomenon can be significantly suppressed by decreasing the compression coefficient (CC afterwards), which is defined as the gain coefficient divided by the phonon lifetime, which coefficient and is identified as the key parameter for high waveform-fidelity in SBS-PCM. The feasibility of this approach was demonstrated experimentally, in which a reflected pulse with waveform symmetry equals to the pump and an average pulse duration of 0.974 τp (τp is the duration of pump) with an energy efficiency of over 90% was achieved using Novec-7500.

Pulse nonlinear compression generated 71.3 W femtosecond laser

<sec>The power of femtosecond lasers based on Ti: sapphire or Yb-doped gain media has reached a high level by using chirped pulse amplification. The dispersive elements are normally employed in CPA devices, thereby increasing the complexity and cost of the laser system. However, for the Nd-doped laser, its power can be amplified to hundreds of microjoules or even several millijoules directly without CPA technology. So compressing the picosecond pulse to obtain femtosecond laser pulses with hundreds of microjoules pulse energy by post-compression technology becomes meaningful. The pulsed post-compression technology is the combination of nonlinear spectral broadening and dispersion compensation. Currently, the most effective method of nonlinear spectral broadening is achieved through self-phase modulation. The multi-pass cell (MPC) device based on self-phase modulation for broadening spectral bandwidth has been extensively studied, since it was demonstrated. The MPC concept demonstrates significant practical benefits. Essentially, it requires only two curved mirrors and a Kerr medium in between, making it a cost-effective and easily implementable method. Moreover, the MPCs are robust, quite insensitive to beam pointing, and can evendeal with small mode mismatch without transmission losses. These favorable characteristics make MPCs very attractive not only for scientific applications, but also for commercial and facility laser systems where reliability is crucial. The striking progress of the technique in the past six years has made it possible to obtain high average power femtosecond laser.</sec><sec>In this work, we demonstrate the generation of a high average power femtosecond laser pulse by nonlinearly compressing the picosecond pulse in the Herriott multi-pass cell device, and the distribution of eigenmode is analyzed. With this efficient and robust scheme, the spectrum is broadened from 0.20 nm to 2.75 nm, with a broadening ratio of 13.75, and the pulse duration of a picosecond amplifier is compressed from 1.25 ps to 780 fs, with a compression factor of 16. The average power before and after pulse compression are 100 W and 71.3 W respectively, so the overall transmission reaches 71.3%. The present scheme offers a viable route to low-cost and simple-configuration high-power femtosecond lasers driven by Nd-doped picosecond amplifiers.</sec>

Overview of Talkative Power Conversion Technologies

Power Line Communication (PLC) and Simultaneous Wireless Information and Power Transfer (SWIPT) are popular examples of applications, where power and information are transmitted simultaneously. In most cases, different devices have been used to generate the power and communication signals independently. Usually, the information is superimposed onto the power signal using an external modulator. Recently, power converters have been used to generate pulses not just for power conversion but also for information transfer simultaneously. This approach represents a fundamental difference because it exploits the signal processing potential of Pulse Width Modulation (PWM), where for power conversion only the average pulse width is used, while the information is represented by the harmonics instead of being filtered out, as typically done in power electronics. The concept of embedding information into the switching ripple generated by a switched-mode power converter has recently been dubbed Talkative Power (TP), in this paper referred as Talkative Power Conversion (TPC). TPC technologies are reviewed in non-isolated and isolated converters in this paper. Potential applications include visible light communications, battery management systems, switching reluctance generators/motors, microgrids, and wireless electric vehicle charging stations. Finally, trending topics are identified.

An Observational Study of Single Pulse of PSR J0835-4510

Vela pulsar (PSR J0835-4510) was observed in L-band with the 40-meter radio telescope at the Haoping Observatory of National Time Service Center, Chinese Academy of Sciences. 38040 single pulses were detected in 56 minutes. The half-maximum line width (W50) of these single pulses ranges from 0.52 to 3.3 ms, with an average value of 1.5 ms. This is smaller than that of the integral profile, which is 1.9 ms. The signal-noise ratio (S/N) of single pulses ranges from 6.8 to 495, with an average S/N value of 32.4. About 58% of the peak of single pulses arrived earlier than the peak of integral pulse profile, the earliest was 2.3 ms earlier. Lognormal distribution fits the radiation energy of single pulses with average μ=−0.02 and standard deviation σ = 0.28. One normal single pulse was detected in the leading edge of the pulsar radiation window, with the S/N values of 47.4. There are 69 single pulses with S/N larger than 5 times the detected average S/N value of single pulses. These strong pulses are relatively narrow, and their W50 ranges from 0.52 to 1.04 ms. These pulses are located near the rising edge of the average pulse profile. There are 23 single pulses detected with bimodal structure. The primary and secondary peaks are located in different radiation regions. It is found that the influences of strong single pulses and double peak single pulses on average pulse profile are different by studying the integral pulse profile of different types of single pulses.

Finite-time contraction stability of a stochastic reaction-diffusion dengue model with impulse and Markov switching.

From the perspective of prevention and treatment of dengue, it is important to minimize the number of infections within a limited time frame. That is, the study of finite time contraction stability (FTCS) of dengue system is a meaningful topic. This article proposes a dengue epidemic model with reaction-diffusion, impulse and Markov switching. By constructing an equivalent system, the well-posedness of the positive solution is proved. The main result is that sufficient conditions to guarantee the finite time contraction stability of the dengue model are acquired based on the average pulse interval method and the bounded pulse interval method. Furthermore, the numerical findings indicate the influences of impulse, control strategies and noise intensity on the FTCS.

Functional state of the peripheral nervous system in miners suffering from chronic lumbosacral radiculopathy of occupational origin

Exercise is a major factor in the development of occupational pathology of the connective tissue and musculoskeletal system, including chronic lumbosacral radiculopathy (LSRP), which accounts for 20% of occupational diseases in Ukraine. Some problems remain insufficiently studied despite a significant number of scientific works devoted to the study of issues of etiology, pathogenesis, features of clinical manifestations, the use of diagnostic and prophylactic measures in LSRP. The criteria for diagnosing changes in the peripheral nervous system need to be clarified and systematized by in-depth study of the functional state of the nervous apparatus in patients with LSRP of professional genesis. The research was carried out in a group of 60 miners of the main professions (coal-cutter, mining worker of a clearing pit (MWCP), drifter) suffering from LSRP. The activity of the neuromuscular apparatus was assessed according to the indices of electroneuromyography (ENMG), namely: the amplitude of the M-response during stimulation at the distal point of the right and left m. Abductor Hallucis, n. Plantar Medial, S1, S2 (mV), as well as indicators of terminal and residual latencies (ms), the speed of the impulse along the indicated nerves (m/s). It was found that the average amplitude of the M-response during stimulation at the distal point m. Abductor Hallucis, n. Plantar Medial in the MWCF group was at 6.37 mV (with a reference value of 4-5.8 mV), the average pulse conduction velocity was 38.46 m/s (with a reference value of 40.00 -50.00 m/s), it was found that most often in the group of coal-cutters (64.2%), a pathological indicator of terminal latency was recorded, while in a group of drifter, it did not go beyond the normal range in one of the surveyed miners suffering from LSRP of occupational genesis. Thus, ENMG of the long nerves of the lower extremities is a useful tool of objectifying the diagnosis of LSRP of ocupational genesis, it allows to determine the degree of impairment of the functional activity of peripheral nerves, neuromuscular synapses and the contractility of the striated muscles.

THE PHYSIOLOGIC COMPLEXITY OF BEAT-TO-BEAT BLOOD PRESSURE FLUCTUATION IS ASSOCIATED WITH FRAILTY IN OLDER ADULTS

Abstract Background Beat-to-beat blood pressure (BP) is an important cardiovascular output and regulated by neurophysiologic elements over multiple temporal scales. The multiscale dynamics of beat-to-beat BP fluctuation has thus been characterized using “BP complexity” and has been linked to age-related adverse health outcomes. We here aimed to examine the relationship of BP complexity to frailty, and if BP complexity mediates the association between arterial stiffness and frailty. Method: A total of 350 older adults completed assessments for frailty (i.e., Fried frailty phenotype criteria), arterial stiffness (i.e., average brachial-ankle pulse wave velocity), and beat-to-beat finger BP. The complexity of beat-to-beat systolic (SBP) and diastolic (DBP) BP series were measured using multiscale entropy. The relationships between frailty, BP complexity and arterial stiffness were examined using ANOVA and linear regression models. The effects of BP complexity on the association between arterial stiffness and frailty were examined using mediation analyses. Results Compared to non-frail, pre-frail and frail groups had significantly elevated lower SBP and DBP complexity (F>11, p< 0.001), and greater arterial stiffness (F=16, p< 0.001). Greater arterial stiffness was associated with lower BP complexity (β<-0.42, p< 0.001). SBP and DBP complexity mediated the association between arterial stiffness and frailty (indirect effects>0.28), account for at least 47% of its total effects on frailty (Mediated proportion: SBP: 50%, DBP: 47%). Conclusion This study demonstrates that BP complexity is associated with frailty in older adults, and mediates the association between arterial stiffness and frailty, suggesting that this metric would serve as a marker to characterize important functions in older adults.

Individual pulse emission from the diffuse drifter PSR J1401 − 6357 using the ultrawideband receiver on the Parkes radio telescope

ABSTRACT In this study, we report on a detailed single pulse analysis of the radio emission from the pulsar J1401 − 6357 (B1358 − 63) based on data observed with the ultrawideband low-frequency receiver on the Parkes radio telescope. In addition to a weak leading component, the integrated pulse profile features a single-humped structure with a slight asymmetry. The frequency evolution of the pulse profile is studied. Well-defined nulls, with an estimated nulling fraction greater than 2 per cent, are present across the whole frequency band. No emission is detected with significance above 3σ in the average pulse profile integrated over all null pulses. Using fluctuation spectral analysis, we reveal the existence of temporal-dependent subpulse drifting in this pulsar for the first time. A clear double-peaked feature is present at exactly the alias border across the whole frequency band, which suggests that the apparent drift sense changes during the observation. Our observations provide further confirmation that the phenomena of pulse nulling and subpulse drifting are independent of observing frequency, which suggest that they invoke changes on the global magnetospheric scale.

Performance comparison of supercontinuum generation using various tapered fiber waist diameters with a mode-locked fiber laser

Different waist diameters of tapered fibers were proposed and demonstrated as a nonlinear medium to compare the performance in generating supercontinuum (SC) output with a mode-locked fiber laser (MLFL) as the laser source. The MLFL source was developed using the nonlinear polarization (NPR) technique. The average output power, peak power, and pulse energy of MLFL were 3.98 mW, 0.115 kW, and 0.2 nJ, respectively. The MLFL also has a repetition rate of 19.55 MHz with a signal-to-noise ratio (SNR) of 62.92 dB. Moreover, the MLFL was amplified and launched into the tapered fiber to compare the performance of SC generation at different waist diameters. The spectral broadening generated from tapered fiber with 10 µm, 20 µm, and 30 µm waist diameters were 690 nm, 612 nm, and 550 nm, respectively. The peak power of SC output of 10 µm, 20 µm, and 30 µm tapered fibers was calculated to be 31.04 kW, 28.14 kW, and 25.72 kW, respectively. The experimental results show that the tapered fiber was an effective nonlinear device for supercontinuum generation, which will benefit various optical applications.

Prediction of Health Problems Using Deep Learning Images and Bio-Signals

We propose a study to predict health abnormalities by analyzing body temperature and the heart rate variability parameters of pulse waves. The research method firstly selects fever by applying a deep learning model to thermal images, and secondly, extracts heart rate variability from pulse waves through a photo-plethysmograph sensor. It analyzes the relevance of body temperature and health status by dividing the presence or absence of fever cases and comparing parameters related to autonomic nerves and stress cases. As a result of the experiment, the control group with normal body temperature had a mean pulse variability of 37.65, SDNN of 64.83, and RMSSD of 42.24. In contrast, in the experimental group, which consisted of individuals with fever, the average pulse variability was 31.91, the SDNN was 42.34, and the RMSSD was 26.80. Our research expects to be applicable to a thermal imaging system that can measure body temperature and bio-signals together and show the predicted results of health status for fever cases.