Output Pulse Research Articles

Self-seeded quasi-continuous-wave Er:ZBLAN fiber laser

A self-seeding phenomenon is forecasted in a pulse-pumped Er:ZBLAN fiber laser. A non-zero lasing power, serving as a seeding power for subsequent output pulse, between two adjacent output pulses, will appear in a pulse-pumped Er:ZBLAN fiber laser when the average pump power is increased to a certain value. The seeding power plays an essential role for the transformation of gain-switching operation to quasi-continuous-wave (QCW) operation in a pulse-pumped Er:ZBLAN fiber laser, and is responsible for the suppression of chaotic spikes in the output QCW pulse as well. Under certain conditions, moreover, stable QCW output pulses are expected to be generated in pulse-pumped the Er:ZBLAN fiber laser with the assistance of the self-seeding power. The pulse-pumped Er:ZBLAN fiber laser, referred to as a self-seeded Er:ZBLAN fiber laser, has great potential for stable QCW pulse generating with nearly the same duration and temporal profile as those of pump pulse.

Finite element analysis of pulse sharpening effect of gyromagnetic nonlinear transmission line based on Landau–Lifshitz–Gilbert equation

Ferrite-loaded gyromagnetic nonlinear transmission line (GNLTL) provides a possible option to compress an input pulse to a narrower width for its remarkable sharpening effect. However, it is difficult to accurately predict the output of the GNLTL due to the complex interaction between the magnetic moment of ferrite and the bias magnetic field. In this paper, a finite element model of the GNLTL is established based on the Landau–Lifshitz–Gilbert equation to investigate the performance of the GNLTL. To validate this model, a prototype is used for experimental comparison. The result demonstrates good agreement between experiment and simulation. This paper further explores the influence of the bias magnetic field and the length of the GNLTL on the output pulse. Moreover, a method to sharpen the falling edge is proposed based on the reflection and superposition of the GNLTL output. Simulation and experimental results show its effectiveness and feasibility.

Optimal Prescription for Superior Outcomes: A Comparative Analysis of Inter-Individual Variability in Adaptations to Small-Sided Games and Short Sprint Interval Training in Young Basketball Players.

This study compared the inter-individual variability in adaptive responses to six weeks of small-sided games (SSG) and short sprint interval training (sSIT) in young basketball players. Thirty well-trained young athletes (age: 16.4 ± 0.6 years; stature: 190 ± 8.4 cm; weight: 84.1 ± 8.2 kg) voluntarily participated and were randomly assigned to SSG (3 sets of 5 min 3v3 on full length (28 m) and half-width (7.5 m) court, with 2 minutes of passive recovery in-between), sSIT (3 sets of 12 × 5 s sprinting with 20 s recovery between efforts and 2 min of rest between sets), or CON (routine basketball-specific technical and tactical drills) groups, each of ten. Before and after the training period, participants underwent a series of laboratory- and field-based measurements to evaluate their maximum oxygen uptake (V̇O2max), first and second ventilatory threshold (VT1 and VT2), oxygen pulse, peak and average power output (PPO and APO), linear speed, change of direction (COD), countermovement jump (CMJ), and vertical jump (VJ). Both SSG and sSIT sufficiently stimulated adaptive mechanisms involved in enhancement of the mentioned variables (p < 0.05). However, sSIT resulted in lower residuals in percent changes in V̇O2max (p = 0.02), O2pulse (p = 0.005), VT1 (p = 0.001), PPO (p = 0.03), and linear speed (p = 0.01) across athletes compared to the SSG. Moreover, sSIT resulted in more responders than SSG in V̇O2max (p = 0.02, φ = 0.500), O2pulse (p = 0.003, φ = 0.655), VT1 (p = 0.003, φ = 0.655), VT2 (p = 0.05, φ = 0.436), and linear speed (p = 0.05, φ = 0.420). Our results indicate that sSIT creates a more consistent level of mechanical and physiological stimulus than SSG, potentially leading to more similar adaptations across team members.

Intelligent Light Emitting Diode Flashing Supplementary Lighting Control Design and Its Big Data Illumination Analysis

Considering the inherent advantages of the Light Emitting Diode (LED) in the field of illumination, this work designs an intelligent supplementary lighting system using LED as the light source. Combining microcontroller and electronic circuit theory, the circuit is built with the microcontroller PIC16F873 as the core control chip. The system utilizes an external 220 V AC-20 V DC conversion power supply, hence operating on a 20 V DC power source. The system consists of four hardware parts: the onboard power supply uses TI-produced TPS54331 as the control chip to achieve voltage conversion; the external signals (flashing and burst flashing signals) are isolated from the microcontroller through an optocoupler circuit; the PWM pulses output from the microcontroller’s RC1/CCP2 pins drive the corresponding switching tubes to achieve the flashing function; the flashing synchronization signal is output externally after optocoupler isolation, and its synchronous output with the flashing signal is achieved through an optocoupler after LED conduction; the circuit is established using TI-produced differential bus transceiver SN65LBC184D to convert the external 485 differential signal to the level signal required by the microcontroller. In the experiment, after completing the hardware design, connecting the LED panel, and debugging the test program, it is found that the designed lighting system has a good supplementary lighting effect. According to the PWM output waveform, the flashing effect meets the design expectations. The Hadoop big data computing platform is introduced. Simulation testing reveals that under no backlight conditions, the system achieves an illumination intensity of around 20 klx at a distance of about 10 meters. With backlight conditions, the system maintains an illumination intensity of around 1.5 klx at a distance of about 10 meters. Further calculations are performed to analyze the variation in foot traffic within the test area’s illumination over 24 hours. The total illumination intensity during different time intervals is compiled, confirming that the system can autonomously adjust the illumination intensity of the area based on changes in foot traffic.

Resonant Ring with a Gain of 36 for Use with a 1 MW 110 GHz Gyrotron

A 110 GHz quasi-optical ring resonator, designed for use with a 1 MW pulsed gyrotron, has been built and successfully tested using a 100 mW solid-state source. A low reflectance (2.4%) input coupler and a low-loss, four-mirror ring demonstrated a compression ratio, defined as the ratio of output to input power, of 36. The 6 ns output pulses were generated from the 2 m length ring using a silicon laser-driven semiconductor switch (LDSS). The quasi-optical ring resonator was designed with large waist sizes so that input pulses of up to 1 MW will stay under the 35 kV/cm electric field limit for ionization in ambient air. Maximum compression gain was achieved by matching the input coupling fraction to the round trip loss in the ring, achieving close to critical coupling. The experimental output pulse shape obtained after firing the LDSS was modeled using the reflectance, transmittance, and absorptance of the switch vs. time and vs. laser pulse fluence, with good agreement found with theory. The timing for the peak energy efficiency of 32% was found and the main loss mechanism limiting that efficiency was found to be the absorptance in the silicon wafer.

V2O5/Ti3C2 MXene-Based Solid-State Passively Mode-Locked Tm:YAP laser at 2 μm

In the present work, V2O5/Ti3C2 MXene hybrid nanomaterials were successfully synthesized. The morphology and structure of the prepared V2O5/Ti3C2 MXene were investigated, and the results showed excellent bonding and strong interaction between Ti3C2 MXene and V2O5 nanoparticles. The nonlinear absorption properties of V2O5/Ti3C2 MXene nanocomposites at 2 μm have been investigated using power transfer techniques, and the large modulation depth of the material gives it potential for applications in nonlinear optics. As a result, a 2 μm solid-state mode-locked pulsed laser with V2O5/Ti3C2 MXene as a saturable absorber has been realized for the first time, generating a pulsed laser output as short as 657 ps, which corresponds to an average output power of 0.67 W. The results show that the synthesized V2O5/Ti3C2 MXene hybrid nanomaterials, which have a large optical nonlinearity, can be applied to generating an ultrashort 2 μm pulsed laser.

Neuron Circuit Based on a Split-gate Transistor with Nonvolatile Memory for Homeostatic Functions of Biological Neurons.

To mimic the homeostatic functionality of biological neurons, a split-gate field-effect transistor (S-G FET) with a charge trap layer is proposed within a neuron circuit. By adjusting the number of charges trapped in the Si3N4 layer, the threshold voltage (Vth) of the S-G FET changes. To prevent degradation of the gate dielectric due to program/erase pulses, the gates for read operation and Vth control were separated through the fin structure. A circuit that modulates the width and amplitude of the pulse was constructed to generate a Program/Erase pulse for the S-G FET as the output pulse of the neuron circuit. By adjusting the Vth of the neuron circuit, the firing rate can be lowered by increasing the Vth of the neuron circuit with a high firing rate. To verify the performance of the neural network based on S-G FET, a simulation of online unsupervised learning and classification in a 2-layer SNN is performed. The results show that the recognition rate was improved by 8% by increasing the threshold of the neuron circuit fired.

Ag/MXene as Saturable Absorber for Tm:Ho Co-Doped Q-Switched Fiber Laser.

Q-switched fiber lasers have become reliable light sources for generating high-energy pulses, which can be passively modulated by saturable absorbers with excellent nonlinear optical properties. The composite combining Ag and MXene exhibits a broadband nonlinear response and high modulation depth, making it a promising candidate for saturable absorbers in pulsed lasers. Herein, we demonstrate a Q-switched Tm:Ho co-doped fiber laser centered at 2 µm, where the Ag/MXene composite serves as a saturable absorber to generate pulses. The typical spectrum, pulse train, and radio frequency spectrum of Q-switched pulses were observed, in which the 60 dB signal-to-noise ratio was higher than that of 2 µm Q-switched fiber lasers based on other materials, demonstrating the stability of the output pulses. Additionally, the long-term stability of the laser was evaluated over 2 h, where the well-maintained central wavelength and output power also indicated the robustness of the Q-switched laser. Furthermore, the influence of the pump power on the parameters of Q-switched pulses was also investigated, which is conducive to control the output characteristics of lasers. Specifically, the pulse width of the Q-switched pulse decreased, while the repetition rate, output power, and single pulse energy all increased with the increase in pump power. These experimental results demonstrate the ability of Ag/MXene as a saturable absorber and show its potential for generating high-performance pulses in ultrafast lasers.

A CMOS Current-Mode Vertical-Cavity-Semiconductor-Emitting-Laser Diode Driver for Short-Range LiDAR Sensors.

This paper presents a current-mode VCSEL driver (CMVD) implemented using 180 nm CMOS technology for application in short-range LiDAR sensors, in which current-steering logic is suggested to deliver modulation currents from 0.1 to 10 mApp and a bias current of 0.1 mA simultaneously to the VCSEL diode. For the simulations, the VCSEL diode is modeled with a 1.6 V forward-bias voltage and a 50 Ω series resistor. The post-layout simulations of the proposed CMVD clearly demonstrate large output pulses and eye-diagrams. Measurements of the CMVD demonstrate large output pulses, confirming the simulation results. The chip consumes a maximum of 11 mW from a 3.3 V supply, and the core occupies an area of 0.1 mm2.

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

THz-TDS with gigahertz Yb-based dual-comb lasers: noise analysis and mitigation strategies

We investigate terahertz time-domain spectroscopy using a low-noise dual-frequency-comb laser based on a single spatially multiplexed laser cavity. The laser cavity includes a reflective biprism, which enables generation of a pair of modelocked output pulse trains with slightly different repetition rates and highly correlated noise characteristics. These two pulse trains are used to generate the THz waves and detect them by equivalent time sampling. The laser is based on Yb:CALGO, operates at a nominal repetition rate of 1.18 GHz, and produces 110 mW per comb with 77 fs pulses around 1057 nm. We perform THz measurements with Fe-doped photoconductive antennas, operating these devices with gigahertz 1 µm lasers for the first time, to our knowledge, and obtain THz signal currents approximately as strong as those from reference measurements at 1.55 µm and 80 MHz. We investigate the influence of the laser’s timing noise properties on THz measurements, showing that the laser’s timing jitter is quantitatively explained by power-dependent shifts in center wavelength. We demonstrate reduction in noise by simple stabilization of the pump power and show up to 20 dB suppression in noise by the combination of shared pumping and shared cavity architecture. The laser’s ultra-low-noise properties enable averaging of the THz waveform for repetition rate differences from 1 kHz to 22 kHz, resulting in a dynamic range of 55 dB when operating at 1 kHz and averaging for 2 s. We show that the obtained dynamic range is competitive and can be well explained by accounting for the measured optical delay range, integration time, as well as the measurement bandwidth dependence of the noise from transimpedance amplification. These results will help enable a new approach to high-resolution THz-TDS enabled by low-noise gigahertz dual-comb lasers.

Updates on Impact Ionisation Triggering of Thyristors

High voltage (HV) generators are used in multiple industrial and scientific facilities. Recent publications have demonstrated that triggering industrial thyristors (relatively slow switching devices) in overvoltage mode, also called impact ionization mode, significantly enhances their dU/dt and dI/dt characteristics. This novel triggering methodology necessitates the application of substantial overvoltage between the thyristor’s anode and cathode, delivered with a swift slew rate exceeding 1 kV/ns. The adoption of compact pulse generators constructed from commercially available off-the-shelf components (COTS) opens up avenues for deploying this technology across various domains, including the implementation of high-speed kicker generators in particle accelerators. In our methodology, we employed commercially available high-voltage SiC MOSFETs along with a custom-designed fast gate driver. This driver was conceptualized based on the recent development of gate boosting techniques, featuring a driving voltage exceeding 600 V. The gate driver for these MOSFETs comprises three key components: a level-shifter with NMOS and PMOS transistors, a compact Marx generator with two avalanche transistors, and a GaN HEMT in a high input and low output impedance configuration. The proposed gate-boosting driver achieves a slew rate exceeding 1 kV/ns for the driving pulse. Furthermore, we demonstrate that with this driver, a 1.7 kV rated SiC MOSFET can produce an output pulse of 1.45 kV and a maximum slew rate of ≈2.5 kV/ns. This gate-boosting driver aims to minimize commutation times, achieves a slew rate of over 1 kV/ns, and handle higher loads, making it ideal for impact ionization triggering of industrial thyristors.

A low-power metal–oxide scan driver circuit outputting non-overlapping pulses with DC power-supplied buffer

This paper proposes a novel metal–oxide (MOx) thin-film transistors (TFT)-based scan driver circuit with a DC power-supplied buffer. This circuit has two parts: a ‘carry generation block (CGB)’ and an ‘output generation block (OGB).’ The CGB generates a carry pulse by the bootstrapping effect of pull-up TFT with the aid of clock signal; clock-supplied bootstrapping. Then the OGB is controlled by the carry pulse, and the output pulse is generated by the bootstrapping effect of pull-up buffer TFT with DC power supply; DC-supplied bootstrapping. In the proposed circuit, the pull-up TFT in CGB does not need to have wide dimensions because the carry signal is separated from the large capacitive load in the pixel area. Accordingly, the capacitive load of the clock signal is significantly reduced, and the dynamic power consumption associated with clock toggling decreases remarkably compared with the conventional scan driver circuit that uses the clock-supplied bootstrapping for the wide output buffer TFT. In addition, a bootstrapping inverter in OGB makes the output pulse width the same as the clock-high duration, preventing the output pulses from overlapping, which is required for most of the organic light-emitting diode (OLED) pixel circuits with in-pixel compensation.

A High-Energy, Wide-Spectrum, Spatiotemporal Mode-Locked Fiber Laser.

In this article, we demonstrate a high-energy, wide-spectrum, spatiotemporal mode-locked (STML) fiber laser. Unlike traditional single-mode fiber lasers, STML fiber lasers theoretically enable mode-locking with various combinations of transverse modes. The laser can deliver two different STML pulse sequences with different pulse widths, spectra and beam profiles, due to the different compositions of transverse modes in the output pulses. Moreover, we achieve a wide-spectrum pulsed output with a single-pulse energy of up to 116 nJ, by weakening the spectral filtering and utilizing self-cleaning. Strong spatial and spectral filtering are usually thought to be necessary for achieving STML. Our experiment verifies the necessity of spatial filtering for achieving STML, and we show that weakening unnecessary spectral filtering provides an effective way to increase the pulse energy and spectrum width of mode-locked fiber lasers.

Gain-Switched Er-Doped Fluoride Fiber Laser at ~3.75 μm

We demonstrate a pulsed Er-doped ZBLAN fiber laser operating at 3.75 μm based on the gain-switching scheme. A diffraction grating is introduced as a wavelength selection component to enable stable lasing in this long-wavelength region that deviates from the emission peak of 4F9/2→4I9/2 transition in Er3+. Different from the conventional gain-switching behavior where the pulse repetition frequency of the output laser is same as the that of the pump, the gain-switched laser demonstrated here shows a variable pulse repetition frequency, which accounts for 1/n (n = 4, 3, 2) of the pump pulse repetition frequency, in response to the 1950 nm pump power. The output pulse characteristics, including average output power, repetition frequency, pulse duration, and peak power, are investigated in detail. Over 200 mW average output power at 3.75 μm was obtained at 12 W of 1950 nm pump power. This work demonstrates that the Er-doped ZBLAN fiber laser, in combination with gain-switched scheme, is a feasible and promising approach to generate powerful pulsed emission &gt; 3.7 μm.

Synchronous mode-locking of solid-state lasers by difference frequency generation.

This Letter introduces a novel, to the best of our knowledge, method for achieving mode-locking and synchronization of mode-locked output pulses from two lasers. The proposed technique leverages parametric gain from difference frequency generation. Specifically, a Nd:YAG laser is mode-locked by single-pass mode-locked pulses from a mode-locked Ti:sapphire laser using an intracavity nonlinear crystal. When the continuous-wave laser is not actively pumped, the system functions as a synchronously pumped optical parametric oscillator. This novel approach has the potential to enable new devices, especially for pump-probe applications or for generation of mode-locked pulses in spectral regions where conventional mode-locked devices are typically not available.

5.4 W, 2.35 µm cascaded Raman fiber laser pumped by dissipative soliton resonance-like pulses

We present a nonlinear amplifying loop mirror-based mode-locked fiber laser. By adjusting the pump power, the proposed laser exhibits a dissipative soliton resonance (DSR)-like pulse operation with a maximum pulse width of 150 ns. Subsequently, a three-stage Tm3+-doped fiber amplifier is implemented using a single-mode double-cladding Tm3+-doped fiber to increase the DSR-like pulse output power to 52.5 W, achieving a pump slope efficiency of 47.1% in the main amplifier. A 25 m first-order Raman-gain fiber (UHNA7) is pumped by a DSR-like pulse, and 16.3 W of pure 2.135 µm first-order Raman light with a spectral purity of 73.4% is obtained. Finally, 5.4 W of 2.35 µm second-order Raman light with a spectral purity of 66% is obtained using a 10 m 98% germania-core fiber as a second-order Raman-gain fiber cascaded after UHNA7 fiber. To the best of our knowledge, this is the highest output power ever obtained from a 2.3 µm laser.

A solid-state pulse power sub-nanosecond SiC DSRD-based generator with high-voltage and high repetition frequency for pulse discharge water treatment

Water treatment is one of the most important issues for all walks of life around the world. The unique advantages of the solid-state power electronic pulses in water treatment make it attractive and promising in practical applications. The output voltage, rising time, repetition rate, and peak power of output pulses have a significant impact on the effectiveness of water treatment. Especially in pulse electric field treatment and pulse discharge treatment, the pulse with fast rising time achieves the advantage of generating plasma without corona, which can avoid water heating effect and greatly improve the efficiency of the pulse generator. High repetition rate can significantly reduce the peak power requirement of the pulse in water treatment application, making the equipment smaller and improving the power density. Therefore, the study developed a high-voltage high frequency sub-nanosecond pulse power generator (PPG) system for wastewater treatment. It adopts SiC DSRD (Drift Step Recovery Diode) solid-state switches and realize modular design, which can achieve high performance and can be flexible expanded according to the requirements of water treatment capacity. Finally, an expandable high-voltage PPG for water treatment is built. The output parameters of the PPG include output pulse voltage range from 1 to 5.28 kV, rise time <600 ps (20%–90%), repetition up to 1 MHz. The experiment results of PPG application for pulse discharge water treatment is presented. The results indicate that the proposed generator achieves high-efficiency degradation of 4-Chlorophenol (4-CP), which is one of the most common chlorophenol compounds in wastewater. From experiment, the homemade system can degrade 450 mL waste water containing 500 mg/L 4-CP in 35 min, with a degradation rate of 98%. Thereby, the requirement for electric field intensity decreased. Through the further quantitative analysis, the impact of frequency, voltage, and electrode spacing on the degradation effect of 4-CP is confirmed.

Study on a rotational symmetry structure pulse forming network with low-impedance for compact pulse drivers.

A pulse forming network (PFN) is a significant component, contributing a lot to the overall dimension of pulse generators. In order to both reduce the size of PFN and improve the output waveform quality, this paper proposes a compact low-impedance PFN with a rotational symmetry structure. The PFN consists of four groups of Blumlein pulse forming units (PFUs) connected in parallel along the angular direction, and the spline curve structure is applied in each PFU, which achieves a higher space utilization rate. The theoretical maximum energy density of PFN is 6.6 J/L as the dimensions of PFN are φ500 × 138mm. Field-circuit co-simulation is carried out based on the spatial model of PFN and the double switch modulation circuit to analyze the effects of switch delay time (time between main switch and steep discharge switch), as well as the output port position affecting the output pulse waveform. The results show that the PFN is appropriate to achieve quasi-square wave pulse modulation as the switch delay time is 290ns with the output port positioned at the periphery. The verification experiments are also carried out. The results show that the PFN can generate a quasi-square wave pulse with an output voltage of 49.6kV, a pulse width of 83ns, and a peak power of 1 GW on a matched load. The output pulse exhibits a distinct flat top, with the fluctuation of the plateau being less than 3%.

A pulse selection algorithm for SiPM-coupled CLYC detectors

SiPM-coupled Cs2LiYCl6:Ce3+ (CLYC) detectors are widely used for detecting neutrons and gamma rays in mixed radiation environments. Intensities and energies are obtained from the output pulses of the detector, including normal and anomalous pulses. Since anomalous pulses can negatively affect measurement accuracy, this study designs a pulse selection algorithm to improve them. This algorithm calculates the ratio of the mean to the standard deviation of an output pulse in a particular time window and categorizes it as normal or anomalous. The algorithm also uses the difference in ratio value between neutrons and gamma rays for pulse shape discrimination. In an experiment using a SiPM-coupled CLYC detector, 200,000 sets of pulses were obtained for 137Cs and Am-Be sources. The results indicate that this method can reject more than 94.2% of anomalous pulses, improving the energy resolution of 137Cs source from 8.9% @ 662 keV to 8.4% @ 662 keV. The figure-of-merit (FOM) of pulse shape discrimination is 1.23 for the Am-Be source, and this method can select specific pulse types based on the pulse-ratio value. In addition, the method is suitable for all pulse-mode detectors.