Pulsed Output Power Research Articles

Utilization of Te as a saturable absorber for mode-locked 2.8 µm Er3+: ZBLAN fiber laser

In this manuscript, we present the experimental realization of a mode-locked Er3+: ZBLAN (ZrF2- BaF2- LaF3- AlF3- NaF) fiber laser operating at mid-infrared (mid-IR) 2.8 μm band, achieved through the utilization of Tellurium (Te) as the saturable absorber (SA). An exploration of their nonlinear optical absorption properties at 2.8 μm was undertaken employing a dual-channel detection methodology. Our investigation reveals that the Te-SA prepared exhibits a significant broadband saturable absorption response, thereby confirming its suitability as SA for passive mode-locked fiber laser at 2.8 μm. The peak average output power pulse and energy of the mode-locked Er3+: ZBLAN fiber laser are 41.2mW and 1.632nJ, respectively. These measurements were conducted at a repetition rate of 25.25 MHz, accompanied by a signal-to-noise ratio (SNR) of 60 dB at a transmit pump power of 600 mW. This is the first demonstration of a mode-locked fiber laser operating in the 2.8 µm mid infrared band using Te-SA.

Experimental study on the discharge characteristics of high-voltage nanosecond pulsed discharges and its effect on the ignition and combustion processes

Non-equilibrium plasma has been proven to expand ignition limits and enhance combustion. This paper uses high-voltage nanosecond pulsed discharge (NPD) to generate non-equilibrium plasma and experimentally studies the discharge characteristics at different parameters in a constant-volume combustion bomb. NPD is used to ignite the methane-air mixture, and the effects of pulse power output voltage and pulse interval (PI) on ignition and combustion processes are studied. In addition, the minimum ignition energy (MIE) at different ignition methods (Transistor coil ignition (TCI) and NPD) is also studied. The results show that the first pulse of NPD discharge has a higher breakdown voltage and discharge energy when using multi-pulse discharge. After the second pulse, the highest breakdown voltage and current tend to stabilize, and the discharge energy remains unchanged. As the PI increases, the breakdown peak voltage and the peak current increase slightly. The study on the MIE of NPD shows that at different mixture concentrations, the MIE of NPD is smaller than that of TCI, and NPD can expand the lean burn limit. An increase in initial temperature can significantly reduce MIE. In addition, when the discharge energy is near the MIE, the combustion stability begins to decrease, and the combustion cycle fluctuates wildly. When the ignition energy is increased, the stability improves, and the combustion fluctuation rate can be maintained within 5%.

Design of a highly efficient reconfigurable C/X dual‐band 15W GaN MMIC power amplifier using amplifier‐switch fusion technique

AbstractThis letter introduces the design of a highly efficient reconfigurable C/X dual‐band power amplifier (PA). Conventional dual‐band designs connect two amplifier branches for each band by a switch, whose transmitting losses will limit the efficiency of the PA. In alternative to the switching solution, the authors propose a novel design method using two branches of output matching networks (OMN) which the 5–6 and 8–12 GHz branch acting as active loads for each other, respectively. The band‐pass OMNs are applied, and parts of the passive matching components are replaced by transistors for channel selection. The proposed design has been simulated, implemented, and measured. The experimental results demonstrate a power added efficiency (PAE) of 45% at a pulsed output power (Pout) of 42 dBm in 5–6 GHz while a PAE greater than 39% at 42 dBm Pout in 8–12 GHz. Moreover, the second and third harmonics of both operating bands are compressed to −35 and −40 dBc, respectively. The proposed design technique addresses the challenges of low‐efficiency and lower‐band harmonic suppression in traditional dual‐band designs, making it suitable for application in next‐generation satellite communication and remote sensing systems.

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.

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.

High continuous-wave power surface emitting terahertz lasers integrated with multimode interferometer

Distributed feedback (DFB) surface emitting semiconductor laser realizes power extraction by periodic photonic heterostructure. A direct method to increase the output power is scaling up the area of active region, however, the length of the device is restricted by the coupling strength of the DFB grating. Herein we develop a high-power single-mode surface emitting scheme by monolithically integrating second-order DFB terahertz quantum cascade laser and a multimode interferometer, which can significantly enhance the optical power by increasing photon density and altering field distribution in the grating region. Application of this concept leads to high continuous-wave (CW) surface emitting power of 55 mW, with single-lobed far-field pattern and single-mode operation at about 3.9 THz, which is among the best reported results. Such an integrated scheme can be combined with any one-dimensional photonic heterostructure, which has great potential in further improving the pulsed and CW output power of single-mode semiconductor lasers.

Power Scavenging Microsystem for Smart Contact Lenses.

On-the-eye microsystems such as smart contacts for vision correction, health monitoring, drug delivery, and displaying information represent a new emerging class of low-profile (≤ 1mm) wireless microsystems that conform to the curvature of the eyeball surface. The implementation of suitable low-profile power sources for eye-based microsystems on curved substrates is a major technical challenge addressed in this paper. The fabrication and characterization of a hybrid energy generation unit composed of a flexible silicon solar cell and eye-blinking activated Mg-O2 metal-air harvester capable of sustainably supplying electrical power to smart ocular devices are reported. The encapsulated photovoltaic device provides a DC output with a power density of 42.4 µW cm-2 and 2.5mW cm-2 under indoor and outdoor lighting conditions, respectively. The eye-blinking activated Mg-air harvester delivers pulsed power output with a maximum power density of 1.3mW cm-2. A power management circuit with an integrated 11 mF supercapacitor is used to convert the harvesters' pulsed voltages to DC, boost up the voltages, and continuously deliver ≈150 µW at a stable 3.3V DC output. Uniquely, in contrast to wireless power transfer, the power pack continuously generates electric power and does not require any type of external accessories for operation.

Domain-wall dark pulse generation with SMF-GIMF-SMF structure as artificial saturable absorber

We experimentally demonstrated the generation of domain-wall dark pulse in an Erbium-doped fiber laser using the combination of a 10 cm graded index multimode fiber sandwiched by single mode fibers as artificial saturable absorber. The interaction of phase difference in grade index multimode fiber allowed the stable dual-wavelength oscillation in the cavity. The dual-wavelength centered at 1567.2 nm and 1569.4 nm produces the topological defect in temporal domain and achieved a dark pulse formation with repetition rate of 21.5 MHz. The highest average pulse energy is calculated as 769.6 pJ with pulse width of 5 ns. Throughout the operating pump power range, the average pulse energy and output power increase linearly, with R2 of 0.9999 and achieved the laser efficiency of 9.33%. From the measurement in frequency domain, the signal-to-noise ratio is measured as 49 dB. As compared to reported DW dark pulse works, the proposed structure only required a short length of multimode fiber, which allowed the domain-wall dark pulse to achieve higher pulse repetition rate. The venture of domain wall dark pulse is potentially to pave the foundation toward sustainable industrial growth.

Analysis and Design of a Pulsed Power Generator for a Low-Energy Magnetic Pulse Welding System

Magnetic pulse welding (MPW) is a joining method that uses Lorentz force generated from an electromagnetic field. This method not only has the advantage of not causing thermal deformation of the material and no by-products compared to the method of joining by melting by heat but also enables the joining of dissimilar metals rather than the joining of the same metal. Joining dissimilar metals can reduce the weight of mechanical devices and apply them to various fields. Recent research on MPW has focused on the characteristics of bonding according to the material or structure of metal rather than on pulse power research that generates the main factor of operation. However, in the operation of MPW, a Lorentz force is generated by the induced current caused by the electromotive force created in the flyer tube and the external magnetic field in the actuator. Therefore, it is necessary to analyze and optimize the pulse power to improve reliability and to miniaturize the system to expand the MPW utilization range. In this paper, we analyzed MPW operation according to a section of the pulse power output waveform. A condition for obtaining the maximum current in the flyer tube was proposed, and a plateau-shaped waveform was derived as an ideal output waveform capable of maintaining the Lorentz force. Through analysis, the proposed pulse power device is designed as a pulse-forming network (PFN) that generates a plateau output waveform. The design specification is that the circuit of PFN (type E) is designed so that the output waveform is pulse width 10 (μs) and the maximum output current is 100 (kA), and it is verified by simulation.

Superpower X-Band Klystron with an Output Pulse Power of at Least 3 MW: Design and Experiment

Superpower X-Band Klystron with an Output Pulse Power of at Least 3 MW: Design and Experiment

Backscattered Background Noise of the Lidar Ceilometer Influence Imposed by ASE in Single-Frequency Nanosecond Pulsed Laser at 1.5 μm

In this work, we demonstrate a three-stage all-fiber master oscillator power amplifier (MOPA) system emitting over 1 W of the linearly polarized narrow-linewidth pulse output power with 10 kHz pulse repetition frequency and 400 ns pulse width without the amplified spontaneous emission (ASE) at ~1.5 µm. Initially, we analyze the effect of the ASE on the first derivative of backscatter intensity via a contrast experiment. The experiment results show that the noise intensity with angle of inclination is affected by the ASE of the amplifier, thereby decreasing the signal-to-noise ratio of the output power. The laser is characterized by a very low or no ASE level of the output signal when acquiring the first derivative of backscatter intensity with low noise. This condition provides a reference for improving the properties of the laser used for cloud detection.

Output Voltage Drop and Input Current Ripple Suppression for the Pulse Load Power Supply Using Virtual Multiple Quasi-Notch-Filters Impedance

To balance the instantaneous power difference between the pulsed output power and the constant input power of the pulse load power supply (PLPS), an active capacitor converter (ACC), which can compensate the pulsed current, is connected in parallel with the output of the dc-dc converter in the PLPS. In this paper, based on the Fourier decomposition results of the load current, it is evident that square waves have significant harmonic content. Hence, to provide the lower impedance at the frequencies of the high content harmonics in the load current, a virtual impedance that consisted of the multiple quasi-notch-filters (MQNF) is proposed to be in parallel at the port of the ACC for the suppression of output voltage drop and input current ripple. The virtual parallel impedance is implemented by the output voltage feedforward control (FFC) of the ACC. The design considerations of the virtual parallel impedance are presented to ensure the stability of the PLPS. Finally, a synchronous rectifier buck (SR-buck) converter with a bidirectional buck/boost converter is tested at the pulse repetition frequency (PRF) of 100-300 Hz and the pulse duty cycle of 0.15 to verify the validity of the proposed control scheme.

High-Power Acoustic-Optical Q-Switched 1.83 µm Tm-Doped Bulk Laser

We report on a high-power acoustic-optical (AO) Q-switched Tm:YLF laser operating at ~1.83 μm by controlling the transmittance of the output coupler. Under the continuous-wave (CW) operation, the maximum output power of 13 W is achieved, and the slope efficiency is up to 32.7%. With a YAG etalon inserted into the cavity, the linewidth is compressed below 0.5 nm with a maximum output power of 12.2 W. In the Q-switched state, the maximum pulsed output power of 10.32 W is achieved with a pulse duration of 150 ns when the repetition rate is 15 kHz. And the maximum pulsed energy of 1.13 mJ is generated with a duration of 131 ns at 5 kHz. As far as we know, this is the highest output power reported for the CW and pulsed 1.83 μm laser. In addition, the relationship between the output wavelength and crystal length is theoretically analyzed, which shows that increasing the loss of 1880 nm is the key to high-power 1.83 μm laser output.

Calibrating Data Mismatches in Deep Learning-Based Quantitative Ultrasound Using Setting Transfer Functions.

Deep learning (DL) can fail when there are data mismatches between training and testing data distributions. Due to its operator-dependent nature, acquisition-related data mismatches, caused by different scanner settings, can occur in ultrasound imaging. As a result, it is crucial to mitigate the effects of these mismatches to enable wider clinical adoption of DL-powered ultrasound imaging and tissue characterization. To address this challenge, we propose an inexpensive and generalizable method that involves collecting a large training set at a single setting and a small calibration set at each scanner setting. Then, the calibration set will be used to calibrate data mismatches by using a signals and systems perspective. We tested the proposed solution to classify two phantoms using an L9-4 array connected to a SonixOne scanner. To investigate generalizability of the proposed solution, we calibrated three types of data mismatches: pulse frequency mismatch, focus mismatch, and output power mismatch. Two well-known convolutional neural networks (CNNs), i.e., ResNet-50 and DenseNet-201, were trained using the ultrasound radio frequency (RF) data. To calibrate the setting mismatches, we calculated the setting transfer functions. The CNNs trained without calibration resulted in mean classification accuracies of around 52%, 84%, and 85% for pulse frequency, focus, and output power mismatches, respectively. By using the setting transfer functions, which allowed a matching of the training and testing domains, we obtained the mean accuracies of 96%, 96%, and 98%, respectively. Therefore, the incorporation of the setting transfer functions between scanner settings can provide an economical means of generalizing a DL model for specific classification tasks where scanner settings are not fixed by the operator.

Comparative study on passive Q-switching laser properties of Yb:CaWO4 and Yb:NaY(WO4)2 crystals

Yb:CaWO4 and Yb:NaY(WO4)2 are two tetragonal tungstates, possessing exactly the same crystal symmetry and local site symmetry for the Yb ion. In this work, a detailed comparison of spectroscopic properties was made between the two tungstates, showing a large degree of similarity in their polarized absorption and emission features. Stable passive Q-switching of an Yb:CaWO4 laser was demonstrated, generating 0.40 W of pulsed output power at 1024.7 nm at a repetition rate of 33 kHz; the resulting pulse energy, duration, and peak power were, respectively, 12.1 μJ, 50 ns, and 242 W. Compared to an Yb:NaY(WO4)2 laser operating under the same passive Q-switching conditions, while most of the output characteristics were similar, the pulse energy generated by the Yb:CaWO4 laser proved to be much higher. This may imply the greater potential of Yb:CaWO4 in generating high-energy laser pulses.

Efficient continuous-wave and passively Q-switched operation of an Yb:YPO4 microchip laser

We report on the performance of an Yb:YPO4 microchip laser that could be efficiently operated in both continuous-wave (CW) and passive Q-switching mode, with a 2D WS2 acting as the saturable absorber. With 6.30 W of pump power absorbed, a CW output power of 3.81 W was generated, leading to an optical conversion efficiency of 60.5%, while the slope efficiency amounting to 71%. In passively Q-switched operation, a pulsed output power of 1.67 W was produced at 660 kHz of repetition frequency, with a slope efficiency of 52%; the largest pulse energy, minimum pulse width, and highest peak power, which were achievable with different output mirrors, were respectively 2.52 μJ, 67 ns, and 31.7 W. The results demonstrated in this work represent a significant improvement in CW and passive Q-switching performance of Yb:YPO4 microchip lasers.

Novel RDD Pulse Shaping Method for High-Power High-Voltage Pulse Current Power Supply in DBD Application

High-voltage pulse power supplies are key power input devices for the study and application of discharge plasma. A high-voltage pulse current power supply (HV-PCPS) with an energy storage pulse transformer based on flyback topology can output microsecond pulsewidths with high-power, ultrahigh voltage, and high reliability, which are suitable for most dielectric barrier discharge (DBD) plasma applications. However, during the process of DBD driven by an HV-PCPS based on an energy storage pulse transformer, the output pulse voltage waveform quality is poor, making it not suitable for stable discharge long-term operation. This article aims to solve the aforementioned problem and proposes a novel resistor–diode–diode (RDD) shaping method. Not only can this novel method solve the problem of poor quality of the output pulse power from the HV-PCPS, guaranteeing stable discharge for various DBD electrodes, it can also limit the maximum output voltage amplitude. This prevents overvoltage breakdown when the output terminal is in an open state or a light load state because the HV-PCPS is acting as a current source. This article also analyzes the effectiveness of an RDD branch when solving the problem in theory, and gives a detailed parameter design method. Finally, a 30-kV HV-PCPS prototype is built to verify the effectiveness of the proposed RDD pulse shaping method. The average pulse power output of the whole prototype is greatly improved, and it can achieve an average pulse power output of 1 kW. Furthermore, the electrode loads of different DBD reactors can be driven by this technology.

∼8.5 μm-emitting InP-based quantum cascade lasers grown on GaAs by metal-organic chemical vapor deposition

Room-temperature, pulsed-operation lasing of 8.5 μm-emitting InP-based quantum cascade lasers (QCLs), with low threshold-current density and watt-level output power, is demonstrated from structures grown on (001) GaAs substrates by metal-organic chemical vapor deposition. Prior to growing the laser structure, which contains a 35-stage In0.53Ga0.47As/In0.52Al0.48As lattice-matched active-core region, a ∼2 μm-thick nearly fully relaxed InP buffer with strained 1.6 nm-thick InAs quantum-dot-like dislocation-filter layers was grown. A smooth terminal buffer-layer surface, with roughness as low as 0.4 nm on a 10 × 10 μm2 scale, was obtained, while the estimated threading-dislocation density was in the mid-range × 108 cm−2. A series of measurements, on lasers grown on InP metamorphic buffer layers (MBLs) and on native InP substrates, were performed for understanding the impact of the buffer-layer's surface roughness, residual strain, and threading-dislocation density on unipolar devices such as QCLs. As-cleaved devices, grown on InP MBLs, were fabricated as 25 μm × 3 mm deep-etched ridge guides with lateral current injection. The results are pulsed maximum output power of 1.95 W/facet and a low threshold-current density of 1.86 kA/cm2 at 293 K. These values are comparable to those obtained from devices grown on InP: 2.09 W/facet and 2.42 kA/cm2. This demonstrates the relative insensitivity of the device-performance metrics on high residual threading-dislocation density, and high-performance InP-based QCLs emitting near 8 μm can be achieved on lattice-mismatched substrates.

Passively Q-switched erbium doped fiber laser based on graphene and carbon nanotube saturable absorbers

A passively Q-switched erbium-doped fiber laser (EDFL) was experimented on by employing graphene, single walled carbon nanotubes (SWCNT) and multi-walled carbon nanotube (MWCNT) saturable absorbers (SA). The SA film was obtained by embedding the graphene, SWCNT and MWCNT into polyvinyl alcohol (PVA). The graphene SA was prepared by dipping a PVA thin film into the graphene solution while carbon nanotubes SAs were prepared using the casting method and placed in the ring cavity to produce a stable pulse laser. Graphene, SWCNT and MWCNT SAs were operating at wavelengths of 1558.92 nm, 1557.98 nm and 1558.51 nm, respectively, whereas the continuous wave was 1560.72 nm at the input pump power of 56 mW. The pulse energy, output power, repetition rate and pulse width were compared in graphene, SWCNT and MWCNT SAs. The shortest pulse width retrieved in graphene, SWCNT and MWCNT were 3.90 µs, 3.62 µs 4.43 µs and produced at the repetition rate of 115.00 kHz, 130.70 kHz, and 89.13 kHz, respectively. In comparison to graphene and SWCNT SAs, MWCNT SAs exhibit the best performance in terms of output power of 2.19 mW and high pulse energy of 24.57 nJ in passively Q-switched EDFL.