Pulse Shaping Capabilities Research Articles

Stationary High-Energy Pulse Generation in Er-Based Fiber Lasers via Quasi-Synchronous Gain Modulation

We demonstrate the feasibility of triggering stationary high-energy pulse generation in Er-doped fiber lasers at ~1.5 µm via quasi-synchronous gain modulation. This simple method relies upon the sine-wave modulation of pump power at a frequency slightly surpassing the intrinsic frequency spacing of longitudinal modes in the laser cavity. This was previously implemented only in Yb-doped fiber lasers at ~1.1 µm. Here, for the first time, we experimentally validate the pulse shaping capabilities of this method also in Er fiber lasers, which, unlike Yb fiber lasers, have a three-level laser energy diagram (when pumped at 0.98 µm) with a very long-lived (10 ms) upper laser level. The feasibility of the method was validated both for normal and anomalous intracavity dispersion, which was not available in previous implementations in Yb fiber lasers at ~1.1 µm. Thus, the stable generation of a regular train of discrete nanosecond pulses with an energy of up to 180 nJ was achieved in our test-bed Er fiber laser upon the quasi-synchronous sine-wave modulation of the pump power at 0.98 µm. The results of our study testify to the general applicability of this affordable and reliable method for high-energy pulse generation in various rare-earth-doped fiber lasers.

A High-Voltage Series-Stacked IGBT Switch With Output Pulse Shaping Capability to Reduce EMI Generation

A High-Voltage Series-Stacked IGBT Switch With Output Pulse Shaping Capability to Reduce EMI Generation

Overview of SwissFEL dual-photocathode laser capabilities and perspectives for exotic FEL modes

Abstract SwissFEL is a compact, high-brilliance, soft and hard X-ray free electron laser (FEL) facility that started user operation in 2019. The facility is composed of two parallel beam lines seeded by a common linear accelerator (LINAC), and a two-bunch photo-injector. For the injector, an innovative dual-photocathode laser scheme has been developed based on state-of-the-art ytterbium femtosecond laser systems. In this paper, we describe the performance of the SwissFEL photocathode drive lasers (PCDLs), the pulse-shaping capabilities as well as the versatility of the systems, which allow many different modes of operation of SwissFEL. The full control over the SwissFEL electron bunch properties via the unique architecture of the PCDLs will enable in the future the advent of more-advanced FEL modes; these modes include, but are not restricted to, the generation of single or trains of sub-femtosecond FEL pulses, multi-color FEL and finally, the generation of fully coherent X-ray pulses via laser-based seeding.

A Fully Integrated Programmable 6.0–8.5-GHz UWB IR Transmitter Front-End for Energy-Harvesting Devices

Ultra-wideband impulse radio transceivers are becoming a key building block for establishing ultralow power wireless sensor networks. However, impulse radio transmitters commonly suffer from a low spectral quality and a coarse frequency tuning resolution, which limits their global applicability. In this article, we present a fully integrated ultralow power impulse radio transmitter front-end (TFE) whose pulse shaping capabilities and integrated output matching network make it globally applicable up to a 4-MHz pulse repetition rate. We demonstrate a digital carrier frequency-tuning method that achieves a 28-MHz resolution over the frequency band of 6.0–8.5 GHz. In addition, we show that the temperature dependence of the TFE’s carrier frequency can be compensated digitally over the industrial temperature range from −40°C to 85 °C. The proposed TFE supports energy-harvesting applications particularly well due to its low leakage power level of 380 nW and a high tolerance to power supply transients during pulse generation. It is demonstrated to operate robustly with low-drive regulators powered by low-quality sources. The TFE is fabricated in a 65-nm CMOS process. It generates 1.8-pJ pulses at a 7.5-GHz carrier frequency while consuming 63 pJ per pulse, corresponding to 2.3% efficiency.

Generation and characterization of tailored MIR waveforms for steering molecular dynamics.

The dream of physico-chemists to control molecular reactions with light beyond electronic excitations pushes the development of laser pulse shaping capabilities in the mid-infrared (MIR) spectral range. Here, we present a compact optical parametric amplifier platform for the generation and shaping of MIR laser pulses in the wavelength range between 8 μm and 15 μm. Opportunities for judiciously tailoring the electromagnetic waveform are investigated, demonstrating light field control with a spectral resolution of 59 GHz at a total spectral bandwidth of 5 THz. In experiments focusing on spectral amplitude manipulation these parameters result in a time window of 1.8 ps available for shaping the temporal pulse envelope and a phase modulation resolution of 100 mrad for several picosecond delays.

Numerical Study of Magnetically Driven Isentropic Compression Experiments on PTS

The most powerful pulse power generator in China—primary test stand (PTS)—was used to get isentropic compression of aluminum to about 100 GPa. The high performance of synchronization system enables to trigger 24 modules according to a required timing sequence, which makes PTS a good platform for electromagnetically driven high energy density physics experiments. Two shots were used to establish the pulse-shaping capability and test the reliability of a numerical code. The first shot used a stripline load driven by a smooth rising current, while the second one was driven by a current with a weak start followed by a sharp rise. The current profiles, as well as the sample thicknesses, are optimized by a 1-D magneto-hydrodynamic code MADE1D, coupled with a full circuit model for PTS. The experimental setup, physical model, and simulation results are introduced. Comparing with the experimental results, simulated velocities at Al/LiF interface agree well with the measurement. It is shown that the shape of current pulse is one of the most important factors that impact the loading process.

Radiation Damage Tests on Diamond and Scintillation Detector Components for the ITER Radial Neutron Camera

During the International Thermonuclear Experimental Reactor (ITER) reactor operation time, the plasma will give rise to high energy neutron and gamma flux, and this intense radiation field will result in serious radiation damage and activation effects on various detectors components. In this paper, neutron detector candidates for the ITER radial neutron camera (RNC), i.e., scintillator components [crystal and plastic scintillators, optical windows, and photomultipliers (PMTs)] and single-crystal diamond detectors, were investigated to establish their radiation hardness and stability under gamma irradiation. Radiation test was carried out at the Italian National Agency for New Technologies, Energy and Sustainable Economic Development Calliope plant (Casaccia R.C., Rome, Italy). The facility is a pool-type irradiation plant equipped with a 60Co source (energy = 1.25 MeV). Gamma radiation tests were performed in the dark and at room temperature for different total absorbed doses, as required for the application in ITER RNC. Scintillators, PMTs, and optical windows were irradiated up to around 100-kGy absorbed dose, while single-crystal diamond detectors up to around 5 MGy. Scintillators and optical windows transmittance measurements were performed in the UV-VIS range (300–700 nm), paying particular attention to the behavior at 390 and 420 nm (scintillating emission wavelengths). Samples were measured in the dark before and after irradiation and their performances were monitored at room temperature for some weeks in order to study the damage recovery in different conditions. For plastic scintillators, photobleaching and optical bleaching followed by thermal annealing processes in air were made to reduce the radiation damage. Quantum efficiency measurements were performed on the PMTs, and the pulse-height spectra and pulse shape capability of the scintillators were investigated by using gamma and neutron sources. The most relevant results of this paper concern the radiation damage observed in scintillators and diamond detectors. The crystalline scintillator sample showed much less radiation resistance than plastic scintillators. A strong damage to the silver deposition of the diamond contacts was observed already at 1.0 MGy, almost leading to contact destruction at 4.7 MGy.

High-energy Nd:YAG laser system with arbitrary sub-nanosecond pulse shaping capability.

We report on a laser system capable of generating high-energy (>270 mJ) temporally shaped pulses at 1064 nm with 0.43-ns shaping resolution. The pulses are generated by modulation of a continuous-wave seed laser and subsequent amplification by a dual-stage grazing-incidence Nd:YVO4 "bounce" amplifier and a Nd:YAG power amplifier (all quasi-continuous diode-pumped). The system produces pulses with a high-quality top-hat spatial beam profile with up to 0.6 GW of peak power and 44 W of average power, a power stability of 0.22% rms, and fully programmable complex temporal shapes.

A 100 MHz PRF IR-UWB CMOS Transceiver With Pulse Shaping Capabilities and Peak Voltage Detector

This paper presents a high-rate IR-UWB transceiver chipset implemented in a 130-nm CMOS technology for WBAN and biomedical applications in the 3.1–4.9 GHz band. The transmitter is based on a pulse synthesizer and an analytical up-converted Gaussian pulse is used to predict its settings. Its measured peak-to-peak output voltage is equal to $0.9~V_{\mathrm{ pp}}$ on a 100 $\Omega $ load for a central frequency of 4 GHz, and a supply voltage of 1.2 V, which gives an emitted energy per pulse of 0.64 pJ. The receiver is a non-coherent architecture based on an LNA followed by a peak-voltage detector. A BER of 10−3 is measured for a 3.1–4.9 GHz input peak-to-peak pulse amplitude of 1.1 mV, which corresponds to a sensitivity of −85.8 dBm at 1 Mb/s and gives a communication range estimated to 1.9 m.

Temporal pulse precisely sculpted millijoule-level fiber laser injection system for high-power laser driver.

A fiber laser injection system used as a seeder for a high-power laser facility of inertial confinement fusion was designed to meet stringent requirements. Herein, we demonstrate the fiber laser injection system, whose output single-pulse energy reaches the millijoule class. With two-stage amplitude modulators, the system produces a pulse with a higher pulse shaping capability. In addition, amplifying the pulse with large-mode-area fiber and single polarization, large-mode-area photonic crystal fiber (PCF) ensures a good beam quality output. In this proof-of-principle experiment, the long-term stability of FM-to-AM modulation and pulse energy is demonstrated. The successful demonstration of this laser injection system holds great significance for future high-power laser drivers.

Femtosecond pulse shaping using wavelength-selective directional couplers: proposal and simulation.

The femtosecond pulse-shaping capabilities of wavelength-selective directional couplers are investigated. Numerical results show that, depending on the coupling length and coupling coefficient, one can achieve very different temporal shapes at the output of the directional couplers. For instance, temporal re-shaping of Gaussian-like pulses into Hermite-Gaussian pulses, parabolic pulses, square temporal waveforms and sequences of equalized multiple pulses with time widths down to the femtosecond range can be achieved using readily feasible fiber/waveguide designs. The detrimental influence of the second-order variation of the detuning factor in these pulse shapers is also numerically investigated.

Terahertz waveform generation for S21-parameter measurements using a fiber-coupled optical pulse shaper.

A THz time-domain spectroscopy-based vector network analyzer for S21-parameter measurements is presented providing THz waveforms as input signal for waveguide-coupled devices under test. We integrate an optical pulse shaper into the emitter arm and fiber-couple the photoconductive antennas to allow for flexible usage. The pulse-shaping capabilities are demonstrated by realizing all 5 bit combinations of a 0.5 THz signal. Furthermore, we can set the center wavelength of the resulting THz spectrum. Finally, we apply the shaped THz waveforms to test the response of a low-noise amplifier.

DiPOLE: a 10 J, 10 Hz cryogenic gas cooled multi-slab nanosecond Yb:YAG laser.

The Diode Pumped Optical Laser for Experiments (DiPOLE) project at the Central Laser Facility aims to develop a scalable, efficient high pulse energy diode pumped laser amplifier system based on cryogenic gas cooled, multi-slab ceramic Yb:YAG technology. We present recent results obtained from a scaled down prototype laser system designed for operation at 10 Hz pulse repetition rate. At 140 K, the system generated 10.8 J of energy in a 10 ns pulse at 1029.5 nm when pumped by 48 J of diode energy at 940 nm, corresponding to an optical to optical conversion efficiency of 22.5%. To our knowledge, this represents the highest pulse energy obtained from a cryo cooled Yb laser to date and the highest efficiency achieved by a multi-Joule diode pumped solid state laser system. Additionally, we demonstrated shot-to-shot energy stability of 0.85% rms for the system operated at 7 J, 10 Hz during several runs lasting up to 6 hours, with more than 50 hours in total. We also demonstrated pulse shaping capability and report on beam, wavefront and focal spot quality.

The Shock/Shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facility

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (∼ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment to the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.

High Power Diode-Seeded Fiber Amplifiers at 2 μm—From Architectures to Applications

We review recent advances in the development of high power short- and ultrashort pulsed Thulium-doped fiber amplifier (TDFA) systems seeded by semiconductor laser diodes at wavelengths around 2 μm. The diode-seeding and the master oscillator power amplifier (MOPA) design allow for the construction of extremely versatile laser systems that can operate over wide ranges of peak power, pulse energy and repetition rate in the ultrashort picosecond to the long nanosecond pulsed regimes. We present a record peak power of 130 kW and pulse energy of 5 μJ in picosecond mode, while demonstrating user-defined pulse-shaping capabilities at millijoule pulse energy levels in the nanosecond regime from essentially the same amplifier system. The system architecture as well as important design and power scaling considerations are discussed in detail. Additionally, we highlight recent results in the application of these MOPA systems and their high performance TDFA stages in such diverse application areas as next generation telecommunication networks, mid-infrared supercontinuum generation and mid-infrared gas detection in hollow-core photonic bandgap fibers.

National Security Research in Plasma Physics and Pulsed Power: Past, Present, and Future

The Naval Research Laboratory (NRL) was established in 1923 to fulfill Thomas Edison's vision of a government research laboratory that could develop and translate scientific knowledge into effective military systems in times of war. The NRL Plasma Physics Division was established in 1966 to create X-ray simulators for testing the effects of nuclear weapons on materials and components of military hardware, to study the physics and effects of high-altitude nuclear explosions, and to perform nuclear fusion research. This paper traces the development of pulsed power and plasma physics from 1940 to the present day through a set of graphical timeframes that depict both the major geopolitical events and the major pulsed power facilities that were noteworthy in a series of 15–20 year epochs. Pulsed power research began at the U.K. Atomic Weapons Establishment, where it was first used for radiography. Subsequently, Sandia, Los Alamos, and Livermore performed pulsed power research for an expanding set of missions. The earliest facilities consisted mostly of single-module machines that had limited ability to synchronize and pulse shape. The 1983 Strategic Defense Initiative led to the development of technologies for directed energy weapons, railguns, and X-ray lasers. The cessation of nuclear testing in 1992 created an increased need for above ground testing including advanced radiography, nuclear weapons effects simulators, hydrotest facilities, and inertial confinement fusion devices. The Stockpile Stewardship Program, which began in the mid-1990s, saw the construction of several major facilities [e.g., National Ignition Facility, Z, Omega, and DAHRT], with increased power, as well as sophisticated synchronization and pulse shaping capabilities. In 2012, the Department of Defense (DoD) announced a strategic pivot to the joint force of 2020 and a rebalance toward the Asian-Pacific region. Looking to the future, a number of DoD documents describe the need to develop and deploy transformational technologies. For example, the 2012 Naval S&T Strategic Plan emphasizes hypervelocity railguns, DE, the detection and neutralization of weapons of mass destruction, and the ability to retain access in contested environments, especially in space. Future military systems will require pulsed power that is compact, repetitive, efficient, and is thermally managed. Low-temperature plasmas and nonequilibrium plasma chemistry are emerging research areas that could impact DoD missions. Atmospheric plasmas are creating new opportunities in plasma biology and plasma medicine. The research capabilities of the rest of the world, especially China, are rapidly growing, and new ideas and capabilities will increasingly come from outside of the U.S. This paper explores some of the future challenges and opportunities for plasma physics and pulsed power research.

High-energy diode-seeded nanosecond 2 μm fiber MOPA systems incorporating active pulse shaping

We report on high-energy nanosecond-pulsed fiber master oscillator power amplifier (MOPA) systems seeded by semiconductor laser diodes at 2μm incorporating arbitrary pulse-shaping capabilities. Two MOPA systems, one based on direct diode modulation and the second using additional electro-optic modulator (EOM) based shaping, are investigated, with up to 0.5mJ (25kHz) and 1.0mJ (12.5kHz) pulse energies achieved, respectively, for 100ns pulses with user-defined pulse shapes. Our results indicate that further energy scaling with shaped output pulses is primarily limited by the maximum pulse peak power available from the seed laser diode and the dynamic range offered by the first generation of EOMs at 2μm.

Beryllium liner implosion experiments on the Z accelerator in preparation for magnetized liner inertial fusion

Multiple experimental campaigns have been executed to study the implosions of initially solid beryllium (Be) liners (tubes) on the Z pulsed-power accelerator. The implosions were driven by current pulses that rose from 0 to 20 MA in either 100 or 200 ns (200 ns for pulse shaping experiments). These studies were conducted in support of the recently proposed Magnetized Liner Inertial Fusion concept [Slutz et al., Phys. Plasmas 17, 056303 (2010)], as well as for exploring novel equation-of-state measurement techniques. The experiments used thick-walled liners that had an aspect ratio (initial outer radius divided by initial wall thickness) of either 3.2, 4, or 6. From these studies, we present three new primary results. First, we present radiographic images of imploding Be liners, where each liner contained a thin aluminum sleeve for enhancing the contrast and visibility of the liner's inner surface in the images. These images allow us to assess the stability of the liner's inner surface more accurately and more directly than was previously possible. Second, we present radiographic images taken early in the implosion (prior to any motion of the liner's inner surface) of a shockwave propagating radially inward through the liner wall. Radial mass density profiles from these shock compression experiments are contrasted with profiles from experiments where the Z accelerator's pulse shaping capabilities were used to achieve shockless (“quasi-isentropic”) liner compression. Third, we present “micro-Ḃ” measurements of azimuthal magnetic field penetration into the initially vacuum-filled interior of a shocked liner. Our measurements and simulations reveal that the penetration commences shortly after the shockwave breaks out from the liner's inner surface. The field then accelerates this low-density “precursor” plasma to the axis of symmetry.

Demonstration of Radiation Pulse-Shaping Capabilities Using Nested Conical Wire-Array $Z$-Pinches

We present data from experiments using nested wire-array Z -pinches where the wires of one of the arrays (the outer or inner array) are inclined to produce a cone. The use of these nested conical arrays can potentially provide a valuable tool in X-ray radiation pulse shaping for Z-pinch-driven high-yield inertial-confinement-fusion schemes. Conical nested arrays can produce a zippered implosion which broadens the main radiation pulse and, possibly, the pulse associated with the interaction of the two arrays. Results from experiments at current levels of 1 MA (240 ns) and 18 MA (100 ns) are presented and compared. Experiments at 1 MA with a conical outer array indicate broadening of the full-width at half-maximum of the main stagnation radiation pulse, with results at 20 MA showing a similar result. Conical inner arrays do not broaden the main radiation pulse because a longer inner array ablation time offsets the earlier interaction time of the outer array with the inner array. Although array dynamics data suggest that a conical inner or outer array can potentially provide control of the interaction radiation pulse, this was not observed. Observations are consistent with a wire-array trajectory model incorporating outer and inner array ablation, snowplow physics, and a simplified array interaction model.

Spatially dispersive scheme for transmission and synthesis of femtosecond pulses through a multicore fiber

A new scheme is presented for fiber transmission of ultrashort laser pulses. A dispersive device divides the input pulses into spatially separated spectral components which are individually launched in the different channels of a multicore fiber before being recombined at the output by a second dispersive device. The parallel transmission of narrow spectral bands avoids self-phase modulation and could be appropriate to deliver high peak power pulses. Phase management of the spectral bands by an active element offers recovery of the seed pulse duration at the fiber output as well as pulse shaping capabilities. Both are reported in a proof of concept experiment using 190 fs input pulses and a 5 cores polarization maintaining fiber. Extension of the concept to femtosecond pulses amplification is suggested.