Subnanosecond Duration Research Articles

Enhancing conversion efficiency of MgO:PPLN and Rb:PPKTP crystal-based subnanosecond optical parametric generators by utilizing a supercontinuum seed

This paper presents an approach to enhance the conversion efficiency of subnanosecond pulse duration microlaser-pumped optical parametric generators (OPGs) tunable from near- to mid-infrared. The method involves generating a supercontinuum (SC) in the photonic crystal fiber (PCF) and using it to seed the subnanosecond OPG based on the fan-out grating design MgO:PPLN crystal. Since the SC spectrum covered the entire signal wave tuning range (1414–2128 nm), seeding and conversion efficiency improvement of 6%–11% was achieved for all OPG signal wavelengths, and the generation threshold was reduced up to 3 times. Such a method allows for improved energy stability, significantly increases the brightness of the OPG output radiation, and is pivotal in mitigating the risk of MgO:PPLN optical damage. The study also extended the method to successfully seed 532 nm pumped Rb-doped PPKTP crystal-based OPG with the same SC, demonstrating broad applicability and performance improvement across different parametric devices.

A High-Power Source of Ultrawideband Radiation of Subnanosecond Duration with Controllable Characteristics

A High-Power Source of Ultrawideband Radiation of Subnanosecond Duration with Controllable Characteristics

DIRECT EXPERIMENT ON THE PASSAGE OF ULTRA-WIDEBAND PULSES OF SUBNANOSECOND DURATION IN THE EARTH’S ATMOSPHERE

The results of the first direct experiments on the passage of pulses of ultra-wideband radiation of subnanosecond duration in the Earth’s atmosphere at a distance of more than 10 km are presented. In contrast to the calculated work, the preservation of the amplitude-time shape of the pulses in the process of increasing the distance is shown. The establishment of this fact is of decisive importance in the practical application of ultra-wideband pulses in new technological developments.

A Direct Experiment on the Passage of Ultra-Wideband Pulses of Subnanosecond Duration in the Earth’s Atmosphere

A Direct Experiment on the Passage of Ultra-Wideband Pulses of Subnanosecond Duration in the Earth’s Atmosphere

Sub-nanosecond, 41 mJ pulse energy, passively Q-switched Nd:YLF laser

A sub-nanosecond, diode-stack side-pumped, passively Q-switched Nd3+:YLF4/Cr4+:YAG Laser is reported in a compact cavity design, generating one pulse of 41 mJ with a pulse width of 894 ps, achieving a peak output power of 46 MW and beam quality M2 of 5.4 × 5.9 (HxV). The number of pulses in the pulse train could be adjusted from one pulse to ten pulses of 111 mJ total output energy and 23.7 % optical efficiency by adjusting the focus distance while maintaining sub-nanosecond pulse duration. This resonator can also be used for high-power simultaneous Q-switched laser emission at 1047 nm and 1053 nm.

Determination of Shielding Effectiveness of a Subnanosecond High-Power EM Interference by an Enclosure with Aperture Using Time Domain Approach

Determination of Shielding Effectiveness of a Subnanosecond High-Power EM Interference by an Enclosure with Aperture Using Time Domain Approach

Sub-nanosecond diode-pumped passively Q-switched Nd:LuAG ceramic microchip lasers

Diode-pumped continuous-wave and passively Q-switched Nd:LuAG ceramic microchip lasers at 1064 nm and 1053 nm have been demonstrated, for the first time to our knowledge. For the continuous-wave operation, the achieved maximum output powers of the two lasers reaches 1.62 W and 0.75 W, respectively. Using Cr:YAG crystal as saturable absorber, the two lasers can also been operated in passively Q-switched regimes with sub-nanosecond pulse durations of 489 ps and 556 ps, respectively. The maximum single pulse energy and pulse peak power for the 1064 nm and 1053 nm lasers are calculated to be about 22.25 μJ and 45.49 kW, as well as 12.74 μJ and 22.91 kW. All solid-state microchip lasers give the tremendous potential for high performance laser generation with sub-nanosecond short pulse duration, high single pulse energy and high pulse peak power.

Analyzing the filamentation of MeV-range proton bunches in a laser-driven ion beamline and optimizing their peak intensity

In this article, we report on the latest investigations and achievements in proton beam shaping with our laser-driven ion beamline at GSI Helmholtzzentrum f\"ur Schwerionenforschung GmbH. This beamline was realized within the framework of the Laser Ion Generation, Handling, and Transport (LIGHT) collaboration to study the combination of laser-driven ion beams with conventional accelerator components. At its current state, the ions are accelerated by the high-power laser PHELIX via target normal sheath acceleration, and two pulsed high-magnetic solenoids are used for energy selection, transport, and transverse focusing. In between the two solenoids, there is a rf cavity that gives the LIGHT beamline the capability to longitudinally manipulate and temporally compress ion bunches to sub-nanosecond durations. To get optimal results, the rf cavity has to be synchronized with the PHELIX laser and therefore a reliable measurement of the temporal ion beam profile is necessary. In the past, these measurements showed unexpected correlations between the temporal beam profile and the phase as well as the electric field strength of the cavity. In this article, we present a numerical simulation of the beam transport through the LIGHT beamline which explains this behavior by a beam filamentation. We also report on our latest experimental campaigns, in which we combined transverse and longitudinal focusing for the first time. This led to proton bunches with a peak intensity of $(3.28\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}{10}^{8}\text{ }\text{ }\mathrm{protons}/({\mathrm{ns}\text{ }\mathrm{mm}}^{2})$ at a central energy of ($7.72\ifmmode\pm\else\textpm\fi{}0.14$) MeV. The intensity refers to a circle with a diameter of ($1.38\ifmmode\pm\else\textpm\fi{}0.02$) mm that encloses 50% of the protons in the focal spot at the end of the beamline. The temporal bunch width at this position was ($742\ifmmode\pm\else\textpm\fi{}40$) ps (FWHM).

Multi-frame multi-exposure shock wave imaging and pressure measurements.

Shock wave visual detection was traditionally performed using streak cameras, limited to homogeneous shock wave emission, with the corresponding shock wave pressure measurements available at rather large distances or numerically estimated through equation of state for water. We demonstrate a multi-frame multi-exposure shock wave velocity measurement technique for all in-plane directions of propagation, based on custom-built illumination system allowing multiple illumination pulses within each frame at multi-MHz frame rates and at up to 200 MHz illumination pulse repetition frequency at sub-nanosecond pulse durations. The measurements are combined and verified using a fiber-optic probe hydrophone, providing independent shock wave pressure and time-of-flight measurements, creating a novel all-optical measurement setup. The measured pressures at distances around 100 µm from the plasma center exceed 500 MPa, while camera-based measurements at even shorter distances indicate pressures above 1 GPa.

Регенеративная система в пассивной радиосенсорной технической диагностике электронных устройств

This work is devoted to the problem of processing signal radio profiles with a duration of less than 1 ns. These radio profiles are obtained by registering the electrical component of the near field of electromagnetic radiation induced by the electronic unit of the device using the method of passive radio engineering diagnostics. The reasons for the occurrence of significant errors in the processing of signal radio profiles by modern methods of direct analog-to-digital conversion and parallel conversion of real time are shown, associated with a decrease in the number of effective bits, an increase in sampling irregularity and signal rise time. A method is proposed for reducing the arising errors by switching to the method of stroboscopic scale-to-time transformation using multiple repro duction (regeneration) of a complex signal section by means of the previously presented regenerative system. Numerical modeling of the functioning of the regeneration system together with a stroboscopic time-scale converter was carried out in the study of the area of interest in the signal radio profile in the Simulink environment of the MatLab package. Using the correlation analysis of the reconstructed and the original signal radio profile, the validity of the use of the regenerative system in the processing and recovery of signal radio profiles of subnanosecond duration is shown. An experiment was prepared and carried out using modern high-speed equipment: a real-time oscilloscope and a stroboscopic oscilloscope with a subpicosecond sampling to study the correctness of the applicability of the regeneration method when combining the scale-time transformation and real-time transformation. The result of the stroboscopic scale-to-time transformation in the equivalent time mode with the transfer of the section to the general signal reconstructed in real time is presented. It is concluded that the accuracy of processing the original signal is increased by means of regeneration followed by restoration by methods of stroboscopic scale-time transformation, which allows further analysis of the signal radio profile with the smallest errors. Also, the regeneration system together with the strobe-frame-sampler can be used as a hardware method for conducting passive radiosensor technical diagnostics.

Highly stable sub-nanosecond Nd:YAG pump laser for optically synchronized optical parametric chirped-pulse amplification.

We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only <0.2% (rms). With an external LBO doubler, the system generated 330 ps green pulse energy of 130 mJ at 532 nm with a conversion efficiency of 65%. The pulse duration was further extended to 490 ps by adjusting Nd:YAG crystal temperature. To the best of our knowledge, these results present a longer pulse duration with higher stability than previous Nd:YAG lasers with sub-nanosecond optical synchronization.

High-energy pulses from all-PM ultra-long Yb-fiber laser mode-locked with quasi-synchronous pumping

We explore, for the first time, mode-locking capabilities and frontiers of a quasi-synchronous pumping technique implemented in an all-polarization-maintaining (all-PM) kilometer-long Yb-fiber laser. This technically simple approach to synchronous pumping relies on sine-wave modulation of pump power at a frequency slightly detuned from the laser cavity inter-mode frequency or its multiple. In combination with the scaled-up all-PM-fiber cavity, it has provided stable generation of linearly polarized (scalar) high-energy (up to 130 nJ) pulses with tunable nanosecond duration at the fundamental and harmonic repetition rates ranging from 0.23 to 0.69 MHz. The obtained combination of such a low repetition rate, such a high energy level, and polarization stability is unique for actively mode-locked all-fiber stimulated-emission-based master oscillators. We reveal that detuning of the pump modulation frequency is the key parameter for the pulse shaping control in such mode-locked laser, and further intracavity pulse shortening towards sub-nanosecond duration is theoretically possible with measures preventing pulses from accumulation of excessive nonlinear phase. The demonstrated approach opens up new prospects for pump-modulation-based mode locking in diode-pumped lasers with such inertial active media as rare-earth-doped fibers.

Stable Subnanosecond Passively Q-Switched Laser End-Pumped by Intense Pulse with Compact Design

We demonstrate a stable compact passively Q-switched laser generating 40 μJ, subnanosecond (< 1 ns) duration, 1064 nm pulses at a repetition rate of 10 kHz. With a composite Nd:YAG/Cr4+:YAG crystal in a simple and compact resonator end-pumped by intense 808 nm pulse, we effectively improve the stability of output laser pulses corresponding to the interpulse amplitude instability less 1% (rms) and the period jitter less 1 μs. These measured pulse-time characteristics agree with numerical simulations and the beam is close to the diffraction limit, with M2 < 1.2. The excellent optical properties and structure make this laser to be an attractive source for high-resolution 3D imaging radars or other widespread applications.

First on-line detection of radioactive fission isotopes produced by laser-accelerated protons

The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi-hbox {MeV} photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around 100 , hbox {MeV}, the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of 200 , hbox {J} at approx , 500 , hbox {fs} duration from the PHELIX laser produced more than 10^{12} protons with energies above 15 , hbox {MeV} in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the upgamma-rays were registered. The identified nuclides include those that have half-lives down to 39 , hbox {s}. These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities.

Characterization of sub-nanosecond pulsed laser amplification with Er:Yb co-doped phosphate glass fibers

We present an experimental characterization of the amplification of sub-nanosecond duration laser pulses at a wavelength of 1538 nm in short custom-made Er:Yb phosphate glass fibers with different core diameters. The fibers vary in their diameter from 100 µm (highly multi-mode) down to 12 µm (single-mode). The peak power, energy per pulse, and spectral shape of the amplified signal are presented. With our input pulses, the measurements show that the large core diameter fibers do not increase the amplification of the 1538 nm signal. We believe this is due to the high re-absorption of the Er3+ ions in the phosphate fiber. The optimal fiber geometry was found to have a core diameter of 20 µm with a length of 14 cm. The maximum peak power is 8.25 kW, corresponding to a net gain of 10.9 dB, with a pulse duration of 0.7 ns and a repetition rate of 40 kHz.

Experimental Observation of Ultrashort Hyperchaotic Dark Multisoliton Complexes in a Magnonic Active Ring Resonator.

We report on the self-generation of ultrashort hyperchaotic dark multisoliton sequences with two positive large Lyapunov exponents in an active ring resonator consisting of a multifunctional L-shaped magnonic waveguide and a saturable amplifier. The irregular magnonic waveguide supports the converting of backward volume magnetostatic spin waves with negative dispersion to magnetostatic surface spin waves with positive dispersion that is accompanied by a transition from four-wave to three-wave nonlinear spin-wave interactions. Each multisoliton complex consists of four dark parametric pulses containing the soliton trains of four dark incoherent spin-wave envelope solitons possessing a subnanosecond duration. Such patterns are formed due to the dispersion and nonlinearity management, the nonlinear transformation of the pulse signal in the saturable amplifier and the partial chaotic synchronization of both the ring eigenmodes and the spin wave automodulation frequencies. We also demonstrate a new intermittency type of "hyperchaotic multisoliton complexes-hyperchaotic multisoliton gas" with the increase of the signal power level.

Filamentation and Self-Focusing of Electron Beams in Vacuum and Gas Diodes

In this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the interaction of electrons with the anode are shown to develop in vacuum and gas diodes at nanosecond and subnanosecond durations of a beam current pulse and a decrease in the interelectrode gap. The average electron energy in filamentation and self-focusing of an electron beam in a vacuum diode of an accelerator at a current of ~2 kA and a no-load voltage of ~400 kV was established to be 50–100 keV while the energy density was 109–1010 J/cm3. It is confirmed that the beam current density in a gas diode can exceed 1 kA/cm2. It is hypothesized that superdense electron beams in vacuum and gas diodes are formed as a result of avalanche multiplication of runaway electrons in the cathode–anode gap plasma.

Generation of pulses with sub-nanosecond duration and sub-joule energy in gain-switched Ti: Sapphire lasers.

We realized the generation of pulses with a 460 ps duration, 1% pulse duration stability, and 300 mJ pulsed energy in a gain-switched Ti: Sapphire laser. We show that a flattening of the pumping beam profile and an increase of pump fluence up to the threshold of second pulse generation are the main conditions to achieve pulses with minimum duration and maximum stability. The negative influence of pump nonuniformity on laser characteristics was also studied. The maximum pulse energy was restricted by available pump energy of the nanosecond Q-switched Nd: YAG laser.

Филаментация и самофокусировка электронных пучков в вакуумных и газовых диодах

AbstractIn this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the interaction of electrons with the anode are shown to develop in vacuum and gas diodes at nanosecond and subnanosecond durations of a beam current pulse and a decrease in the interelectrode gap. The average electron energy in filamentation and self-focusing of an electron beam in a vacuum diode of an accelerator at a current of ~2 kA and a no-load voltage of ~400 kV was established to be 50–100 keV while the energy density was 10^9–10^10 J/cm^3. It is confirmed that the beam current density in a gas diode can exceed 1 kA/cm^2. It is hypothesized that superdense electron beams in vacuum and gas diodes are formed as a result of avalanche multiplication of runaway electrons in the cathode–anode gap plasma.

Nanosecond discharge in atmospheric pressure air with ectonic introduction of iron and copper vapor in plasma and its application in nanotechnology

Introduction: Nanosecond discharges in high-pressure gases between metal electrodes are promising for applications in selective UV lamps. The most investigated working media of such lamps are copper and iron vapors in the air, which are excited by a high-voltage discharge of subnanosecond duration. The use of various metal electrodes in one discharge gap and discharge excitation pulses with an amplitude of 20–40 kV and a duration of 50–100 ns is little studied, which is important for controlling the spectral characteristics of the lamp and producing complex oxide nanostructures based on two different metals. Also important is the use of such discharges for the synthesis of nanostructures of transition metal oxides in assisting the deposition process with hard UV radiation, which allows to improve some of their characteristics. Purpose: The aim of the work is to study the electrical and emission characteristics of a bipolar overstressed nanosecond discharge between stainless steel and copper electrodes in atmospheric pressure and to synthesize and study the optical characteristics of thin films deposited on a glass substrate from the sputtered products of metal electrodes in an air plasma. Methods : We used an optical spectroscopic method for studying the discharge plasma. Results : The results of a study of the electrical characteristics of overstressed nanosecond discharge in air at atmospheric pressure between stainless steel electrodes and copper and stainless electrodes found that it is a source of UV radiation from atoms and iron and copper ions in the spectral range 200-300 nm. The peak value of the electric power of the discharge is ~ 4 MW, and the energy contribution to the plasma per pulse was ~ 0.1 J. The developed point source of UV radiation based on the discharge between the copper and stainless electrode is promising for applications in medicine and sanitation. It has been established that under the assistantance by UV-radiation the developed “point” source in the nanostructures of iron oxides, enlightenment bands appear in the visible region of the spectrum. Conclusion: Experiments revealed the suitability of this discharge for use in a selective UV lamp on iron and copper vapor and deposition of nanostructured films based on iron oxides while assisting the process of deposition by UV radiation.