High Pulse Energy Research Articles

High-Energy Burst-Mode 3.5 μm MIR KTA-OPO

In this paper, a high energy 3.5 μm mid-infrared (MIR) burst-mode KTA optical parametric oscillator (OPO) was demonstrated. Utilizing a quasi-continuous wave (QCW) laser diode (LD) side-pump module and electro-optic (EO) Q-switching technique, a high beam quality 1064 nm burst-mode laser was achieved as the fundamental source, generating 30 mJ high-energy pulses at burst repetition rates of 100 Hz and 200 Hz with sub-burst repetition rates of 20 kHz, 40 kHz, and 50 kHz. The KTA-OPO produced a 3.5 μm MIR burst-mode laser output with 4 to 11 sub-pulses per pulse envelope. The output energies were 2.9 mJ, 2.81 mJ, and 2.79 mJ at 100 Hz, as well as 2.8 mJ, 2.75 mJ, and 2.72 mJ at 200 Hz, with corresponding conversion efficiencies of 9.6%, 9.3%, and 9.3% at 100 Hz, as well as 9.3%, 9.2%, and 9.1% at 200 Hz, respectively. Our results pave a new way for generating burst-mode MIR lasers.

Multimodal imaging of murine cerebrovascular dynamics induced by transcranial pulse stimulation.

Transcranial pulse stimulation (TPS) is increasingly being investigated as a promising potential treatment for Alzheimer's disease (AD). Although the safety and preliminary clinical efficacy of TPS short pulses have been supported by neuropsychological scores in treated AD patients, its fundamental mechanisms are uncharted. Herein, we used a multi-modal preclinical imaging platform combining real-time volumetric optoacoustic tomography, contrast-enhanced magnetic resonance imaging, and ex vivo immunofluorescence to comprehensively analyze structural and hemodynamic effects induced by TPS. Cohorts of healthy and AD transgenic mice were imaged during and after TPS exposure at various per-pulse energy levels. TPS enhanced the microvascular network, whereas the blood-brain barrier remained intact following the procedure. Notably, higher pulse energies were necessary to induce hemodynamic changes in AD mice, arguably due to their impacted vessels. These findings shed light on cerebrovascular dynamics induced by TPS treatment, and hence are expected to assist improving safety and therapeutic outcomes. ·Transcranial pulse stimulation (TPS) facilitates transcranial wave propagation using short pulses to avoid tissue heating. ·Preclinical multi-modal imaging combines real-time volumetric optoacoustic (OA) tomography, contrast-enhanced magnetic resonance imaging (CE-MRI), and ex vivo immunofluorescence to comprehensively analyze structural and hemodynamic effects induced by TPS. ·Blood volume enhancement in microvascular networks was reproducibly observed with real-time OA imaging during TPS stimulation. ·CE-MRI and gross pathology further confirmed that the brain architecture was maintained intact without blood-brain barrier (BBB) opening after TPS exposure, thus validating the safety of the procedure. ·Higher pulse energies were necessary to induce hemodynamic changes in AD compared to wild-type animals, arguably due to their pathological vessels.

130 μJ linear-polarized single-frequency 12-μm-core Er/Yb co-doped fiber amplifier based on pre-shaped seed pulse

<sec>Stimulated Brillouin scattering (SBS) is the major barrier in the process of energy scaling for pulsed single-frequency fiber master oscillator power amplifier (MOPA). Due to gain saturation effect, the laser pulse profile will be gradually distorted with the increase of pump power, which induces steep leading edge and narrower width for the amplified pulses. The resulting laser peak power would increase rapidly and thus the SBS threshold is reached earlier to limit the amplification of pulse energy.</sec><sec>A method to obtain high-energy pulsed single-frequency laser by pulse pre-shaping is demonstrated in this work. By designing the leading edge of the triangular pulse, optimizing its rising trend and the duration of the low-intensity rising part, the pulse width compression phenomenon caused by gain saturation is alleviated effectively. Thereafter, the laser peak power increase process can be retarded to reach the SBS threshold so that higher energy can be amplified for the pulsed single-frequency fiber laser. In the experiment, when the seed pulse is optimized to be a triangular pulse with a low-intensity rising edge of 401 ns and a pulse width of 520 ns, a linear-polarized pulse single-frequency fiber laser of 130.9 μJ is obtained in a 12-μm-core Er/Yb co-doped polarization-maintaining fiber. The pulse width is broadened to 608 ns at the maximum energy. When it is compared with the triangular pulse seed with a rapidly rising leading edge, its maximum energy is increased by about 25%. The optical signal-to-noise ratio and polarization extinction ratio are measured to be 42 dB and 16 dB at the maximum pulse energy, respectively. The corresponding spectral linewidth measured by a delayed self-heterodyne system is 542 kHz. Higher pulse energy can be anticipated by further optimizing the pulse profile and using large-mode-are gain fibers.</sec>

High-energy tunable ultraviolet pulses generated by optical leaky wave in filamentation

Ultraviolet pulses could open up new opportunities for the study of strong-field physics and ultrafast science. However, the existing methods for generating ultraviolet pulses face difficulties in fulfilling the twofold requirements of high energy and wavelength tunability simultaneously. Here, we theoretically demonstrate the generation of high-energy and wavelength tunable ultraviolet pulses in preformed gas-plasma channels via the leaky wave emission. The output ultraviolet pulse has a tunable wavelength ranging from 91 nm to 430 nm, and an energy level up to sub-mJ. Such a high-energy tunable ultraviolet light source may provide promising opportunities for characterization of ultrafast phenomena, and also an important driving source for the generation of high-energy attosecond pulses.

Platform for laser-driven X-ray diagnostics of heavy-ion heated extreme states of matter

We report on commissioning experiments at the high-energy, high-temperature (HHT) target area at the GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany, combining for the first time intense pulses of heavy ions from the SIS18 synchrotron with high-energy laser pulses from the PHELIX laser facility. We demonstrate the use of X-ray diagnostic techniques based on intense laser-driven X-ray sources, which will allow probing of large samples volumetrically heated by the intense heavy-ion beams. A new target chamber as well as optical diagnostics for ion-beam characterization and fast pyrometric temperature measurements complement the experimental capabilities. This platform is designed for experiments at the future Facility for Antiproton and Ion Research in Europe GmbH (FAIR), where unprecedented ion-beam intensities will enable the generation of millimeter-sized samples under high-energy-density conditions.

Lead-acid battery desulfation using a high-frequency pulse desulfator in standalone PV systems

The work presented in this article contributes to the study of a standalone photovoltaic (PV) system with battery storage by creating an electronic board that allows for the recovery of the battery's capacity using pulse technology that uses high-energy pulses from the PV panel to break down and remove the sulfation buildup, which is a contributing factor in the failure of most lead-acid batteries. Different methods or treatments can be used to lessen the impact of sulfation or even get rid of it and achieve battery rejuvenation. Battery sulfation is a process in which sulfate crystals form on the plates of a lead-acid battery, impeding its ability to retain a charge, and decreasing the battery’s overall effectiveness. This process can happen due to various reasons, such as charging for a shorter time than required, charging for a longer period of time than required, or even not charging it for quite some time. Sulfation affects a battery’s lifespan and comes with adverse effects on its performance, though it can be prevented.

Compact laser-diode-based optoacoustic mesoscopy.

Short-pulsed solid-state lasers (SSLs) are the most commonly employed light sources in optoacoustic imaging applications. However, their bulky size hinders compact and portable system implementations. Here we developed a compact laser diode (LD)-based optoacoustic mesoscopy (CoLD-OAM) scanner that employs a fiber-coupled laser diode source with 46 × 43 × 11 mm dimensions. CoLD-OAM features a scalable excitation pulse width in the 30-200 ns range, high pulse energies up to 6 µJ, and excellent pulse-to-pulse energy stability of 0.42%. Real-time imaging of the human wrist has been demonstrated with the system, achieving image quality similar to that of SSL-based systems. These advancements facilitate the development of portable optoacoustic systems with strong clinical translation and commercialization potential.

Theoretical analysis of the phase characteristics in few-cycle laser coherent beam combining

To meet the increasing demand for high-energy (Joule-level) few-cycle pulses in strong-field physics research, coherent beam combining (CBC) presents an effective method to further enhance the power of few-cycle pulse sources. However, due to the broad spectrum and ultrashort pulse duration of few-cycle pulses, achieving efficient beam combining is particularly challenging. In this paper, we employ the angular spectrum (ASM) method to numerically simulate the propagation of few-cycle pulses in a focusing system. By constructing a three-dimensional (2D + 1D) model, we accurately quantify the effects of laser parameters such as carrier-envelope phase (CEP) difference, time delay (TD), dispersion between beams, and combining configurations on the combining efficiency and CEP shift. The study results provide design guidelines for high energy few-cycle laser systems based on coherent beam combining and reveal the possibility to significantly enhance the combining efficiency while maintaining high CEP stability, which will finally provide a reliable light source for advancing the frontier of strong-field physics.

Mid-infrared photoacoustic brain imaging enabled by cascaded gas-filled hollow-core fiber lasers.

Extending the photoacoustic microscopy (PAM) into the mid-infrared (MIR) molecular fingerprint region constitutes a promising route toward label-free imaging of biological molecular structures. Realizing this objective requires a high-energy nanosecond MIR laser source. However, existing MIR laser technologies are limited to either low pulse energy or free-space structure that is sensitive to environmental conditions. Fiber lasers are promising technologies for PAM for their potential to offer both high pulse energy and robust performance, which however have not yet been used for PAM because it is still at the infant research stage. We aim to employ the emerging gas-filled anti-resonant hollow-core fiber (ARHCF) laser technology for MIR-PAM for the purpose of imaging myelin-rich regions in a mouse brain. This laser source is developed with a high-pulse-energy nanosecond laser at , targeting the main absorption band of myelin sheaths, the primary chemical component of axons in the central nervous system. The laser mechanism relies on two-order gas-induced vibrational stimulated Raman scattering for non-linear wavelength conversion, starting from a 1060-nm pump laser to through the two-stage gas-filled ARHCFs. The developed fiber Raman laser was used for the first time for MIR-PAM of mouse brain regions containing structures rich in myelin. The high peak power of and robust performance of the generated MIR Raman pulse addressed the challenge faced by the commonly used MIR lasers. We pioneered the potential use of high-energy and nanosecond gas-filled ARHCF laser source to MIR-PAM, with a first attempt to report this kind of fiber laser source for PAM of lipid-rich myelin regions in a mouse brain. We also open up possibilities for expanding into a versatile multiwavelength laser source covering multiple biomarkers and being employed to image other materials such as plastics.

On-chip petahertz electronics for single-shot phase detection

Attosecond science has demonstrated that electrons can be controlled on the sub-cycle time scale of an optical waveform, paving the way towards optical frequency electronics. However, these experiments historically relied on high-energy laser pulses and detection not suitable for microelectronic integration. For practical optical frequency electronics, a system suitable for integration and capable of generating detectable signals with low pulse energies is needed. While current from plasmonic nanoantenna emitters can be driven at optical frequencies, low charge yields have been a significant limitation. In this work we demonstrate that large-scale electrically connected plasmonic nanoantenna networks, when driven in concert, enable charge yields sufficient for single-shot carrier-envelope phase detection at repetition rates exceeding tens of kilohertz. We not only show that limitations in single-shot CEP detection techniques can be overcome, but also demonstrate a flexible approach to optical frequency electronics in general, enabling future applications such as high sensitivity petahertz-bandwidth electric field sampling or logic-circuits.

Stabilized 30 µJ dissipative soliton resonance laser source at 1064 nm

We demonstrate the first successful stabilization of a dissipative soliton resonance (DSR) mode-locked (ML) laser source using straightforward techniques. Our setup employed a figure-8 (F8) resonator configuration and a nonlinear optical loop mirror (NOLM) to achieve stable mode-locking, generating 1064 nm rectangular pulses with a 3 ns duration at a repetition frequency of ~ 1 MHz. The pulses were boosted in an all-fiber amplifier chain and reached 30 µJ and 10 kW peak power per pulse at 30 W average output power. We addressed a critical gap in the literature by actively stabilizing key DSR pulse parameters: average output power (improved by a factor of 51), pulse repetition frequency (improved by 7583 using cross-phase modulation for synchronization), and pulse duration (improved by a factor of ~ 4). Additionally, we included a numerical analysis to explore the pulse formation mechanisms in DSR ML lasers working in a F8 configuration. Our findings show that non-complex all-in-fiber DSR ML lasers can reliably produce high-energy pulses with stable, repeatable parameters, making them suitable for future applications e.g. in nonlinear frequency conversion, laser micromachining, or LIDAR.

2-µm energy-managed soliton fiber laser.

To generate energetic short pulses from fiber laser oscillators in the 2-µm emission window, we here propose an alternative to the conventional methods of pulse stretching and dispersion management. We build a passively mode-locked fiber laser from anomalous single-mode fibers and utilize strong dissipative effects to delineate high and low pulse energy sections within the cavity. Whereas the main laser output delivers low-chirp sub-ps pulses with an energy up to 12 nJ, the intracavity pulse is reshaped into a ∼0.1-nJ conventional soliton, stabilizing the laser dynamics while enabling a wide tunability in both repetition rate and central emission wavelength.

Enhanced energy storage performance of lead-free Sr0.7Bi0.2TiO3 ceramics via tape casting

Abstract The development of pulsed power technology demands high energy storage density dielectric materials. In this study, Sr0.7Bi0.2TiO3 relaxor ferroelectric (rFE) ceramic thick films were prepared using a tape-casting process. The ceramics exhibit a dense structure and typical rFE hysteresis curves, achieving an energy storage density of 4.77 J cm−3 and efficiency of 94.4%, attributed to the high polarization intensity, low remnant polarization, and low hysteresis loss of rFE. Additionally, the material demonstrates good temperature stability. Moreover, the Sr0.7Bi0.2TiO3 ceramic thick films show advantages in charge-discharge performance, capable of discharging within hundreds of nanoseconds and achieving a power density of 137 MW cm−3. Overall, the Sr0.7Bi0.2TiO3 ceramic thick film exhibits a comprehensive performance advantage in terms of energy storage density, efficiency, and power density. Additionally, the material was fabricated using the tape-casting process, which is compatible with subsequent multilayer ceramic capacitor production, indicating potential for further performance enhancement.

Ultrafast Polarization‐Maintaining Fiber Lasers: Design, Fabrication, Performance, and Applications

AbstractUltrafast polarization‐maintaining fiber lasers (UPMFLs), with superior optical performance and high immunity to environmental disturbances, are highly preferable in a variety of industrial and scientific applications such as high‐precision micromachining and biomedical imaging. Especially, the utilization of PM fibers endows the laser intrinsic stability, thereby enabling the construction of robust and low‐noise optical frequency comb systems. To meet more demanding application challenges, continuous efforts have been invested in the design and fabrication of UPMFLs, aiming to reach unprecedented levels of various pulse parameters, that is, to achieve shorter pulse duration, higher or lower repetition rate, and higher pulse energy. This review presents a detailed overview of different passive mode‐locking techniques for pulsed operation and the most significant achievements in UPMFLs. Representative advances at 1.0, 1.55, and 2.0 µm spectral regions are presented and summarized. The state‐of‐the‐art lasing performance is application‐oriented, and conversely, optical improvements in all‐PM pulsed lasers promote emerging applications, which are also discussed and analyzed. How to overcome the bottlenecks of UPMFLs in terms of pulse duration, repetition rate, emission wavelength, and pulse energy to make them powerful tools for physical, medical, and biological applications remains challenging in the future.

Non-linear optics for an online probing of the specific surface area of nanoparticles in the aerosol phase

In the present study the generation of non-linear optical (NLO) effects, such as second harmonic generation (SHG), by black carbon particles, also named soot, and by other types of nanoparticles in aerosol phase is quantified and analysed. Its potential for measuring the specific surface area of an aerosol is put forward. SHG is a Non Linear Optical phenomenon that is typically used in biosciences and fundamental physics and has shown to have large potential for the investigation of surface sensitive phenomena. It exists in two forms, coherent SHG and incoherent SHG, also named Hyper Rayleigh Scattering (HRS). While applications on particles in solution or organic molecules located on the surface of droplets exist, the SHG naturally induced by solid nanoparticles in aerosol phase without any SHG enhancing additive has neither been detected nor quantified yet. The present work aims at narrowing this gap by exposing a jet of well-characterized nanoaerosols to a femtosecond laser featuring high peak pulse energies allowing to induce NLO phenomena. The experiments are carried out in an innovative optical setup allowing to analyse the NLO response resolved in time, wavelength and angle, thus having the capability to isolate SHG from other phenomena, such as laser filamentation. The optical setup was calibrated in order to quantify the generated signal power and optimized in order to have a high sensitivity and in order to avoid NLO generation from its own optical elements. The results confirm that soot particles, as well as DEHS droplets and arc generated carbon nanoparticles, feature SHG at intensities that are more than 7 orders of magnitude smaller than that of static light scattering. SHG depends in particular on aggregate and/or monomer size. On the other hand, SHG induced by soot does not seem to depend on the organic or elementary carbon content. The experiments also show that the detected NLO signal increases linearly with particle surface area, independently of the particle shape or composition. Finally, the angular response of NLO signal is fundamentally different from that of linear scattering. Due to the isotropic nature of the angular response, the observed SHG signal is probably non-coherent and thus related to Hyper Raleigh Scattering. These findings show the potential of non-linear optics, in particular to quantify in situ the specific surface of an aerosol. Giving access to this information which is crucial in the evaluation of toxicity of aerosols, the present work can thus give way to a new class of laser based diagnostics for aerosols.

Development of a fs-pulsed laser pretreatment process on thin-walled nickel to improve adhesion for adhesive bonding applications

Due to its inert surface, producing adhesive bonds on nickel is challenging and requires a surface pretreatment. A laser pretreatment process on nickel is investigated using a Yb:YAG slab laser at 780 fs pulse length. The process is varied in pulse density, pulse energy, and focus position to produce various surface structures on a nanometer scale. The surface structures are categorized topologically in scanning electron microscopy (SEM). Random nanostructures, laser-induced periodic surface structures (LIPSS), and process vapor depositions are observed. To quantify the adhesion properties of the produced surfaces, peel tests are conducted using a two-component epoxy adhesive. All investigated process parameters lead to a significant increase in peel strength; however, high pulse density and high pulse energy in focus lead to the highest peel strengths. These process parameters generally produce LIPSS and process vapor depositions on the surface, which might be linked to the high peel strengths. The analysis of the fracture pattern shows an adhesion failure, and in SEM, a partial failure of adhesive and adherent is visible. The surface structures are fully wetted by the adhesive on a sub-micrometer level. Nanoparticles deposited from the process plasma are broken out of the surface during the peel tests. A general trend to high accumulated fluence for best results in peel strength is shown.

Synthesizing gas-filled anti-resonant hollow-core fiber Raman lines enables access to the molecular fingerprint region

The synthesis of multiple narrow optical spectral lines, precisely and independently tuned across the near- to mid-infrared region, is a pivotal research area that enables selective and real-time detection of trace gas species within complex gas mixtures. However, existing methods for developing such light sources suffer from limited flexibility and very low pulse energy, particularly in the mid-infrared domain. Here, we introduce a concept that is based on the combination of an appropriate design of near-infrared fiber laser pump and cascaded configuration of gas-filled anti-resonant hollow-core fiber technology. This concept enables the synthesis of multiple independently tunable spectral lines, with >1 μJ high pulse energies and a few nanoseconds pulse width in the near- and mid-infrared regions. The number and wavelengths of the generated spectral lines can be dynamically reconfigured. A proof-of-concept laser beam synthesized of two narrow spectral lines at 3.99 µm and 4.25 µm wavelengths is demonstrated and combined with photoacoustic modality for real-time SO2 and CO2 detection. The proposed concept also constitutes a promising way for infrared multispectral microscopic imaging.

An In Vitro Study of 355‐nm Laser Ablation of Atherosclerotic Lesions Model

ABSTRACTA study of 355 nm laser with high pulse energy across various types of atherosclerotic lesion models is presented. The 355 nm laser pulses (10 ns) are delivered via a single fiber (600 μm diameter), and the ablation of calcified tissue, lipid tissue, and thrombus‐like tissue are studied under varied laser fluence (40–70 mJ/mm2) and repetition rate (5–30 Hz). The contact and noncontact ablation processes of chicken tibia samples (calcified tissue) are compared at 60 mJ/mm2 and 30 Hz, and the size of ablation particles is in the range of 0.1–1 μm. At the same repetition rate, the advancement rate of tricalcium phosphate samples reaches 150 μm/s at 70 mJ/mm2. Calcified and lipid models demonstrate predictable increases in ablation with higher laser fluence and repetition rate. The fresh porcine blood clot samples exhibit high‐quality ablation with good channel effect at 50 mJ/mm2 and 30 Hz.

Pulse compressor architecture to enable next-generation high-energy petawatt-class lasers.

The maximum energy obtainable within a single aperture of a high-energy petawatt-class (HEPW) laser is typically limited by the pulse compressor. This work evaluates the potential impact of two new pulse compression grating technologies (HELD gratings and TM polarization) on HEPW laser systems. A compressor architecture is proposed that implements these grating advancements in order to support ∼6× higher pulse energies than currently demonstrated. This increase in energy and intensity could have substantial benefits to high-flux secondary sources and enable new applications.

Optical Energy Increasing in a Synchronized Motif-Ring Array of Autonomous Erbium-Doped Fiber Lasers

This work investigates the enhancement of optical energy in the synchronized dynamics of three erbium-doped fiber lasers (EDFLs) that are diffusively coupled in a unidirectional ring configuration without the need for external pump modulation. Before the system shows stable high-energy pulses, different dynamic behaviors can be observed in the dynamics of the coupled lasers. The evolution of the studied system was analyzed using different techniques for different values of coupling strength. The system shows the well-known dynamic behavior towards chaos at weak coupling, starting with a fixed point at low coupling and passing through Hopf and torus bifurcations as the coupling strength increases. An interesting finding emerged at high coupling strengths, where phase locking occurs between the frequencies of the three lasers of the system. This phase-locking leads to a significant increase in the peak energy of the EDFL pulses, effectively converting the emission into short, high amplitude pulses. With this method, it is possible to significantly increase the peak energy of the laser compared to a continuous EDFL single pulse.