Picosecond laser filament-guided electrical discharges in air at 1 kHz repetition rate.

Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long distances. Here we demonstrate the stable generation of laser filament-guided electrical discharge columns in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of 7 ps duration at repetition rates up to 1 kHz and we discuss the processes leading to breakdown. A current proportional to the laser pulse energy is observed to arise as soon as the laser pulse arrives, initiating a high impedance phase of the discharge. Full breakdown, characterized by impedance collapse, occurs 100 ns to several µs later. A record 4.7-fold reduction in breakdown voltage for dc-biased discharges, which remains practically independent of the repetition rate up to 1 kHz, is observed to be primarily caused by a single laser pulse that produces a large (∼80%) density depression. The radial gaps between the filamentary plasma channel and the hollowed electrodes employed are shown to play a significant role in the breakdown dynamics. A rapid increase of 3-4 orders of magnitude in current is observed to follow the formation of localized radial current channels linking the filament to the electrodes. The increased understanding and control of kHz repetition rate filament-guided discharges can aid their use in applications.

Guided Mode Evolution and Ionization Injection in Meter-Scale Multi-GeV Laser Wakefield Accelerators.

We show that multi-GeV laser wakefield electron accelerators in meter-scale, low density hydrodynamic plasma waveguides operate in a new nonlinear propagation regime dominated by sustained beating of lowest order modes of the ponderomotively modified channel; this occurs whether or not the injected pulse is linearly matched to the guide. For a continuously doped gas jet, this emergent mode beating effect leads to axially modulated enhancement of ionization injection and a multi-GeV energy spectrum of multiple quasimonoenergetic peaks; the same process in a locally doped jet produces single multi-GeV peaks with <10% energy spread. A three-stage model of drive laser pulse evolution and ionization injection characterizes the beating effect and explains our experimental results.

EPIDEMIOLOGY OF DEPRESSIVE STATES IN ACUTE AND CHRONIC CONDITIONS.

Depression is the only silent cause that mainly affects the adult population and manifests itself in this case in 4% of the world population. However, more than three quarters of those affected belong to land in urbanization without receiving any type of treatment; a situation that represents a gap in access to mental health services. Now, the hallucinatory relationships mean that this condition has a high level of competition with chronic diseases such as HIV, diabetes, lung disease, asthma, arthritis, angina pectoris and cerebral palsy; Assimilation, it has been detected that patient with affective disorders such as coronary syndrome, inflammation, malnutrition, pain, stress and even critical stages of COVID-19 infection act as risk factors for the development of the disease. In this context, as a result of concern for public health, particularly in countries following the crisis, this study presents a proposal to carry out a review regarding the prevalence of depression in the presence of aggravated cases and crises. Strategies are implemented to address this situation. For this, a systematic review of the literature was carried out, complemented with bibliometric data on scientific contributions, with a period of 10 years (2011-2021) registered in the databases: Web of Science, Scopus and PubMed. In this way, the results allowed us to identify that, in recent years, in the fight to combat this problem, various remedies were used for its treatment and prevention; in which the focus is on the modification of health behaviors and collaborative care, which seeks quality of life in cases of patients with chronic diseases. On the other hand, the bibliometric information allows us to determine that the United States, Australia and Canada are the countries with the greatest scientific production on the subject. It is concluded that, although health services have demonstrated and improved their strategies in recent years, and that part of them have been supported by technological innovation, there are bridging markets at the cultural and socioeconomic level that the treatment and primary care of these patients.

Ablating Ion Velocity Distributions in Short-Pulse-Heated Solids via X-Ray Doppler Shifts.

Solids ablate under laser irradiation, but experiments have not previously characterized the initiation of this process at ultrarelativistic laser intensities. We present first measurements of bulk ion velocity distributions as ablation begins, captured as a function of depth via Doppler-shifted x-ray line emission from two viewing angles. Bayesian analysis indicates that bulk ions are either nearly stationary or flowing outward at the plasma sound speed. The measurements quantitatively constrain the laser-plasma ablation mechanism, suggesting that a steplike electrostatic potential structure drives solid disassembly.

Homogeneous, Micron-Scale High-Energy-Density Matter Generated by Relativistic Laser-Solid Interactions.

Short-pulse, laser-solid interactions provide a unique platform for studying complex high-energy-density matter. We present the first demonstration of solid-density, micron-scale keV plasmas uniformly heated by a high-contrast, 400 nm wavelength laser at intensities up to 2×10^{21} W/cm^{2}. High-resolution spectral analysis of x-ray emission reveals uniform heating up to 3.0 keV over 1 µm depths. Particle-in-cell simulations indicate the production of a uniformly heated keV plasma to depths of 2 µm. The significant bulk heating and presence of highly ionized ions deep within the target are attributed to the few MeV hot electrons that become trapped and undergo refluxing within the target sheath fields. These conditions enabled the differentiation of atomic physics models of ionization potential depression in high-energy-density environments.

Implementing High Q-Factor HTS Resonators to Enhance Probe Sensitivity in 13C NMR Spectroscopy.

Nuclear magnetic resonance spectroscopy (NMR) probes using thin-film high temperature superconducting (HTS) resonators provide exceptional mass sensitivity in small-sample NMR experiments for natural products chemistry and metabolomics. We report improvements in sensitivity to our 1.5 mm 13C-optimized NMR probe based on HTS resonators. The probe has a sample volume of 35 microliters and operates in a 14.1 T magnet. The probe also features HTS resonators for 1H transmission and detection and the 2H lock. The probe utilizes a 13C resonator design that provides greater efficiency than our previous design. The quality factor of the new resonator in the 14.1 T background field was measured to be 4,300, which is over 3x the value of the previous design. To effectively implement the improved quality factor, we demonstrate the effect of adding a shorted transmission line stub to increase the bandwidth and reduce the rise/fall time of 13C irradiation pulses. Initial NMR measurements verify 13C NMR sensitivity is significantly improved while preserving detection bandwidth. The probe will be used for applications in metabolomics.

Wake dynamics of air filaments generated by high-energy picosecond laser pulses at 1 kHz repetition rate.

We investigated the filamentation in air of 7 ps laser pulses of up to 200 mJ energy from a 1.03 µm-wavelength Yb:YAG laser at repetition rates up to f=1kHz. Interferograms of the wake generated show that while pulses in a train of repetition rate f=0.1kHz encounter a nearly unperturbed environment, at f=1kHz, a channel with an axial air density hole of ∼20% is generated and maintained at all times by the cumulative effect of preceding laser pulses. Measurements at f=1kHz show that the energy deposited decreases proportional to the air channel density depletion, becoming more pronounced as the repetition rate and pulse energy increase. Numerical simulations indicate that contrary to filaments generated by shorter duration pulses, the electron avalanche is the dominant energy loss mechanism during filamentation with 7 ps pulses. The results are of interest for the atmospheric propagation of joule-level picosecond pulses from Yb:YAG lasers, of which average powers now surpass 1 kW, and for channeling other directed energy beams.

Solid-Density Ion Temperature from Redshifted and Double-Peaked Stark Line Shapes.

Heß spectral line shapes are important for diagnosing temperature and density in many dense plasmas. This work presents Heß line shapes measured with high spectral resolution from solid-density plasmas with minimized gradients. The line shapes show hallmark features of Stark broadening, including quantifiable redshifts and double-peaked structure with a significant dip between the peaks; these features are compared to models through a Markov chain Monte Carlo framework. Line shape theory using the dipole approximation can fit the width and peak separation of measured line shapes, but it cannot resolve an ambiguity between electron density n_{e} and ion temperature T_{i}, since both parameters influence the strength of quasistatic ion microfields. Here a line shape model employing a full Coulomb interaction for the electron broadening computes self-consistent line widths and redshifts through the monopole term; redshifts have different dependence on plasma parameters and thus resolve the n_{e}-T_{i} ambiguity. The measured line shapes indicate densities that are 80-100% of solid, identifying a regime of highly ionized but well-tamped plasma. This analysis also provides the first strong evidence that dense ions and electrons are not in thermal equilibrium, despite equilibration times much shorter than the duration of x-ray emission; cooler ions may arise from nonclassical thermalization rates or anomalous energy transport. The experimental platform and diagnostic technique constitute a promising new approach for studying ion-electron equilibration in dense plasmas.

Extreme degree of ionization in homogenous micro-capillary plasma columns heated by ultrafast current pulses.

Homogeneous plasma columns with ionization levels typical of megaampere discharges are created by rapidly heating gas-filled 520-µm-diameter channels with nanosecond rise time current pulses of 40 kA. Current densities of up to 0.3 GA cm^{-2} greatly increase Joule heating with respect to conventional capillary discharge Z pinches, reaching unprecedented degrees of ionization for a high-Z plasma column heated by a current pulse of remarkably low amplitude. Dense xenon plasmas are ionized to Xe^{28+}, while xenon impurities in hydrogen discharges reach Xe^{30+}. The unique characteristics of these hot, ∼300:1 length-to-diameter aspect ratio plasmas allow the observation of unexpected spectroscopic phenomena. Axial spectra show the unusual dominance of the intercombination line over the resonance line of He-like Al by nearly an order of magnitude, caused by differences in opacities in the axial and radial directions. These plasma columns could enable the development of sub-10-nm x-ray lasers.

Comparison of two different laser wavelengths' dental bleaching results by photo-Fenton reaction: in vitro study.

The purpose of this study was to perform a preliminary in vitro test on the possible use of two different laser wavelengths, 405 and 532 nm, to improve the dental bleaching results. To perform the test, the degradation of a dye, rhodamine B, under the effects of hydrogen peroxide was used. One hundred and twenty vials were divided into four groups of 30 samples each and, while three of them were irradiated with different wavelengths, 365 nm (reference), 405 nm and 532 nm, the fourth was the non-irradiated control group. Each of the four groups was further divided into three subgroups of 10 cuvettes (n = 10) each. The three subgroups included a group with a rhodamine (RH) solution, a rhodamine and hydrogen peroxide (RH + HP) solution and a rhodamine plus hydrogen peroxide and ferrous gluconate (RH + FR) solution. When hydrogen peroxide was present, only UVA irradiation was able to produce significant results, whereas when the photo-Fenton reaction occurred, all the three wavelengths were able to produce a significant degradation of rhodamine B, with better results for longer wavelengths in comparison with short wavelengths. Within the limitations of this in vitro study, the light of the two laser devices, even remaining less effective than UV activation, showed its ability to improve the performance of bleaching agents based on Fenton photocatalysis, whereas when used in combination with hydrogen peroxide only, the 405-nm laser displayed a small effect and the 532-nm laser produced no effects.

KTP and Er:YAG laser dental bleaching comparison: a spectrophotometric, thermal and morphologic analysis.

The aim of this study was to compare the results, in terms of temperature, colour change and morphology, of two different laser wavelengths with two different concentrations of hydrogen peroxide (HP). The lasers used were KTP (potassium-titanyl-phosphate) laser (λ = 532 nm (PD = 1.98 W/cm2)) and Er:YAG laser (λ = 2940 nm (PD = 2.54 W/cm2)). The bleaching gels used were PolaOffice 35% HP gel and PolaOffice+ 6% HP gel (SDI, Australia). Thirty-six extracted human teeth were selected and divided into two groups. For the 35% HP treatment, 18 teeth were randomly assigned to three subgroups: (1) HP gel without laser irradiation vs. HP gel + KTP laser irradiation; (2) HP gel without laser irradiation vs. HP gel + Er:YAG irradiation; and (3) HP gel + KTP laser irradiation vs. HP gel + Er:YAG irradiation. The same protocol was used for the 6% HP bleaching treatment. The bleaching results were analysed by a spectrophotometer, the thermal elevation by K thermocouples and the enamel surface by a scanning electron microscope (SEM). The Kruskal-Wallis test and the Mann-Whitney test were performed, and the data were analysed using the software StatView and the free Web statistics tool BiostaTGV. The thermal elevation of the Er:YAG groups was higher than KTP, while only the group 35% HP gel vs. 35% HP gel + Er:YAG showed significant colour differences (p < 0.05). SEM photographs showed slight enamel surface morphologic alterations after bleaching treatment. The Er:YAG laser may improve the bleaching results of 35% HP even if it increases the gel temperature, when compared to the KTP laser.

Point defects in Sc2O3 thin films by ion beam sputtering.

We show that the concentration of oxygen interstitials trapped in Sc2O3 films by ion beam sputtering from metal targets can be controlled by modifying deposition conditions. We have identified point defects in the form of oxygen interstitials that are present in Sc2O3 films, in significantly high concentrations, i.e., ∼10(18) cm(-3). These results show a correlation between the increase of oxygen interstitials and the increase in stress and optical absorption in the films. Sc2O3 films with the lowest stress and optical absorption loss at 1 µm wavelength were obtained when using a low oxygen partial pressure and low beam voltage.

Er:YAG laser for brackets bonding: a SEM study after debonding.

BACKGROUND: The introduction of Er:YAG laser in dentistry for ablation of hard tissues advocated an alternative method of enamel etching for orthodontics purpose. MATERIALS AND METHODS: 55 extracted human third molars were inserted in acrylic resin blocks and divided into five groups of 11 teeth. Group 1 was treated with 37% orthophosphoric acid for 30 seconds. Group 2 was treated with laser irradiation (Er:YAG Fidelius III, Fotona, Slovenia) at 80 mJ and 4 Hz. Group 3 underwent laser treatment (80 mJ, 4 Hz), followed by 37% orthophosphoric acid for 30 seconds. The teeth in Group 4 were treated with laser at 40 mJ and 10 Hz. The teeth in Group 5 were treated with laser (40 mJ, 10 Hz), followed by 37% orthophosphoric acid for 30 seconds. The adhesive remnant index was determined after debonding. RESULTS: Kruskas-Wallis test showed that location parameters (median and mean) are significantly different between Groups 2 and 4 when compared with control group; on the contrary no significant difference was detected between Groups 3 and 5 with the controls. CONCLUSION: The use of Er:YAG laser alone, as in Groups 2 and 4, showed no significant advantages over phosphoric acid in the bonding procedure for orthodontics brackets.

Multichannel Doppler fiber-imager spectrometer for spatiotemporal characterization of high-intensity laser-driven plasmas.

We demonstrate a flexible multichannel fiber-based imaging Doppler spectrometer to characterize plasmas in high intensity (≥1 × 1018 W/cm2) laser-plasma experiments at high repetition rates. This instrument collects data from ×21 different plasma locations combining optical fibers and a single imaging spectrometer. This diagnostic maps the plasma velocity evolution as a function of time with sub-pico-second resolution. Experimental results showing 2D velocity measurements of plasma with 20 µm spatial resolution are presented. Intensities of the order of 1018 W/cm2 were used to generate a plasma, while a much less intense, frequency doubled (400 nm), probe beam (1011 W/cm2) was used to measure the Doppler shift from the plasma critical surface. The instrument can be scaled to a larger number of channels (e.g., 100) still using a single spectrometer.

In-situ relative calibration of Bragg crystals with Monte Carlo line ratio analysis.

X-ray line emission spectra can thoroughly characterize hot plasmas, especially when line shapes and ratios convey distinct aspects of plasma conditions. However, the high spectral resolution required for observing line shapes is often at odds with the large bandwidth required to observe many line ratios across a wide spectral range. One strategy to obtain high spectral resolution over a wide bandwidth is to use multiple crystals with calibrated reflectivity so that line intensities across different crystals can be compared. Here, we explore the use of a low-resolution, wide-bandwidth mica survey spectrometer to infer relative reflectivity of two high-resolution, narrow-bandwidth quartz crystals. A Monte Carlo error analysis determines comparable x-ray line ratios measured from both spectrometers, resulting in an in situ calibration factor and associated uncertainty for the relative reflectivity of the high-resolution crystals.

High repetition-rate dual-channel X-ray spectrometer for high-intensity laser-plasma experiments.

We describe the development and demonstration of a high-repetition-rate-capable dual-channel (DC) x-ray spectrometer designed for high-intensity laser-plasma experiments (≥1×1021 W/cm2). The spectrometer, which operates at high repetition rates, is limited only by the refresh rate of targets and the camera's frame rate. It features two channels, each equipped with a flat highly oriented pyrolytic graphite (HOPG) crystal and a unique detector plane, allowing it to resolve two distinct x-ray bands: approximately 7-10 and 10-13 keV. Each detector plate carrier holds two slots for active (scintillators) or passive (imaging plates) x-ray detectors. We present the design and testing of the HR-DC-HOPG using both the COMET laser (10 J, 0.5 ps shot/4 min) at LLNL's Jupiter Laser Facility and the SCARLET laser (10 J, 30 fs shot/min) at Ohio State University. The results demonstrate the spectrometer's performance across various laser energies, target materials, pulse shapes, and detector types.

Single-shot soft x-ray laser linewidth measurement using a grating interferometer.

The linewidth of a 14.7 nm wavelength Ni-like Pd soft x-ray laser was measured in a single shot using a soft x-ray diffraction grating interferometer. The instrument uses the time delay introduced by the gratings across the beam to measure the temporal coherence. The spectral linewidth of the 4d1S0-4p1P1 Ni-like Pd lasing line was measured to be Δλ/λ=3×10(-5) from the Fourier transform of the fringe visibility. This single shot linewidth measurement technique provides a rapid and accurate way to determine the temporal coherence of soft x-ray lasers that can contribute to the development of femtosecond plasma-based soft x-ray lasers.

Compact high repetition rate Thomson parabola ion spectrometer.

We present the development of a compact Thomson parabola ion spectrometer capable of characterizing the energy spectra of various ion species of multi-MeV ion beams from >1020W/cm2 laser produced plasmas at rates commensurate with the highest available from any of the current and near-future PW-class laser facilities. This diagnostic makes use of a polyvinyl toluene based fast plastic scintillator (EJ-260), and the emitted light is collected using an optical imaging system coupled to a thermoelectrically cooled scientific complementary metal-oxide-semiconductor camera. This offers a robust solution for data acquisition at a high repetition rate, while avoiding the added complications and nonlinearities of micro-channel plate based systems. Different ion energy ranges can be probed using a modular magnet setup, a variable electric field, and a varying drift-distance. We have demonstrated operation and data collection with this system at up to 0.2 Hz from plasmas created by irradiating a solid target, limited only by the targeting system. With the appropriate software, on-the-fly ion spectral analysis will be possible, enabling real-time experimental control at multi-Hz repetition rates.

Variable magnetic field electron spectrometer to measure hot electrons in the range of 50-460 keV.

Resonance absorption (RA) occurs when a p-polarized electromagnetic wave, obliquely incident on an inhomogeneous plasma, tunnels past its turning point and resonantly excites an electron plasma wave (EPW) at the critical density. This phenomenon is important, for instance, in the direct drive approach to inertial fusion energy and is a particular example of a wider phenomenon in plasma physics known as mode conversion, which is crucial for heating magnetic fusion devices, such as tokamaks, via RF heating. Direct measurement of these RA-generated EPW accelerated hot electrons, with energy in the range of a few tens to a few hundreds of keV, is a challenging task due to the relatively low deflecting magnetic fields needed. The solution described here is a magnetic electron spectrometer (MES) with a continually changing magnetic field, lower at the entrance of the MES and gradually increasing toward the end, that enables the measurement of a wide spectral range of electrons with energies between 50 and 460 keV. Electron spectra taken in a LaserNetUS RA experiment were acquired from plasmas generated by irradiating polymer targets with the combination of an ∼300 ps pulse followed by a series of ten high intensity 50-200 fs duration laser pulses from the ALEPH laser at Colorado State University. The high intensity beam is designed as spike trains of uneven duration and delay pulses in order to modify the RA phenomenon.

Differentiating multi-MeV, multi-ion spectra with CR-39 solid-state nuclear track detectors.

The development of high intensity petawatt lasers has created new possibilities for ion acceleration and nuclear fusion using solid targets. In such laser-matter interaction, multiple ion species are accelerated with broad spectra up to hundreds of MeV. To measure ion yields and for species identification, CR-39 solid-state nuclear track detectors are frequently used. However, these detectors are limited in their applicability for multi-ion spectra differentiation as standard image recognition algorithms can lead to a misinterpretation of data, there is no unique relation between track diameter and particle energy, and there are overlapping pit diameter relationships for multiple particle species. In this report, we address these issues by first developing an algorithm to overcome user bias during image processing. Second, we use calibration of the detector response for protons, carbon and helium ions (alpha particles) from 0.1 to above 10 MeV and measurements of statistical energy loss fluctuations in a forward-fitting procedure utilizing multiple, differently filtered CR-39, altogether enabling high-sensitivity, multi-species particle spectroscopy. To validate this capability, we show that inferred CR-39 spectra match Thomson parabola ion spectrometer data from the same experiment. Filtered CR-39 spectrometers were used to detect, within a background of ~ 2 × 1011 sr-1 J-1 protons and carbons, (1.3 ± 0.7) × 108 sr-1 J-1 alpha particles from laser-driven proton-boron fusion reactions.