Pulses In Air Research Articles

Filamenting-ring-Airy-beam femtosecond pulse in air at 10 m through quasi-Gaussian beam modulation with a dedicated phase plate

Filamenting-ring-Airy-beam femtosecond pulse in air at 10 m through quasi-Gaussian beam modulation with a dedicated phase plate

Dynamics of a Discharge Initiated by a Powerful Femtosecond Laser Pulse in Atmospheric Pressure Air in Pre-Breakdown Electrical Fields

Numerical modeling of the dynamics of a discharge initiated by a high-power femtosecond laser pulse in air at atmospheric pressure in pre-breakdown fields was carried out. Calculations were conducted within the framework of a 1D-axisymmetric model that describes the evolution of the radial profiles of the main parameters of the discharge under study. The model includes a system of reaction that determine gas heating and a detailed description of the kinetic processes in a given discharge, as well as a system of gas-dynamic equations to describe the expansions of the heated channel. The results of calculations of the breakdown time of the discharge gap are conсistent with the measurement data over the entire studied range of electric field strengths, E = 9–17 kV/cm. It is shown that one of the key factors determining the evolution of the parameters of a given discharge is the rate of gas heating.

THz Generation by Two-Color Plasma: Time Shaping and Ultra-Broadband Polarimetry.

The generation of terahertz radiation via laser-induced plasma from two-color femtosecond pulses in air has been extensively studied due to its broad emission spectrum and significant pulse energy. However, precise control over the temporal properties of these ultra-broadband terahertz pulses, as well as the measurement of their polarization state, remain challenging. In this study, we review our latest findings on these topics and present additional results not previously reported in our earlier works. First, we investigate the impact of chirping on the fundamental wave and the effect of manipulating the phase difference between the fundamental wave and the second-harmonic wave on the properties of generated terahertz pulses. We demonstrate that we can tune the time shape of terahertz pulses, causing them to reverse polarity or become bipolar by carefully selecting the correct combination of chirp and phase. Additionally, we introduce a novel technique for polarization characterization, termed terahertz unipolar polarimetry, which utilizes a weak probe beam and avoids the systematic errors associated with traditional methods. This technique is effective for detecting polarization-structured terahertz beams and the longitudinal component of focused terahertz beams. Our findings contribute to the improved control and characterization of terahertz radiation, enhancing its application in fields such as nonlinear optics, spectroscopy, and microscopy.

Turbulence-enhanced THz generation by multiple chaotically-distributed femtosecond filaments in air

Remote generation of electromagnetic waves in the terahertz (THz) by the volume of air medium gains increasing scientific interest due to the demand for this spectral range in solving various practical problems including those belonging to the nonlinear atmospheric optics. During self-focusing and filamentation of high-power femtosecond laser pulses in air, the source of THz radiation is the plasma of laser filaments. One of the main challenges of THz generation by a laser filament is increasing the value of optical energy conversion to the long-wavelength band. In this paper, we present the results of our studies on DC-biased THz generation during single-color filamentation in air of focused femtosecond Ti:Sapphire-laser pulses (800 nm, pulse energy up to 40 mJ). The distinctive feature of our study is that a femtosecond optical pulse propagates through a spatially-localized heated air layer containing randomly inhomogeneous refractive index perturbations, which mimics strong air turbulence. For the first time to our knowledge, we show, that the turbulent air layer formed at the beginning of the optical path allows increasing the yield of THz radiation up to 1.5 times due to the formation of multiple chaotically-arranged filaments resulting from random perturbations of the optical beam energy profile that reduces the subsequent THz (re)absorption in the filament plasma.

Surface-Enhanced Raman Spectroscopy of Ammonium Nitrate Using Al Structures, Fabricated by Laser Processing of AlN Ceramic.

This work presents results on laser-induced surface structuring of AlN ceramic and its application in Surface-Enhanced Raman Spectroscopy (SERS). The laser processing is performed by nanosecond pulses in air and vacuum. Depending on the processing conditions, different surface morphology can be obtained. The ablation process is realized by ceramic decomposition as the formation of an aluminium layer is detected. The efficiency of the fabricated structures as active substrates in SERS is estimated by the ability of the detection of ammonium nitrate (NH4NO3). It is conducted for Raman spectrometer systems that operate at wavelengths of 514 and 785 nm where the most common commercial systems work. The obtained structures contribute to enhancement of the Raman signal at both wavelengths, as the efficiency is higher for excitation at 514 nm. The limit of detection (LOD) of ammonium nitrate is estimated to be below the maximum allowed value in drinking water. The analysis of the obtained results was based on the calculations of the near field enhancement at different conditions based on Finite Difference Time Domain simulation and the extinction spectra calculations based on Generalized Mie scattering theory. The structures considered in these simulations were taken from the SEM images of the real samples. The oxidation issue of the ablated surface was studied by X-ray photoelectron spectroscopy. The presented results indicated that laser structuring of AlN ceramics is a way for fabrication of Al structures with specific near-field properties that can be used for the detection of substances with high social impact.

Using double pulse laser ablation in air to enhance the strength of laser-driven shocks

In the process of multi-pulse laser ablation, inter-pulse delay time, Δt, is known to be an important parameter for maximizing ablation efficiency as well as impulse imparted to the target. In this work, using photon Doppler velocimetry, we show that for single pairs of colinear pulses (1064 nm, 8 ns, ∼ 60 J cm-2 per pulse) in air, the peak free surface velocity of the back surface of an aluminum target (125 µm thick) is increased, by a factor of nearly 3, when Δt = 10 microseconds, compared with both pulses arriving simultaneously (Δt = 0). Fast imaging of the ablation process suggests this enhancement is due to rarefaction of the contiguous air in the passage of the leading shock produced by ablation, which then in turn allows a larger fraction of the energy of the second pulse to reach the target surface. This interpretation is strengthened by additional experiments in which the two pulses do not overlap on the target surface, but the shock strength is nevertheless enhanced. Given a fixed energy budget this work suggests a prescription for maximizing laser-driven shock strength by judicious choice of inter-pulse delay.

Polarization change of femtosecond laser pulses in air measured by electric-field-induced second-harmonic generation.

We experimentally demonstrated the polarization change of femtosecond laser pulses in air by using electric-field-induced second-harmonic generation (E-FISHG) for the first time to our knowledge. The polarization change from linear to elliptical was observed at the laser intensity over the filamentation threshold. These results suggest that the polarization change can occur by the birefringence caused by filamentation. This phenomenon can be used for new applications such as an ultra-fast and precise three-dimensional electric field measurement by E-FISHG. In addition, E-FISHG can be an excellent tool to investigate the characteristics of femtosecond laser propagation such as filamentation.

Dynamics of an Electrical Discharge Initiated by a Powerful Femtosecond Laser Pulse in Atmospheric Pressure Air in Pre-Breakdown Fields

Dynamics of an Electrical Discharge Initiated by a Powerful Femtosecond Laser Pulse in Atmospheric Pressure Air in Pre-Breakdown Fields

Evolutions of streamer dynamics and discharge instabilities under repetitive pulses in humid air

The presence of water molecules in air introduces complexities to residual charge transports and energy relaxations that may provoke streamer discharge instabilities under repetitive pulses. Evolutions of pulse-periodic positive streamer dynamics were investigated in humid air. Pulse-sequence and temporally resolved diagnostics were implemented to capture discharge evolutions. The streamer development and evolutions of charged species in humid air are qualitatively analyzed based on a 2D–0D combined simulation. Evolution features of streamer behaviors in humid air include the faster filamentation of the primary streamer, pronounced propagation selectivity to previous secondary streamers, more branches of both primary and secondary streamers, and accelerated secondary streamer into stagnation. The repetitively pulsed breakdown is proceeded by the progressive axial prolongation of secondary streamers with bright heads and faint tails. Nonintuitively, the withstanding capability does not illustrate dramatic differences in dry air and humid air especially at high pulse repetition frequency. High-density residing hydrated ions with high electron bound energies (impeding streamer propagation) and the enhanced thermal release to cause higher reduced electric field (facilitating streamer propagation) may contrarily affect evolutions and discharge instability developments of positive streamer in humid air.

Light-guiding-light-based temporal integration of broadband terahertz pulses in air

The next generation of all-optical computation platforms prefers the light-guiding-light (LGL) scheme inside a medium that envisions circuitry-free and rapidly reconfigurable systems powered by dynamic interactions between light beams. Currently, suitable LGL materials and corresponding mechanisms are in urgent need. In this work, we proposed ubiquitous air as a restorable LGL signal manipulation medium with transient air-plasma waveguide circuits. Briefly, by focusing femtosecond laser beams in free space, the created atmospheric plasma filament array via photoionization was able to guide terahertz (THz) pulses along its epsilon-near-zero zone with a 1/f-profile spectral response. Consequently, this achieved a time-domain integration of the THz pulse in broad bandwidth. When the pumping laser was sequentially turned off and on, this air-plasma multi-filament structure was erased and rebuilt within nano- and femto-seconds, respectively, allowing rapid and repeated rearrangements of the all-optical stage. Furthermore, this air-based LGL information processing approach is promising to pave the way toward all-optical calculations during free-space directional transmission of THz waves, in which way the delivered THz signal can be remotely controlled.

Self-compression of femtosecond laser pulses in ambient air through conical radiation.

We demonstrate self-compression of 98 fs near-infrared laser pulses down to 8.8 fs in ambient air, utilizing self-phase modulation in air and negative dispersion in the properties of a laser-induced plasma. The blueshifted pulses achieve self-compression through conical radiation, eliminating the need for additional dispersion compensation. The results highlight a simple and compact approach to generate sub-10 fs laser pulses without additional measures for time-resolved applications in ultrafast diagnostics and spectroscopy.

Multimodal E-Textile Enabled by One-Step Maskless Patterning of Femtosecond-Laser-Induced Graphene on Nonwoven, Knit, and Woven Textiles.

Personal wearable devices are considered important in advanced healthcare, military, and sports applications. Among them, e-textiles are the best candidates because of their intrinsic conformability without any additional device installation. However, e-textile manufacturing to date has a high process complexity and low design flexibility. Here, we report the direct laser writing of e-textiles by converting raw Kevlar textiles to electrically conductive laser-induced graphene (LIG) via femtosecond laser pulses in ambient air. The resulting LIG has high electrical conductivity and chemical reliability with a low sheet resistance of 2.86 Ω/□. Wearable multimodal e-textile sensors and supercapacitors are realized on different types of Kevlar textiles, including nonwoven, knit, and woven structures, by considering their structural textile characteristics. The nonwoven textile exhibits high mechanical stability, making it suitable for applications in temperature sensors and micro-supercapacitors. On the other hand, the knit textile possesses inherent spring-like stretchability, enabling its use in the fabrication of strain sensors for human motion detection. Additionally, the woven textile offers special sensitive pressure-sensing networks between the warp and weft parts, making it suitable for the fabrication of bending sensors used in detecting human voices. This direct laser synthesis of arbitrarily patterned LIGs from various textile structures could result in the facile realization of wearable electronic sensors and energy storage.

Formation mechanisms of silicon surface structuring using single-multiple nanosecond laser pulses in ambient air and cold plasma

The formation mechanisms of the surface structures of silicon using single-multiple nanosecond laser pulses at the focus, and below the focus in ambient air and cold plasma was investigated for ablation at 2–5 J cm−2. Ablation in cold plasma, excited by a dielectric-barrier-discharge source in flowing air by applying sinusoidal voltage of 3–5 kV/30 kHz led to regular and consistent low-spatial-frequency and high-spatial-frequency grating-type structures. For plasma, structures were formed inside the crater and suggest that plasma hindered effective coupling of the laser energy to the surface, which resulted in a controlled ablation. Contrary to the ablation in plasma, for ambient air, due to excessive ablation, overlapped-ripples were formed outside the ablation crater. For the increased laser shots fired below the focus, the surface pattern spatially expands and sustains a far-range order. The localized interrupted and broken features were also observed due to the incubation effect of statically fired laser shots. This study finds that ablation in clod plasma seems a promising new concept to use for shaping and structuring surfaces of industry-accepted materials for electronic and photonic devices, such as solar-cells, detectors, large-area grating, and optical waveguides.

GaAs ablation with ultrashort laser pulses in ambient air and water environments

Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment.

Manipulation of femtosecond laser filamentation by wire mesh amplitude mask

The results of numerical simulation on the propagation of high-power femtosecond laser pulses in air under conditions of the amplitude modulation are presented. Laser pulse amplitude modulation is realized by using the metal mesh-masks, which divide the initial laser beam into lower-energy parts (subbeams). We show that, in general, the beam energy partitioning by metal meshes reduces the total length of beam filamentation region in air, whereas the longitudinal continuity of the laser plasma distribution in the filaments is considerably improved. A strong dependence of the filamentation region parameters (starting coordinate, length, longitudinal continuity) on the position of the mesh-mask relative to the laser beam axis is also revealed. It turns out that under certain conditions, when the beam axis points to the mesh crossing, the spatial position of the filaments can be shifted further along the propagation path by increasing the size of the mesh cells. Alternatively, if the beam center exposes the mesh cell opening, the filamentation start coordinate decreases monotonically when the mesh becomes sparser. Additionally, the parameters of the filamentation region exhibit high sensitivity to the mesh wire thickness that can dominate the influence of mesh position and cell size.

Influence of Humidity and Salinity on the Discharge Characteristics of a Short Rod-Plane Gap Under Negative DC Voltage

In this article, the effects of air humidity and salinity on the discharge characteristics of a short rod-plane gap under negative dc voltage are investigated experimentally. The discharge of the rod-plane gap was recorded using a measuring resistance, photomultiplier tube, and ultraviolet imager. The experimental results show that corona discharge of rod electrode can be observed in the rod-plane gap when the relative humidity is lower than 70%, and furthermore, partial discharge of water molecules in the air can also be observed in the rod-plane gap when the relative humidity is higher than 70%. The partial discharge inception voltage (PDIV) decreases with the increase of air humidity and salinity, and the corona discharge inception voltage (CDIV) increases slightly with the increase of humidity. The average discharge current increases with the increase of applied voltage and humidity. The repetition rate of the optical pulse and the Trichel pulse increases with the increase of applied voltage. The discharge repetition rate of water molecules in the air can be estimated from the repetition rate difference between the optical pulse and the Trichel pulse. The amplitude of the Trichel pulse in clean air is higher than that in the salty air, while the repetition rate of the Trichel pulse in clean air is lower than that in the salty air, which is due to the charging of NaCl particles during discharge.

MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY

You have accessJournal of UrologyCME1 Apr 2023MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY Yuri Pishchalnikov, William Behnke-Parks, and Marshall Stoller Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003269.10AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ureteroscopic lithotripsy breaks urinary stones using laser pulses delivered to the stone via optical fibers. Degradation of fibers reduces the efficacy of lithotripsy and varies with fiber diameter, stone composition, laser pulse energy and duration. The goal of this work was to reveal the physical mechanisms of fiber-tip damage (burnback) in water and air. METHODS: The dynamics of fiber-tip damage was studied using a high-speed camera Shimadzu HPV-X2 at a frame rate up to two million frames per second. The camera was mounted to a microscope focused on the 242-µm glass-core-diameter fiber positioned in direct contact with a target—typically, a glass slide coated with a 25±5 µm layer of hydroxyapatite (Himed, NY). Selected experiments were conducted with BegoStones and whole surgically retrieved urinary stones. Damaged fibers were cleaved to start each series of 20 pulses with flat fiber tips. Laser pulses were produced using a Lumenis VersaPulse holmium:YAG laser. Temporal profiles of infrared laser pulses and flashes of visible light were resolved using photodetectors. Cross-sectional profiles of laser-beam energy were assessed using Zap-It paper. Microscope images were used to measure the burnback length of the fiber. RESULTS: Burnback of optical fibers was associated with flashes of light (sparks) observed both in water and in air. Sparks in air could crack and fragment the fiber during single laser pulse. Twenty pulses in air produced the burnback length of 0.37 mm at 1.0 J (95% CI: 0.11–0.64 mm) and 0.14 mm at 0.6 J (95% CI: 0.10–0.18 mm), smaller than that at 1.0 J (p=0.010). In water, the fibers were damaged by sparks during the laser pulse and after the pulse during the collapse of laser-induced cavitation bubbles. Contribution of cavitation varied from insignificant to most dramatic, breaking a 1.1-mm length of the fiber in a single laser pulse. Cavitation without sparks showed no burnback with only minor damage of cladding (500 pulses, 1.0 J). Sparks were associated with an increased absorption of laser energy and were observed at laser energies typically >0.5 J and only with certain target materials near the fiber tip. Cross-sections of laser beams were larger with fibers damaged in air than that in water (p=0.007) and both were larger than that with undamaged fibers (p<0.005). CONCLUSIONS: These results suggest that the burnback degradation of optical fibers is associated mainly with laser-induced heating, ionization, and optical breakdown of target material. A better understanding of the mechanisms of fiber-tip damage will aid in development of future improvements to minimize degradation of optical fibers. Source of Funding: Research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R43DK129104. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e473 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...

Simulation of nonlinear propagation of femtosecond laser pulses in air for quantitative prediction of the ablation crater shape.

The utilization of sub-100 fs pulses has attracted attention as an approach to further improve the quality and precision of femtosecond laser microfabrication. However, when using such lasers at pulse energies typical for laser processing, nonlinear propagation effects in air are known to distort the beam's temporal and spatial intensity profile. Due to this distortion, it has been difficult to quantitatively predict the final processed crater shape of materials ablated by such lasers. In this study, we developed a method to quantitatively predict the ablation crater shape, utilizing nonlinear propagation simulations. Investigations revealed that the ablation crater diameters derived by our method were in excellent quantitative agreement with experimental results for several metals over a two-orders-of-magnitude range in the pulse energy. We also found a good quantitative correlation between the simulated central fluence and the ablation depth. Such methods should improve the controllability of laser processing with sub-100 fs pulses and contribute to furthering their practical application to processes over a wide pulse-energy range, including conditions with nonlinear-propagating pulses.

A computational study on the energy efficiency of species production by single-pulse streamers in air

We study the energy efficiency of species production by streamer discharges with a single voltage pulse in atmospheric dry air, using a 2D axisymmetric fluid model. Sixty different positive streamers are simulated by varying the electrode geometry, the pulse duration and the applied voltage. Between these cases, the streamer radius and velocity vary by about an order of magnitude, but the variation in the maximal electric field is significantly smaller, about 30%. We find that G-values for the production of N(4S), O(3P), NO and N2O, which have relatively high activation energies, vary by about 30% to 60%. This variation is mainly caused by two factors: differences in the fraction of energy deposited in the streamer head region, and differences in the maximal electric field at the streamer head. When accounting for both factors, our computed G-values are in good agreement with an analytic estimate proposed by Naidis (2012 Plasma Sources Sci. Technol. 21 042001). We also simulate negative streamers and find that their production of N(4S), O(3P) and NO is less energy efficient. The results suggest that energy efficiency can be increased by reducing Joule heating in the streamer channel and by increasing the maximal electric field at the streamer head, for example by using short voltage pulses with a high applied voltage.

Formation of picosecond laser-induced periodic surface structures on steel for knee arthroplasty prosthetics

The formation of laser-induced periodic surface structures (LIPSS) on mirror-polished 304-grade stainless steel sheets with dimensions 25 mm × 25 mm × 0.8 mm upon irradiation with picosecond laser pulses in air and water environments at different wavelengths, number of pulses, and laser energy densities was investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the LIPSS. Tunable periodicity of the LIPSS was observed in both media at different wavelengths and fluence. Fluence was shown to be the main formation parameter of LIPSS; however, the medium was also demonstrated to play an important role. Our results show that LIPSS can be successfully generated on stainless steel in a single-step process and that they can be easily modified by adjusting laser parameters.