Laser Pulse Duration Research Articles

Envelope effect of Rydberg States Generation in Strong Laser Pulses

Rydberg atoms are important building blocks for quantum technologies, exploited to new applications in quantum computing, quantum communication and quantum sensing due to their unique tunable quantum properties.Besides the widely-used few-photon resonant excitation for the specific Rydberg state, multiple Rydberg states can be populated coherently and effciently through the frustrated tunneling ionization or the Coulomb potential recapture effect in strong laser field. The Rydberg states excitation in strong field provides an opportunity to realize the ultrafast quantum control on Rydberg atom and bridge the strong field physics and quantum information technology. <br>Using the Classical Trajectory Monte Carlo method and Qprop package to solve Time-Dependent increases with the parameter of the asymmetric laser envelope. Based on the Quantitative Rescattering theory, the calculated time-dependence of recapture rate is negatively related to the laser envelope and the residual laser interaction time, which is termed as envelope effect. Combined with the carrier-wave effect, an analytic formula is proposed to calculate the Rydberg states population:$Y(t) \propto W_0(t) \frac{t-\tau+c}{f(t)} \cos (\omega t+\phi)$ This results open the door to enhance the Rydberg states generation using the laser envelope control, benefiting the future quantum technology based on the Rydberg states generated in the strong laser field.(a) Laser electric fields with the same pulse duration τ = 10T<sub>0</sub> and different asymmetric parameters α. Black solid line, red dashed line and blue dashed-dotted line are for α = -0.6, 0, 0.6 respectively. (b) The yields of Rydberg states change with the asymmetric parameter under different laser pulse duration. Black solid line, red dashed line and blue dashed-dotted line are for τ = 1010T<sub>0</sub>, 1510T<sub>0</sub>, 2010T<sub>0</sub> respectively. Schrödinger Equation, we calculate the population of Rydberg states. Our results show that the population.

RF Characterisation of Laser Treated Copper Surfaces for the Mitigation of Electron Cloud in Accelerators

In accelerator beam chambers and RF waveguides, electron cloud and multipacting can be mitigated effectively by reducing the secondary electron yield (SEY). In recent years, it has been established that laser-engineered surface structuring is a very efficient method to create a copper surface with a SEY maximum close to or even below unity. Different laser pulse durations, from nanoseconds to picoseconds, can be used to change surface morphology. Conversely, the characteristics that minimise the SEY, such as the moderately deep grooves and the redeposited nanoparticles, might have unfavourable consequences, including increased RF surface resistance. In this study, we describe the techniques used to measure the surface resistance of laser-treated copper samples using an enhanced dielectric resonator with 12 cm diameter sample sizes operating in the GHz range. The quantification basis lies in a non-contact measurement of the high-frequency losses, focusing on understanding the variation of surface resistance levels depending on the specifics of the treatment and possible post-treatment cleaning procedures.

Unraveling photodissociation dynamics by sub-femtosecond ultraviolet pulses: insights into fragmental kinetics and carrier-envelope phase characterization

The duration of laser pulses and the carrier-envelope phase (CEP) play a crucial role in shaping kinetic energy release (KER) spectra. In this study, we performed theoretical calculations on pulse duration-dependent KER spectra, ranging from hundreds to sub-femtoseconds, focusing on the MgH+ scenario. Our findings reveal a distinct shift in KER peaks from sub-cycle pulses, deviating from the resonance energy. Utilizing two-level perturbation theory, we identify that this shift is attributable to the energy-dependent transition matrix elements. Moreover, our investigation uncovers a notable CEP effect in KER from sub-cycle pulses, arising from interference between counter-rotating and rotating terms within a single ultraviolet photon transition. To leverage this insight, we propose a novel pump-probe methodology for precise CEP characterization of ultra-short laser pulses. We hope this method would promise advancements in understanding and manipulating ultrafast processes.

Treatment of plasma coatings by laser remelting

The article analyzes the effect of reflow and thermal cycling by laser beam on the structure and properties of plasma eutectic coatings. The facts of carbon diffusion into the solid phase at a distance of 150-200 microns with a laser pulse duration of 4 ms have been established. This is due to the high deformation rates that occur in the zone of thermal influence under pulsed laser action. This effect is aimed at increasing both the surface and volumetric strength of the sprayed coatings.

Characteristics of laser-induced plasma generated in water and in air with different nanosecond laser pulse durations

The characteristics of laser-induced plasma generated in water and in air were compared with two laser pulse durations of 6 ns and 17 ns.

An investigation on the laser welding process parameter effects on the failure mode of tailor welded blanks during the formability testing

The ability to produce high-quality weld with the least distortion and heat affected zone width by the Nd:YAG laser welding process has made it one of the best candidates for steel tailor welded blanks (TWBs). The effect of process parameters including laser peak power, pulse duration, welding speed, and thickness ratio on the mechanical properties and failure modes of TWBs were investigated. TWBs was made of St12 carbon steel sheets with different thickness of 0.5 mm, 1 mm, and 1.5 mm. The weld zone hardness profile in all samples followed a similar pattern, in that the maximum hardness was in the weld metal and gradually fell throughout the heat affected zone (HAZ) until it reached the hardness of the base metal at the end of the HAZ and the hardness of weld metal increased as the average joint thickness increased. Based on the distribution of hardness in different regions of the weld zone a simple model was proposed for failure mode. Weld metal failure mode (WFM) happened as a result of weld metal thickness reduction caused by incomplete weld penetration or excessive penetration. The heat input per unit volume of weld in thin sheet (Hin) was defined as a criterion that determines failure mode. Therefore, a qualitative criterion was proposed for the prediction of failure mode. Based on this simple model, there is an appropriate limit for Hin for all thickness ratios at which the failure mode is base metal failure mode (BFM). The WMF happens at values lower and higher than this appropriate value range. The experiments approved that BFM and the highest formability and joint strength were obtained when 11J/mm3<Hin<37J/mm3.

Performance of brushite plaster as kidney stone phantoms for laser lithotripsy.

Artificial phantoms used in photothermal near-infrared laser lithotripsy research generally fail to mimic both the chemical and the physical properties of human stones. Though high-energy, 1J pulses are capable of fracturing hard human stones into several large fragments along natural boundaries, similar behavior has not been observed in commonly used gypsum plasters like BegoStone. We developed a new brushite-based plaster formulation composed of ≈90% brushite that undergoes rapid fracture in the manner of human stones under fragmentation pulse regimes. Single-pulse (1J) ablation crater volumes for phantoms were not significantly different from those of pure brushite stones. Control over crater volumes was demonstrated by varying phosphorous acid concentration in the plaster formulation. Fragmentation of cylindrical brushite phantoms was filmed using a high-speed camera which demonstrated rapid fragmentation in < 100µs during the bubble expansion phase of a short pulse from a high-powered Ho:YAG laser (Lumenis Pulse 120H). The rapid nature of observed fracture suggests increasing laser pulse energy by increasing laser pulse duration will not improve fragmentation performance of laser lithotripters. Brushite plaster phantoms are a superior alternative to gypsum plasters for laser lithotripsy research due to their better mimicry of stone composition, controllable single-pulse crater volumes, and fragmentation behavior.

Ultra-fast laser pulses as a probe of electron dynamics: A next generation QTAIM perspective

We investigate the construction of an ultra-fast laser probe to determine the response of the electron dynamics of ethane using next generation QTAIM (NG-QTAIM). This is undertaken by applying a pair of simulated left and right circularly polarized ultra-fast laser pulses of duration 10 fs. A proportional increase in the C-C BCP bond strain with peak electric field was discovered. NG-QTAIM was used to identify a characteristic morphology associated with ultra-fast laser probes. Candidate ultra-fast laser probes were selected on the basis of the ground state population remaining undisturbed at a time t = 15 fs.

Production of 13.5 nm light with 5% conversion efficiency from 2 μ m laser-driven tin microdroplet plasma

We demonstrate the efficient generation of extreme ultraviolet (EUV) light from laser-produced plasma (LPP) driven by 2 μm wavelength laser light as an alternative for 10 μm CO2 gas LPP currently employed in EUV lithography machines for high-volume manufacturing of semiconductor devices. High conversion efficiencies of laser light into “in-band” EUV photons up to 5.0% are achieved by homogeneously heating the plasma that is laser-generated from preshaped tin microdroplet targets. Scaling the laser pulse duration, spot size, and intensity yields a high in-band EUV energy output of up to 12.5 mJ. The EUV emission source size is studied under a similar parameter range and is shown to match typical etendues of EUV optic columns. Our findings make 2 μm LPP a particularly promising candidate to power future EUV nanolithography.

Primary and Secondary Processes in the Ultraviolet Photodissociation of CpCo(CO)2 (Cyclopentadienylcobalt Dicarbonyl).

We investigated the photodissociation dynamics of CpCo(CO)2 (cyclopentadienylcobalt dicarbonyl) in metal-to-ligand charge transfer (MLCT) bands. By employing DFT calculations, the absorption band (210-240 nm) was characterized as a charge transfer from the Co center to the Cp (cyclopentadienyl, C5H5) ligand. Ion imaging was utilized to analyze the CO fragments and coordinatively unsaturated complexes (CpCoCO, CpCo, and CoC3H3) across the entire MLCT band. Measuring the production yields of individual unsaturated complexes as a function of photolysis wavelength by considering wavelength dependence indicated the involvement of several photochemical pathways: the first photodissociation and sequential dissociation of CpCo(CO)2, and the second photodissociation of unsaturated intermediates within the pulse duration of the photolysis laser. The recoil velocity shifts of CpCo and CoC3H3 were attributed to the onset of the sequential dissociation of CpCoCO. Evidence for the second photodissociation of CpCoCO was obtained through the matching of linear momenta between the CO(v = 0, 1) and CpCo fragments. The DFT calculations performed to determine the electronic structures and potential energy curves for photoinduced CO loss in CpCo(CO)2 and CpCoCO supported our interpretation of the experimental results. This study presents a practical approach to selectively detecting specific processes among the mixture of products and intermediates when photolyzing transition-metal carbonyls, as their concurrent generation is unavoidable in laser-based experiments.

Optimized selection of neodymium laser parameters for successful enlarged veins treatment.

Full clearance and no side effects method of treating enlarged veins was successfully accomplished by one laser session. This is the ambition and dream of both dermatologists and patients. Most vascularity treatment protocols had shown some unpleasant adverse effects. The purpose of the present work is to work out, in advance, the accurate dose of laser pulse duration and fluence in order to treat varicose veins in the face, arms and legs with no adverse effects. This mission required the calculation of the exact rise in temperature of the enlarged vein; prior to laser treatment. These pre-calculated temperature rise values were tested on 20 subjects in order to have the best clinical outcomes; using fundamental frequency (1064nm) pulsed Nd: YAG laser. This work necessitated the use of pulse length (15-30ms), spot size (3, 5mm), fluence (110-190J/cm2) and skin cooling temperature (3-18°C). Cooling of the skin before and after the treatment was needed to guarantee ultimate impactful results without side effects.

Lasers for the treatment of eyebrow microblading and cosmetic tattoo pigment: a review of the literature.

We aim to discuss the use of laser for the treatment of eyebrow microblading and cosmetic tattoo complications through a review of the literature. Our research question is whether quality-switched or picosecond laser is superior for the removal of eyebrow tattoos. This structured review was conducted using a PubMed search using the search terms "laser tattoo removal" AND "cosmetic tattoo" AND "eyebrow" with the article type filtered to "case reports," "clinical trial," and "randomized controlled trial" ranging from dates 1994-2023. All case reports or series evaluating the effect of laser on eyebrow cosmetic tattooing pigment were included. We summarize the results of 11 studies evaluating the use of laser for cosmetic tattoo removal, with 129 patients treated specifically for eyebrow pigment. Most studies (8/11) report Fitzpatrick skin type or race. Seven studies utilize quality-switched (QS) neodymium-doped yttrium aluminum garnet (Nd:YAG), alexandrite or ruby, three used picosecond (PS) Nd:YAG or alexandrite, and three used carbon dioxide (CO2) laser. We report laser energy, spot size, and pulse duration, as well as treatment outcomes and adverse events. Historically, methods of pigment removal included dermabrasion, cryosurgery, electrosurgery, radiofrequency, infrared light, intense pulsed light, and surgical excision; however, these methods often led to poor cosmetic outcomes including scarring and further dyspigmentation. QS laser treatments provided superior cosmetic outcomes and thus were considered the gold standard treatment option for pigment removal. However, the advent of PS lasers has challenged this given their increased selectivity, lower fluence requirements, and reduction in surrounding thermal damage. Our review demonstrates that PS Nd:YAG is quicker and more effective that QS Nd:YAG in the treatment of eyebrow tattoos. Additionally, the paradoxical darkening seen with QS lasers is less common with PS lasers. We also demonstrate that CO2 laser may be a helpful adjunct to QS or PS laser. This review focuses on Fitzpatrick skin type and race, providing a unique perspective on the use of laser treatment in skin of color, which often poses an additional treatment challenge.

Ultrafast ultraviolet laser-induced voltage of air

In this work, the time-scale laser-induced voltage (LIV) of air was investigated under KrF excimer laser irradiation. The LIV response was fitted by a sum of three exponential functions, where the fitted parameters were influenced by the bias voltage Vb and the laser energy Ein. Higher Vb produced significant LIV. An exponential relationship was observed between the Ein and LIV signal amplitude (Vp). After decreasing the adjustable resistor, the LIV trace was almost triangular and symmetrical due to the impedance effect with the response time which was completely limited by the laser pulse duration. As a potential application, the LIV of air presented a viable method for single-pulse laser detection.

Transient responses of dielectrics during ultrashort pulsed laser irradiation using a generalized thermoelastic model considering temperature-dependent thermophysical properties

A novel model involving electron dynamics, electron-lattice interactions, and thermoelastic excitation for dielectrics exposed to ultrashort pulsed laser is proposed. The thermoelastic equations are modified based on the G-L generalized thermoelasticity and consider the temperature-dependent thermophysical properties. An axisymmetric problem of ultrashort pulsed laser irradiation on fused silica is presented. The fully-coupled equations are solved simultaneously using the finite element method to obtain the transient electron density, electron temperature, lattice temperature, and stresses. The evolution of transient responses and the effects of laser intensity, pulse duration, and temperature-dependent thermophysical properties are analyzed in detail. It was found that there are kinks in the distribution of transient responses, which is attributed to the rapid change of reflectivity. The axial stress has wave-like characteristics. The electron temperature is slightly lower than the lattice temperature after the thermal equilibrium is achieved. Maybe the temperature-dependence of lattice thermal conductivity could be neglected to reduce computational expenses.

Minimum separation between two pump pulses for ultrafast double magnetization switching in GdFeCo

Femtosecond laser ultrafast thermally induced magnetization switching (TIMS) has also attracted much attention due to its ability to trigger a single switching at the picosecond timescale. Current studies have shown that after a TIMS excited by a laser pulse, excitation of the switch again via TIMS does not require equilibrium between the subsystems. In this work, the main investigation is on the various possible cases of magnetization dynamics in GdFeCo under two short-delayed pulse excitations, as well as the factors limiting the minimum separation for double TIMS. These conditions are relevant for the potential application of TIMS to memory devices as it affects both the speed limit at which rewritten data is available and demonstrates the importance of spatial confinement of a laser pulse to bit size. The results show that low energy and short pulse duration lasers are prerequisites for double TIMS in GdFeCo based on simulations of atomic spin dynamics. By changing the damping constants of the alloy, we can shorten the minimum pulse separation between two pump pulses for double TIMS to 2 ps to approach terahertz frequency of write/erase cycles.

Enhancement of cell attachment on Ti6Al4V via surface modifications using pulsed laser surface melting

The surface topography of biomedical implants made of Ti6Al4V significantly impacts cell attachment. This work aims to modify the surface topography of the Ti6Al4V surface using pulse laser surface melting (pLSM) to enhance fibroblast cell attachment. In pLSM, short laser pulses irradiate the surface resulting in localised melting and creating new features upon resolidification. Thus, surfaces are modified without the addition or removal of material. The effect of laser pulse duration and hatch spacing on the attachment of NIH3T3 fibroblast cells is examined in this study. The cells were cultured on the pLSM-textured surfaces and two control surfaces, viz., as-received and manually polished, and the results were studied after 24 h of cell culture using fluorescence microscopy. pLSM-textured surfaces showed improved cell attachment compared to the control surfaces. The surface textured with a 10 μs pulse duration and 75 % hatch spacing showed 395 % and 91 % improvement in attached cell density compared to the as-received surface and manually polished surface, respectively, because the induced feature size was comparable to the size of NIH3T3 fibroblast cells. Additionally, the periodic textures developed by pLSM resulted in a homogenous distribution of the cells across the area.

Ultrafast pulse duration measurement method of near-infrared pulses for a broad range of wavelengths using two-photon absorption in a liquid and fluorescent dye solution.

A novel characterization method to measure the pulse duration of ultrafast near-IR pulses is introduced, which uses simple tabletop optics, is relatively inexpensive, and is expected to work in a broad wavelength range. Our diagnostic tool quantitatively characterizes the laser pulse duration of any near-IR wavelength assuming a Gaussian pulse shape with a linear chirp. We negatively prechirp near-IR pulses with a home-built broadband pulse compressor (BPC) and send this prechirped beam through a cell filled with a low-molar solution of a fluorescent dye in a liquid. After two-photon absorption, this dye fluoresces in the visible, and we record this visible signal as a function of the propagation distance in the liquid cell. We calibrate the group velocity dispersion (GVD) of our home-built BPC device against the known GVD of the compressor of our 800nm laser and confirm this value using geometric considerations. Now knowing the GVD of BPC and the recorded visible signal for various amounts of negative chirp, let us extract the smallest pulse duration of the near-IR pulse from this visible signal. As a useful corollary, our analysis also enables the direct measurement of the GVD for liquids and the indirect measurement of the absorption coefficient for liquids in the near-IR range, in contrast to indirect GVD measurements that rely on methods such as the double derivative of the refractive index.

High-harmonic generation in liquids with few-cycle pulses: effect of laser-pulse duration on the cut-off energy.

High-harmonic generation (HHG) in liquids is opening new opportunities for attosecond light sources and attosecond time-resolved studies of dynamics in the liquid phase. In gas-phase HHG, few-cycle pulses are routinely used to create isolated attosecond pulses and to extend the cut-off energy. Here, we study the properties of HHG in liquids, including heavy water, ethanol and isopropanol, by continuously tuning the pulse duration of a mid-infrared driver from the multi- to the two-cycle regime. Similar to the gas phase, we observe the transition from discrete odd-order harmonics to continuous extreme-ultraviolet emission. However, the cut-off energy is shown to be entirely independent of the pulse duration. These observations are confirmed by ab-initio simulations of HHG in large liquid clusters. Our results support the notion that the cut-off energy is a fundamental property of the liquid, independent of the driving-pulse properties. Our work implies that few-cycle mid-infrared laser pulses are suitable drivers for generating isolated attosecond pulses from liquids and confirm the capability of high-harmonic spectroscopy to determine the mean-free paths of slow electrons in liquids.

All-optical switching based on coherent control of metasurface

In this paper, we propose a novel method to design ultrafast all-optical switchings based on the coherent perfect absorption principle of metasurface. Using the coherent interaction between two beams of coherent light and the metasurface, the absorption can be modulated between 0.3% and 98. 3%. Since no nonlinear dielectric is used, the ultrafast all-optical switching function can be achieved at arbitrary low intensity conditions. We further studied the mechanism of resonant absorption on metasurface, and analyzed the influence of geometric parameters on resonant absorption. Through time-domain simulation analysis, when the incident laser pulse duration is 40 fs, the switching response time is 82 fs, which provides a switching contrast ratio of more than 108.

A 90° retro-reflecting mirror based autocorrelator for temporal duration and pulse front tilt measurements of ultra-short laser pulse

A 90° retro-reflecting mirror based autocorrelator for temporal duration and pulse front tilt measurements of ultra-short laser pulse