High-power Ultrashort Laser Research Articles

Study of burst mode for enhancing the ps-laser cutting performance of lithium-ion battery electrodes

The demand for lithium-ion batteries (LIBs) has increased significantly, leading to an increased focus on high quality production methods. In response to this growing demand, laser technology has been increasingly used for electrode notching and cutting. In addition, the advent of high-power ultrashort lasers equipped with burst mode capabilities represents a promising option for electrode cutting of LIBs. On the other hand, these types of lasers for this purpose are relatively unexplored in the literature. This study investigates the effect of various parameters, including the number of pulses per burst (ranging from 1 to 8), the pulse repetition rate (200.0, 550.3, and 901.0 kHz), and the burst shape (equal pulse peak and increasing pulse peak), on the laser cutting process of aluminum foil, cathode, copper foil, and anode. The results indicate that increasing the number of pulses per burst and the pulse repetition rate improves productivity and quality for all materials, with a more significant effect observed for metal foil than for cathode and anode materials due to the different laser-material interactions for metal foil and active material. The burst shape with equal pulse peaks was found to be a more suitable temporal distribution for cutting all materials compared to an increasing pulse peak distribution. The ablation efficiency was evaluated as a function of the peak fluence of a single pulse within the burst. The results emphasize that higher productivity at higher average power can be achieved by increasing the pulse repetition rate toward the MHz range with moderate pulse energies.

Existence of positive solutions for generalized quasilinear Schrödinger equations with Sobolev critical growth

In this paper, we are devoted to establishing that the existence of positive solutions for a class of generalized quasilinear elliptic equations in R N with Sobolev critical growth, which have appeared from plasma physics, as well as high-power ultrashort laser in matter. To begin, by changing the variable, quasilinear equations are transformed into semilinear equations. The positive solutions to semilinear equations are then presented using the Mountain Pass Theorem for locally Lipschitz functionals and the Concentration-Compactness Principle. Finally, an inverse translation reveals the presence of positive solutions to the original quasilinear equations.

Multiplicity results for generalized quasilinear critical Schrödinger equations in RN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb {R}}^N$$\\end{document}

Multiplicity results are proved for solutions both with positive and negative energy, as well as nonexistence results, of a generalized quasilinear Schrödinger potential free equation in the entire RN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb {R}}^N$$\\end{document} involving a nonlinearity which combines a power-type term at a critical level with a subcritical term, both with weights. The equation has been derived from models of several physical phenomena such as superfluid film in plasma physics as well as the self-channelling of a high-power ultra-short laser in matter. Proof techniques, also in the symmetric setting, are based on variational tools, including concentration compactness principles, to overcome lack of compactness, and the use of a change of variable in order to deal with a well defined functional.

The impact of saturable absorber recovery time on hybrid mode-locked fiber lasers with near zero net dispersion

The hybrid mode-locking scheme holds great potential in obtaining high power ultrashort laser source since it overcomes low damage threshold, self-starting difficulty in single real saturable absorber (SA) or artificial SA mode-locking scheme. Here we numerically studied the effect of SA’s recovery time on the stability of laser output in an all polarization-maintaining (PM) Erbium-doped fiber laser with hybrid mode-locking scheme, operating at the near zero net dispersion. The mapping relationship between fiber fused angles of nonlinear polarization rotation (NPR) section and different mode-locking states is demonstrated. The proportion of stable single pulse operating points increased from 7 % to more than 77 %, as the recovery time of the SA was reduced from 10 ps to 0.1 ps. The results indicate that the laser output states with hybrid mode-locking scheme could be highly affected by the SA recovery time, when the cavity net dispersion is in near zero regime.

Sub-two-cycle gigawatt-peak-power LWIR OPA for ultrafast nonlinear spectroscopy of condensed state materials.

The application of high-power, few-cycle, long-wave infrared (LWIR, 8-20 µm) pulses in strong-field physics is largely unexplored due to the lack of suitable sources. However, the generation of intense pulses with >6 µm wavelength range is becoming increasingly feasible with the recent advances in high-power ultrashort lasers in the middle-infrared range that can serve as a pump for optical parametric amplifiers (OPA). Here we experimentally demonstrate the feasibility of this approach by building an OPA pumped at 2.4 µm that generates 93 µJ pulses at 9.5 µm, 1 kHz repetition rate with sub-two-cycle pulse duration, 1.6 GW peak power, and excellent beam quality. The results open a wide range of applications in attosecond physics (especially for studies of condensed phase samples), remote sensing, and biophotonics.

Ultrashort Laser Texturing of Superelastic NiTi: Effect of Laser Power and Scanning Speed on Surface Morphology, Composition and Wettability

Among metallic biomaterials, near-equiatomic NiTi is one of the most promising intermetallic system applicable for biomedical applications, thanks to its high biocompatibility and unique superelasticity (or pseudoelasticity), offering a complete recoverable strain up to 8%. In the prospective uses for bio-devices, the surface processing of NiTi medical components plays a fundamental role for guaranteeing both a Ti oxide passivizing layer for avoiding Ni ion release into the human body and surface morphology for controlling the cell proliferation. Mechanical polishing, thermal, chemical or electro-chemical treatments are typically performed for surface modifications. Recently, laser texturing has been successfully applied for different materials, included NiTi shape memory alloys, and also for tuning the surface properties, such as wettability. In the present work, ultrashort laser surface modification was carried out, through the use of a femtosecond laser, for the surface texturing of commercial superelastic NiTi plates. The main goal is to investigate the correlation among morphology, chemical composition and wettability with the principal process parameters, such as average power and scanning velocity in high power ultrashort laser texturing. Laser patterned surfaces were characterized by means of scanning electron microscopy, 3D-profilometry, XPS analysis and wetting measurements. After the laser treatments, both surface morphology and Ni/Ti ratio were largely modified from the initial surface, depending on the adopted process parameters. The wettability of the laser textured surfaces can be also varied with respect to the initial surface, due to the roughness values and grooves induced by the laser beam scans. The laser texturing process induced a combination between micro and nano structures, depending on the input energy. In details, the surfaces were tuned to lower roughness values (from 0.4 μm to 0.3 μm) with a laser power of 1 W, while it was increased up to 0.65 μm with a laser power of 13 W. The laser surface modification promoted a change of the contact angle from 70° of the untreated condition up to 135° to the surface laser treated with a power of 13 W.

Simulation study of quasi-monoenergetic high-energy proton beam based on multiple laser beams driving

High-energy proton beams have extensive and important applications. Traditional proton accelerators are bulky and costly. The high-power laser pulse technology provides a new proton acceleration scheme based on the interaction between laser and plasma, and has the advantage of miniaturization. Furthermore, comparing with traditional proton accelerators, the proton acceleration gradient by high-power laser pulses can be increased by three orders of magnitude. The proton beams with high brightness, narrow pulse width, and good directionality can be generated in theory within a very small effective size, and they are suitable for fields such as nuclear physics and particle physics, ion beam fast ignition, medical treatment, and proton beam detection. In order to realize laser proton acceleration, a great many of researches of different target configurations and acceleration mechanisms have been reported on proton acceleration driven by ultrashort and high-power lasers. However, owing to the limitation of laser intensity, the energy of proton beam driven by a single-beam laser is difficult to improve to meet the needs of medical applications. In this paper, a new method of driving proton acceleration by multiple ultrashort high-power lasers with grazing incidence on both sides of the microstrip target is proposed. A proton beam with an energy divergence of about 3% and energy of about 165 MeV can be obtained by using the two-beam driving setting. The results of two-dimensional particle-in-cell simulation show that a large number of collimated high-energy electron charges are extracted from both sides of the solid target by laser and injected into the back of the target. A longitudinal bunching field is established on the back of the target, which drives protons to accelerate and bunch to form a quasi-monoenergetic high-energy proton beam. The research also shows that the proton beam with an energy divergence of about 2% and energy of about 250 MeV can be obtained by using four grazing ultrashort high-power lasers on both sides of the microstrip target. The mechanism of multi-laser beams driving proton acceleration provides a new idea for the energy enhancement of the proton beam, and the quasi-monoenergetic high-energy proton beam is expected to be applied to the field of medical treatment.

UV-Femtosecond-Laser Structuring of Cyclic Olefin Copolymer.

We report on the laser ablation of cyclic olefin copolymer using an amplified ultrashort pulsed laser in the ultraviolet spectral range. In addition to a high ablation depth per laser-structured layer up to 74 m at a fluence of 22 J cm, an excellent mean roughness of laser-patterned surfaces down to 0.5 m is demonstrated. Furthermore, with increasing fluence, increasing ablation efficiencies up to mm3 W−1 min−1 are determined. Regarding the quality of the ablation, we observed steep ablation flanks and low debris formation, though for fluences above 10.5 J cm the formation of troughs was observed, being attributed to multiple reflections on the ablation flanks. For comparison, laser ablation was performed under identical conditions with an infrared laser wavelength. The results highlight that UV ablation exhibits significant advantages in terms of ablation efficiency, surface roughness and quality. Moreover, our results show that a larger UV focus spot accelerates the ablation process with comparable quality, paving the way for high-power UV ultrashort pulsed lasers towards an efficient and qualitative tool for the laser machining of cyclic olefin copolymer. The production of complex microfluidics further underlines the suitability of this type of laser.

Existence and nonexistence of entire large solutions to a class of generalized quasilinear Schrödinger equations

This paper is concerned to the class of generalized quasilinear Schrödinger equations which have appeared from plasma physics, as well as high-power ultrashort laser in matter. By introducing a variable replacement and using some iterative methods, the existence and nonexistence of entire large solutions are studied.

On the effect of stimulated raman scattering on THz radiation in the laser plasma interactions

In present study, two-dimensional Particle-In-Cell (PIC) simulations are used to investigate the interaction of ultrashort high-power laser pulses with an under-dense plasma medium. The results of the numerical simulations are followed by some mathematical procedures to obtain the terahertz electric field and the growth rates of the Stimulated Raman Forward (RFS) and Backward Scattering (RBS). The influences of incident laser pulse intensity and initial plasma density are examined on RFS and RBS instabilities and their consequent effects on the characteristics of THz radiation generation. It is seen that at the lower initial plasma densities i.e. 0.0001nc, the larger laser intensities will lead to more broadband and intense THz signals. Where nc=1.74 × 1027m−3 is known as critical plasma density corresponding to the laser pulse frequency. On the other hand, at the higher plasma densities, i.e., 0.0026nc, due to the instabilities growth, the effects of higher laser pulse intensities on the THz emission are insignificant. While for all the considered plasma densities and incident laser intensities, RBS inevitably affects the THz generation, RFS starts to grow for the initial plasma densities of n0=0.0026nc at the incident laser intensities higher than 1 × 1015Wcm−2. Hence, a higher bound is established on the pump intensity which is based on the RFS growth initiation. Thus, to achieve a stable THz signal for the initial plasma density of n0=0.0026nc (4.5 × 1018 cm−3), the incident laser intensity needs to be less than 1 × 1016Wcm−2.

Semiclassical solutions of generalized quasilinear Schrödinger equations with competing potentials

In this paper, we study the generalized quasilinear Schrödinger equations with multiple competing potentials and critical growth, which have appeared from plasma physics as well as high-power ultrashort laser in matter where , , is a even function, , for all , as for some constants and for all . Under suitable assumptions on the potentials , and , we obtain the existence and concentration of positive solutions and prove that the semiclassical solutions with maximum points concentrating at the special set or characterized by , and . Furthermore, for any sequence or , converges in to a ground state solution v of

Survey of spatio-temporal couplings throughout high-power ultrashort lasers.

The investigation of spatio-temporal couplings (STCs) of broadband light beams is becoming a key topic for the optimization as well as applications of ultrashort laser systems. This calls for accurate measurements of STCs. Yet, it is only recently that such complete spatio-temporal or spatio-spectral characterization has become possible, and it has so far mostly been implemented at the output of the laser systems, where experiments take place. In this survey, we present for the first time STC measurements at different stages of a collection of high-power ultrashort laser systems, all based on the chirped-pulse amplification (CPA) technique, but with very different output characteristics. This measurement campaign reveals spatio-temporal effects with various sources, and motivates the expanded use of STC characterization throughout CPA laser chains, as well as in a wider range of types of ultrafast laser systems. In this way knowledge will be gained not only about potential defects, but also about the fundamental dynamics and operating regimes of advanced ultrashort laser systems.

Positive Solutions for a Class of Quasilinear Schrödinger Equations with Nonlocal Term

This paper is considered the existence of positive solutions for a class of generalized quasilinear Schrödinger equations with nonlocal term in RN which have appeared from plasma physics, as well as high-power ultrashort laser in matter. We use a charge of variables and obtain the existence of solutions via minimization argument.

Air-Lasing: High-Resolution Spectroscopy for Atmospheric Remote Sensing

Air-lasing is a cavityless coherent radiation generated in free space from air constituents as the gain medium, featuring significant advantages such as high collimation, high coherence and high intensity. Benefited from the long-range filamentation of high-power ultrashort laser pulses propagating in air, the air-laser can be induced remotely which provides an ideal light source for atmospheric remote sensing and chemical specie-resolved detection. Thanks to the coherent atomic/molecular excitation process accompanying the generation of air laser, remote sensing based on air-laser has high spectral resolution and high detection sensitivity, which is recently proved to be a powerful tool for important applications such as trace molecule detection, greenhouse gas monitoring and industrial pollutant detection. In this short review, the physical mechanism of air laser is briefly introduced, and various applications of air laser remote sensing are reviewed emphatically, and the future research is prospected.

Air-lasing high-resolution spectroscopy for atmospheric remote sensing

Air-lasing is a cavityless coherent radiation generated in free space from air constituents as gain medium, featuring high collimation, high coherence, and high intensity. Benefited from the long-range filamentation of high-power ultrashort laser pulses propagating in air, the air-lasing can be induced remotely, providing an ideal light source for atmospheric remote sensing and chemical species-resolved detection. Owing to the coherent atomic/molecular excitation process accompanied with the generation of air laser, remote sensing based on air-lasing has high spectral resolution and high detection sensitivity, which recently proved to be a powerful tool for important applications such as in trace molecule detection, greenhouse gas monitoring and industrial pollutant detection. In this short review, the physical mechanism of air lasing is briefly introduced, and various applications of air laser remote sensing are reviewed emphatically, and the future research is prospected.

Phototoxicity induced in living HeLa cells by focused femtosecond laser pulses: a data-driven approach.

Nonlinear optical microscopy is a powerful label-free imaging technology, providing biochemical and structural information in living cells and tissues. A possible drawback is photodamage induced by high-power ultrashort laser pulses. Here we present an experimental study on thousands of HeLa cells, to characterize the damage induced by focused femtosecond near-infrared laser pulses as a function of laser power, scanning speed and exposure time, in both wide-field and point-scanning illumination configurations. Our data-driven approach offers an interpretation of the underlying damage mechanisms and provides a predictive model that estimates its probability and extension and a safety limit for the working conditions in nonlinear optical microscopy. In particular, we demonstrate that cells can withstand high temperatures for a short amount of time, while they die if exposed for longer times to mild temperatures. It is thus better to illuminate the samples with high irradiances: thanks to the nonlinear imaging mechanism, much stronger signals will be generated, enabling fast imaging and thus avoiding sample photodamage.

Passively mode-locked fiber laser based on graphene covered single-mode fiber with inner short waveguides

A saturable absorber based on graphene film covered single-mode fiber with inner short waveguides is proposed and demonstrated for passively mode-locked laser operation. The output laser pulses produced have the center wavelength of 1556.9 nm and pulse width of 830.5 fs at the fundamental repetition rate of 18.7 MHz. Such a saturable absorber is highly robust as the graphene film is covered on the surface of single-mode fiber, instead on tapered fiber or side-polished fiber. Moreover, compared with the saturable absorber based on clamping the graphene film between the two fiber connectors in a fiber adaptor, our device provides a large interaction surface area, thus effectively avoiding the thermal damage and ensuring a long time and stable system operation. The device is attractive for high power ultra-short laser pulse generation.

Dynamics of femtosecond synthesized coronary profile laser beam filamentation in air

Multiple filamentation in air of high-power ultrashort laser radiation with a transverse intensity profile resembling a corona composed of several annularly distributed independent top-hat sub-beams is theoretically studied. Through the numerical solution of the time-averaged nonlinear Schrödinger equation, we study the spatio-angular dynamics of a near-infrared annular combined beam (CB) along the optical path by varying the number and power of the beamlets (corona-spikes). The evident advances in the use of CB in the multiple-filamentation region manipulation and for achieving long-range filamentation are theoretically revealed. In particular, by adjusting the number and aperture of the constituting sub-beams, it makes it possible to significantly delay the CB filamentation onset distance and increase the filamentation length in air. In addition, at the post-filamentation stage of femtosecond pulse propagation under certain conditions, the CBs exhibit significantly lower angular divergence of their most intense part (post-filamentation light channel) compared to the beams with regular unimodal intensity profiles (Gaussian or plateau-like) that provide enhancement of laser power delivered to the receiver over the atmospheric links.

High-speed temporal and spatial beam-shaping combining active and passive elements.

Temporal and spatial shaping of laser beams is common in laser micromachining applications to improve quality and throughput. However, dynamic beam shaping (DBS) of ultrashort, high-power pulses at rates of hundreds of kHz has been challenging. Achieving this allows for full synchronization of the beam shape with high repetition rates, high-power lasers with zero delay time. Such speeds must manipulate the beam shape at a rate that matches the nanosecond to microsecond process dynamics present in laser ablation. In this work, we present a novel design capable of alternating spatial and temporal beam shapes at repetition rates up to 330 kHz for conventional spatial profiles and temporal shaping at nanosecond timescales. Our method utilizes a unique multi-aperture diffractive optical element combined with two acousto-optical deflectors. These high damage threshold elements allow the proposed method to be easily adapted for high power ultrashort lasers at various wavelengths. Moreover, due to the combination of the elements mentioned, no realignment or mechanical movements are required, allowing for high consistency of quality for high throughput applications.

Generation of IR radiation in the interaction of an ultrashort laser pulse with a gas jet

We consider the generation of IR radiation during the interaction of a high-power ultrashort laser pulse with a gas jet using numerical simulation by the particle-in-cell method. The laser pulse parameters correspond to the capabilities of the PEARL sub-petawatt laser facility in Nizhny Novgorod (Russia) when using the compression after compressor approach (CafCA). It is demonstrated that about 1 % of the energy can be converted into radiation in the wavelength range of 5 – 10 μm.