Laser Pulse Parameters Research Articles

Towards single-charge heavy ion beams driven by an ultra-intense laser

The acceleration of super-heavy ions from an ultra-thin lead target irradiated by a femtosecond laser pulse with an intensity in the range of ∼1022–1023 W cm−2 was investigated using an advanced 2D3V particle-in-cell code. It is shown that by properly selecting the laser pulse parameters, it is possible to produce a practically single-charge Pb ion beam with multi-GeV ion energies and the laser-to-ions energy conversion efficiency approaching 30%. At the laser intensity of 1023 W cm−2, Pb ions with the charge state Z = 72 carry over 90% of the total energy of all ions, while the peak intensity and peak fluence of the Pb+72 ion beam are at least two orders of magnitude higher than for other types of ions. In addition, the Pb+72 ion beam is more compact and has a smaller angular divergence than those for other types of ions. The above properties of the Pb+72 ion beam mean that further energy-efficient purification of the beam from other types of ions is possible, even in simple ion transport and selection systems.

Achieving high molecular alignment and orientation for CH_3F through manipulation of rotational states with varying optical and THz laser pulse parameters

Increasing interest in the fields of high-harmonics generation, laser-induced chemical reactions, and molecular imaging of gaseous targets demands high molecular “alignment” and “orientation” (A&O). In this work, we examine the critical role of different pulse parameters on the field-free A&O dynamics of the CH_3F molecule, and identify experimentally feasible optical and THz range laser parameters that ensure maximal A&O for such molecules. Herein, apart from rotational temperature, we investigate effects of varying pulse parameters such as, pulse duration, intensity, frequency, and carrier envelop phase (CEP). By analyzing the interplay between laser pulse parameters and the resulting rotational population distribution, the origin of specific A&O dynamics was addressed. We could identify two qualitatively different A&O behaviors and revealed their connection with the pulse parameters and the population of excited rotational states. We report here the highest alignment of langle {mathrm{cos}^2theta }rangle = 0.843 and orientation of langle {mathrm{cos}(theta )}rangle = 0.886 for CH_3F molecule at 2 K using a single pulse. Our study should be useful to understand different aspects of laser-induced unidirectional rotation in heteronuclear molecules, and in understanding routes to tune/enhance A&O in laboratory conditions for advanced applications.

Large amplitude vibration of a cantilever actuated by a high-frequency pulsed laser.

Laser excitation based on the thermoelastic principle is effective for micro-scale actuation, enabled energy conversion from optical to mechanical. The major advantages lie in non-contact actuation, easy miniaturization, and integration. To avoid surface damage, the laser power per unit is limited, leading to several micrometers of the vibration. In this study, a pure nickel millimeter-sized cantilever is successfully actuated at a low-frequency resonance (around Hz) via a nanosecond pulsed laser. By modal interaction, the energy is transferred from a low-intensity, high-frequency (around kHz) excitation to a low-frequency response with millimeter amplitude. The stable low-frequency resonance of the cantilever was maintained by changing the laser pulse parameters and the illumination locations. We also present a method to control the vibration of the cantilever using a modulated wave (MW: the laser wave modulated by a rectangular wave). The cantilever's amplitude can be efficiently adjusted by changing the laser power or duty cycle of the MW. The resonance frequency of the cantilever also can be altered by optimizing the geometries to meet various actuation requirements. This study enables large actuation (up to tens of millimeters) by laser excitation, facilitating applications in precision manipulation, microfluidic mixing, lab-on-a-chip device, and other related micro actuation devices.

Manipulation of the high-order harmonic generation in monolayer hexagonal boron nitride by two-color laser field.

We theoretically investigate the high-order harmonic generation (HHG) of the monolayer hexagonal boron nitride by two-color laser pulses, based on the abinitio time-dependent density-functional theory. We find that the waveform of the two-color laser field can dramatically control the harmonic spectrum. The two-color laser field can enhance the harmonic radiation more efficiently than the monochromatic pulse laser with the same incident energy. We investigate the influence of incident laser pulse parameters on the harmonic radiation, such as the relative phase of the two-color field, the amplitude ratio between component electric fields, and the laser orientation. We show that the HHG spectrum is controlled by both the electric field and the vector potential. The electronic band structure and the laser-matter energy transfer play an important role in determining the laser polarization for optimal HHG in the hBN crystal. Our work supplies a scheme to manipulate HHGs in two-dimensional materials and provides a potential methodology for the generation of intense extreme-ultraviolet pulses.

A study of a silicone film deposited on quartz glass under laser radiation

The paper studies the structure, optical and operational properties of a silicone film deposited on the surface of quartz glass as a result of the action of laser radiation on volatile substances released from a silicone rubber sample in a closed volume. The research was carried out within the framework of the laser multiparameter method and using an original setup, which includes a solid-state neodymium laser with a wavelength of 1064 nm, and laser pulse parameters: energy of 105 mJ, a duration of 11–14 ns, a repetition rate of 10 Hz. A sealed test-cuvette is placed at the output of the laser. A silicone rubber sample is placed inside the test-cuvette. When laser radiation passes through the test-cuvette, volatile substances that are released from the sample over time interact with the laser radiation and create deposition zones on the optical elements of the test-cuvette, which affect the optical characteristics of these optical elements. The topology of the deposition zones was studied using a profilometer. The structural composition of the original silicone rubber and the deposition zone was determined using a scanning electron microscope. The main results show the dependences of the coefficients of the area and attenuation of the deposition zone on the temperature and the number of laser pulses. The elemental composition, color, resistance to the action of the solvent, and the thickness of the deposition zones have been investigated. It was found that with an increase in the temperature and the number of laser pulses, the area and attenuation coefficients of the deposition zones increase, the color does not change, and the resistance to the action of the solvent increases. With an increase in temperature, the deposition zone, initially consisting of micro-fragments, becomes continuous, and with an increase in the number of laser pulses, its thickness increases. The thickness of the deposition zone is unevenly distributed along its diameter. The results obtained can be applied in the development of silicone-containing biochips for health diagnostics and therapy.

Polarisation-dependent single-pulse ultrafast optical switching of an elementary ferromagnet

The ultimate control of magnetic states of matter at femtosecond (or even faster) timescales defines one of the most pursued paradigm shifts for future information technology. In this context, ultrafast laser pulses developed into extremely valuable stimuli for the all-optical magnetization reversal in ferrimagnetic and ferromagnetic alloys and multilayers, while this remains elusive in elementary ferromagnets. Here we demonstrate that a single laser pulse with sub-picosecond duration can lead to the reversal of the magnetization of bulk nickel, in tandem with the expected demagnetization. As revealed by realistic time-dependent electronic structure simulations, the central mechanism involves ultrafast light-induced torques that act on the magnetization. They are only effective if the laser pulse is circularly polarized on a plane that contains the initial orientation of the magnetization. We map the laser pulse parameter space enabling the magnetization switching and unveil rich intra-atomic orbital-dependent magnetization dynamics featuring transient inter-orbital non-collinear states. Our findings open further perspectives for the efficient implementation of optically-based spintronic devices.

Photoacoustic effect in micro- and nanostructures: numerical simulations of Lagrange equations

The work provides the description of theoretical and numerical modeling techniques of thermomechanical effects that take place in absorbing micro- and nanostructures of different materials under the action of pulsed laser radiation. A proposed technique of the numerical simulation is based on the solution of equations of motion of continuous media in the form of Lagrange for spatially inhomogeneous media. This model allows calculating fields of temperature, pressure, density, and velocity of the medium depending on the parameters of laser pulses and the characteristics of micro- and nanostructures.

Laser micro welding with fiber lasers for battery and fuel cell based electromobility

New challenges are arising within the joining processes in the field of electromobility. Joining highly reflective metals and dissimilar materials such as copper and aluminum – often encountered in battery electrical vehicles – is viewed as a challenging task. Additionally, the use of thin sheets of stainless steel is gaining importance in applications with PEM fuel cells, where the welding length is sometimes up to and even more than five meters long, yet the process speed remains limited.Laser micro welding offers in comparison to conventional joining methods several advantages regarding process speed, parts accessibility, potential of automation, and particularly localized heat input. There are different types of lasers available on the market ranging from the visible to the infrared range, yet choosing the right laser depending on the task can be challenging. Several characteristics are considered when comparing weld quality such as surface finish, reproducibility and mechanical stability. Recently, the possibility of tuning the parameters of a nanosecond pulsed fiber laser to achieve welding is being examined. On another topic, using a novel welding strategy with spatial power modulation – by applying a new geometry – is also being investigated. In this paper, the welding process with the nanosecond pulsed fiber laser is evaluated based on mechanical stability and surface finish, which allows further insight into the suitability of such a method for welding particularly copper and aluminum materials. Additionally, some initial results from the here introduced spatial power modulation technique – used to weld stainless steel sheets – are presented.

Generation of single attosecond relativistic electron bunch from intense laser interaction with a nanosphere

Ultrahigh-intensity laser-plasma physics provides unique light and particle beams as well as novel physical phenomena. A recently available regime is based on the interaction between a relativistic intensity few-cycle laser pulse and a sub-wavelength-sized mass-limited plasma target. Here, we investigate the generation of electron bunches under these extreme conditions by means of particle-in-cell simulations. In a first step, up to all electrons are expelled from the nanodroplet and gain relativistic energy from time-dependent local field enhancement at the surface. After this ejection, the electrons are further accelerated as they copropagate with the laser pulse. As a result, a few, or under specific conditions isolated, pC-class relativistic attosecond electron bunches are generated with laser pulse parameters feasible at state-of-the-art laser facilities. This is particularly interesting for some applications, such as generation of attosecond x-ray pulses via Thomson backscattering.

Tuning single-walled aligned carbon nanotubes for optimal terahertz pulse generation through optical rectification of ultrashort laser pulses.

Terahertz radiation by optical rectification in single-walled highly aligned chiral carbon nanotubes (SWCNTs) irradiated by ultrashort laser pulses is comprehensively studied. We take into account the structural properties of SWCNTs, including the filling factor, alignment, and chirality, as well as the laser pulse parameters including the pulse duration and the wavelength. The second-order nonlinear susceptibility tensor and, consequently, polarization responsible for optical rectification in SWCNTs are derived based on symmetrical features.The effective dielectric constants of SWCNTs are also extracted using the effective medium approximation. Then, the propagation effects in terms of the group velocity dispersion and absorption at both pump and terahertz pulse frequency regions are investigated. By adjusting the laser and the structure effective parameters among those practically feasible, minimum velocity mismatch required for optimum optical rectification and coherent amplification at terahertz frequencies in SWCNTs are introduced. Comparing the electric field waveform and the spectrum of the generated terahertz pulses under various conditions reveals that SWCNTs with higher alignment and lower filling factor at chirality (6,4) irradiated by an ultrashort laser pulse with the wavelength of 1550 nm could provide the conditions for maximum terahertz radiation generation.

Control of molecular-field-free orientation steered by asymmetric phase-jump laser pulses

• The molecular orientation with phase-jump laser pulse is investigated by time-dependent quantum wave packet method. • The asymmetry of laser pulse has a significant influence on the orientation. • The molecular orientation is effected by the laser pulse parameters. A theoretical scheme used for manipulating the orientation of LiH molecules with phase-jump laser pulse is proposed. The time-dependent quantum wave packet method is used to numerically compute the wave-function of molecules by including both vibrational and rotational degrees of the freedom. The effect of asymmetric phase jump pulses on molecular orientation can be well understood by a train of HCPs kicking the molecule. The effective orientation of molecules can be achieved by phase-jump laser pulse. The maximal orientation degree, 0.757, and the longest orientation duration, 0.365 ps, are given by optimizing the parameters of phase-jump laser pulse. The molecular orientation is influenced significantly by phase and phase-jump time. Also the molecular orientation is dependent on pulse frequency, peak intensity and system temperature.

Efficiency improvement of the femtosecond laser source of superponderomotive electrons and X-ray radiation due to the use of near-critical density targets

We consider the possibility of improving the superhigh-power laser pulse to superponderomotive electrons energy conversion efficiency by using porous targets of near-critical density. We report the results of numerical simulations based on the typical parameters of laser pulses of the PEARL laser facility built on the principles of parametric chirped pulse amplification (OPCPA). An original scheme for producing a controllable prepulse based on the use of a pump laser switched to a two-pulse regime is discussed. The prepulse is required to homogenise the submicron inhomogeneities of a porous target. Simulations show a significant increase in the laser-to-electron energy conversion efficiency in comparison with solid-state and gas targets. This interaction regime can be used to improve the efficiency of a broad class of laser-driven secondary radiation sources, such as a betatron source, bremsstrahlung, neutron source, etc.

Prominent absorption and luminescence characteristics of novel silver-cinnamon core-shell nanoparticles prepared in ethanol using PLAL method

Some spherical silver-cinnamon core-shell nanoparticles (Ag‒Cin CSNPs) were prepared in ethanol via the pulsed laser ablation in liquid (PLAL) technique. The structure, morphology and optical characteristics of these CSNPs were tailored by tuning the 1064 nm Q-switch Nd:YAG pulse laser parameters. The HR-TEM images manifested the nucleation of the crystalline spherical CSNPs (mean diameter ≈13.18 ± 1.29 nm and lattice spacing ≈0.37 nm) with preferred growth along (111) lattice planes. The thermogravimetric analysis of these CSNPs confirmed their good thermal stability with the total weight loss of 73.8 wt% at 68 °C. The FTIR spectra of the cinnamon capped Ag‒NPs displayed the presence of C–O, CO and amine groups. The molecular π-π* absorption of the produced NPs showed a blue-shift. These CSNPs revealed an enhanced localised surface plasmon resonance (LSPR) absorption and luminescence peaks. The quantum yield of the absorption band (concerted at 409 nm with FWHM ≈96.07 nm) was approximately 0.4323 ± 0.1. The XRD and EDX analyses of the NPs showed their high crystallinity and uniform elemental distribution of O, C and K (in cinnamon covering the Ag‒NPs surface), respectively. It is established that the novel Ag‒Cin CSNPs with the customized properties can be made by controlling the laser parameters which may be useful for various biomedical applications.

Adaptive Nonlinear Phase Compensation in a Femtosecond Hybrid Laser with Varying Pulse Repetition Rate

In this manuscript, an implementation of a tunable nonlinear phase compensation method is demonstrated on a typical femtosecond hybrid laser consisting of a fiber pre-amplifier and an additional solid-state amplifier. This enables one to achieve constant laser pulse parameters over a wide range of pulse repetition rates in such a laser. As the gain in the solid-state amplifier is inversely proportional to the input power, the shortfall in the solid-state gain at higher repetition rates must be compensated for with fiber pre-amplifier to ensure constant pulse energy. This increases the accumulated nonlinear phase and consequently alters the laser pulse parameters such as pulse duration and Strehl ratio. To overcome this issue, the nonlinear phase must be compensated for, and what is more it should be compensated for to a different extent at different pulse repetition rates. This is achieved with a tunable CFBG, used also as a pulse stretcher. Using this concept, we demonstrate that constant laser pulse parameters such as pulse energy, pulse duration and Strehl ratio can be achieved in a hybrid laser regardless of the pulse repetition rate.

Specific features of radiation emitted upon tunnel ionisation of atoms in extremely intense laser fields

Radiation emitted by fast electrons in the process of multiple tunnel ionisation of heavy atoms in the focus of a laser pulse with extreme intensity exceeding 1022 W cm−2 is studied. It is shown that the spectral-angular distribution of emitted photons in a wide range of angles is qualitatively determined by relations of the synchrotron radiation theory. The dependences of the number and the characteristic frequency of emitted photons on the laser pulse parameters are estimated. The obtained results can be used to determine the maximum laser intensity in the focus.

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.

Influence mechanism of the keyhole behavior on penetration depth by in-situ monitoring in pulsed laser welding of aluminum alloy

The dynamic behavior of keyhole plays a critical role in determining the weld penetration and process stability during pulsed laser welding of thin-sheet aluminum alloy. This study aimed to explore the influence mechanism of the keyhole instability on the penetration depth under different pulsed laser parameters. To this end, we firstly applied a high-speed camera to directly observe the oscillation characteristic of inner keyhole through a transparent glass, and its fluctuation period was nearly coincided with one pulse duration. Based on maximum deviation ratio, the pulse frequency has a more obvious effect on the fluctuation in keyhole depth comparing with laser power and focus distance. Along with the increase of laser power and frequency, the incident laser intensity also increased, which leads to an increasing of keyhole depth and decreasing of inclination angle. The weld penetration depth is determined primarily by the variation of the keyhole depth and inclination angle. The findings of this paper will provide theoretical basis for achieving the desired weld penetration and improving weld quality regarding keyhole formation.

Modulating self-similar vector bisolitons

We simulate the modulation of 1-μm self-similar (parabolic) vector bisolitons in this paper. Through the change of laser pulse parameters in orthogonal directions, we modulate self-similar vector bisoliton when its polarization or group velocity is locked. When input orthogonal vector components have the same central wavelength, the variation of projection angle can induce the variation of time delay, and the change of phase difference can induce the change of amplitude ratio of output vector solitons. By comparison, for input orthogonal vector components with slightly different central wavelengths, pulse shapes with oscillations can be achieved at some specific condition. Our simulation results expand the research about vector soliton manipulation and are beneficial for relevant experiments.

Energy limit for linear-to-nonlinear femtosecond laser pulse focusing in air

Propagation of a tightly focused high-power ultrashort laser pulse in an optical medium is usually substantially influenced by the medium optical nonlinearity that can noticeably affect the laser pulse parameters around the nonlinear focus and lead to unavoidable and often undesirable spatial distortions of the focal waist. We present the results of our experimental study and numerical simulations on a femtosecond Ti:Sapphire laser pulse propagation in air under different spatial focusing. We concentrated our study on spectral-angular and spatial pulse transformations under different focusing regimes - from linear to nonlinear one, when pulse filamentation occurs. For the first time to the best of our knowledge, we found the laser pulse numerical apertures range – namely, from NA = 2·10-3 to 5 10-3(for the laser pulse energy of 1 mJ), where the laser pulse distortions both in frequency-angular spectrum and pulse spatial shape are minimal. By means of the numerical simulations, we found the threshold pulse energy and peak power in a wide range of focusing conditions, within which a transition between the linear and strongly nonlinear laser pulse focusing in air takes place. This energy limit is shown to decrease with pulse numerical aperture enhancement. Our findings identify the laser pulse numerical apertures and energes adequate for getting a maximum laser intensity with a good beam quality around the focal point suitable for various laser micropatterning and micromachining technologies.

Deterministic generation of high-dimensional entanglement between distant atomic memories via multiphoton exchange

Promising access to high-speed quantum networks relies on the creation of high-dimensional entangled memories that provide quantum communication with higher capacity of noisy quantum channels, thereby reducing the transmission time of information. Yet, the distribution of multidimensional entanglement between remote memory nodes is still faintly investigated. We propose an experimentally feasible protocol of deterministic generation of high-dimensional entanglement between distant multilevel atoms confined in high-finesse optical cavities and driven by laser pulses. Three-dimensional entanglement is generated deterministically between remote atoms by triggering a two-photon wave packet, which mediates a superposition of states chosen by the laser pulse parameters. The efficient transfer of atomic states between remote nodes allows the construction of a three-dimensional quantum repeater, where the successful creation of entanglement can be verified by a simple method for reliable measurement of atomic ground Zeeman states.