High-power Ultrashort Laser Research Articles

Soliton solutions for generalized quasilinear Schrödinger equations

By introducing a new variable replacement, we study the existence of nontrivial solutions for generalized quasilinear Schrödinger equations which appear from plasma physics, as well as high-power ultrashort laser in matter.

Recent progress in investigation and application of dissipative soliton in fiber lasers

Fiber lasers have promoted the development of scientific researches and technology applications for their excellent beam quality, high efficiency, compact structure, and high reliability. Ultra-short high-energy pulse fiber lasers can find important applications in the areas of optic communication, sensing, precision machining, material processing, ultra-fast diagnosis, biomedicine, and national defense. Consequently, how to increase the power and energy of the laser pulse, control and utilize the complex nonlinearity, and develop the key technologies for the applications of high-power, high-energy, and ultra-broadband all-fiber ultra-short pulse lasers become the important scientific issues for the exploration of new phenomena and schemes as well as the breakthrough of technical systems about fiber laser pulses. This article briefly reviews some key techniques and important progresses about mode-locked fiber lasers, discusses the merits and drawbacks of various fiber lasers and pulses, also introduces our research results in the past several years about how to improve the performance of fiber lasers and achieve novel kinds of pulses. We particularly discuss the typical behaviors of fiber lasers operating in different dispersion regimes, and demonstrate both experimentally and numerically the formation mechanisms, output features, and dynamic evolutions of conventional solitons as well as dissipative solitons. Moreover, several novel types of high-energy wave-breaking-free pulses are introduced. These results in the article may provide helpful theoretical and experimental fundamentals for the in-depth study of new high-energy pulses. Hopefully, our introductions and discussions can attract the researchers’ attentions to the exploration of new phenomena and mechanisms of ultra-short high-energy pulses based on novel mode-lockers, and bring the new understandings about nonlinear phenomenon of ultra-short high-energy pulses under extreme conditions.

Nonlinear propagation of light in structured media: Generalized unidirectional pulse propagation equations

Unidirectional pulse propagation equations [UPPE, Phys. Rev. E 70, 036604 (2004)] have provided a theoretical underpinning for computer-aided investigations into dynamics of high-power ultrashort laser pulses and have been successfully utilized for almost a decade. Unfortunately, they are restricted to applications in bulk media or, with additional approximations, to simple waveguide geometries in which only a few guided modes can approximate the propagating waveform. The purpose of this work is to generalize the directional pulse propagation equations to structures characterized by strong refractive index differences and material interfaces. We also outline a numerical solution framework that draws on the combination of the bulk-media UPPE method with single-frequency beam-propagation techniques.

Numerical analysis of the As2Se3 chalcogenide glass multi-ring photonic crystal fiber

A novel kind of As2Se3 chalcogenide glass multi-ring photonic crystal fiber is proposed. The characteristics of multi-ring photonic crystal fiber have been studied by the finite element method. Compared with another two kinds of single-core photonic crystal fibers, the multi-ring PCF can make the perfect combination of the effective mode area, the nonlinearity coefficient and multi-zero dispersion. It can achieve high power supercontinuum generation in middle infrared band; It also can be used in high-power pulsed laser fiber amplifier and high-power ultra-short pulse laser transmission in far infrared band.

Beyond the variable wavelength interferometry—Monitoring the interaction between the ultrashort high power laser pulses and light propagating medium

This paper presents the Variable Wavelength Interferometry (VAWI) technique, its applications and expected research potential of this system equipped with a femtosecond laser. The system is configured for observation and measurement of local optical parameters modified by a high power laser pulse. The VAWI measurement technique has a unique feature that can visualize and enables investigation of the immediate matter response to a single high power laser pulse just in the pulse area, which can locally modify dielectric and optical parameters of matter along the propagation path. It affects the dielectric tensor, refractive indices and it may induce birefringence. The high power laser pulse is responsible for the nonlinear effects in the optical materials like crystals, photonic crystals, optical fibers etc. The VAWI provides the ability to measure very accurately the above optical parameters along the laser pulse propagation path and neighboring regions in the VIS-NIR spectral ranges.

High peak power and sub-picosecond Fourier-limited pulse generation from passively mode-locked monolithic two-section gain-guided tapered InGaAs quantum-dot lasers

We report on the development of a new generation of high-power ultrashort pulse quantum-dot lasers with tapered gain section. Two device designs are proposed and fabricated, with different total lengths and absorber-to-gain-section length-ratios. These designs have been informed by numerical simulations of the dynamic mode-locking regimes and their dependence on the structural parameters. One device design demonstrated a record-high peak power of 17.7 W with 1.26 ps pulse width and a second design enabled the generation of a Fourier-limited 672 fs pulse width with a peak power of 3.8 W. A maximum output average power of 288 mW with 28.7 pJ pulse energy was also attained. In addition, the integrated timing jitter of 2.6 ps and far-field patterns are demonstrated.

A new method for measuring the pulse-front distortion of arbitrary shapes in high-power ultrashort laser systems

We present a new method that can be used to calculate pulse-front distortion by measuring the spectral interference of two point-diffraction fields in their overlapped district. We demonstrate, for the first time, the measurement of the pulse-front distortion of the pulse from a complex multi-pass amplification system, which exists in almost all high-power laser systems, and obtain the irregular pulse-front distribution. The method presented does not need any reference light or assumption about the pulse-front distribution, and has an accuracy of several femtoseconds.

高功率超短激光脉冲特性的三阶相关测量

高功率超短激光脉冲特性的三阶相关测量

Characteristics of filaments at high-power femtosecond laser radiation propagation in air and water: II. Numerical simulation

The results of numerical solution of the nonlinear Schrodinger equation modeling nonstationary self-focusing and filamentation of high-power ultra-short laser radiation in atmospheric air and water are presented. The comparison of the major characteristics of the light and plasma filaments formed in these media is carried out.

Growth and spectroscopic properties of Yb:Lu 1.5Y 1.5Al 5O 12 mixed crystal

Yb 3+-doped (Lu 0.5Y 0.5) 3Al 5O 12 (Yb:LuYAG) single crystal has been grown by the Czochralski method. The segregation coefficient of Yb 3+ was studied by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method. The crystal structure has been determined by X-ray diffraction analysis. The absorption and emission spectra and fluorescence lifetime of Yb:LuYAG crystal were measured at room temperature. The spectroscopic parameters of Yb:LuYAG crystal were compared with those of Yb:YAG and Yb:LuAG crystals with the same doping level. The results indicate that Yb:LuYAG crystals are potential candidates for high-power ultrashort pulse lasers.

Acceleration of light ions from an expanding ultrathin foil of complex ion composition

The problem of the Coulomb explosion of a thin homogeneous foil with light and heavy ions is solved analytically in the context of laser ion acceleration. Spatiotemporal and spectral distributions of the accelerated light ions are obtained. The ions parameters are calculated as functions of the atomic composition of the target. It is shown that, in the interaction between high-power ultrashort high-contrast laser pulses and thin foils with light impurity ions, it is possible to produce accelerated ion bunches that contain a significant fraction of the total number of particles and have a small energy spread (≲10%).

Shaper-assisted removal of the direction-of-time ambiguity in second-harmonic generation frequency-resolved optical gating

We report on a practical method where a pulse shaper in combination with second-harmonic generation frequency-resolved optical gating (SHG-FROG) is used to fully characterize ultrashort laser pulses. The original pulse is modified by adding a small satellite, which allows us to determine the direction of time of the retrieved pulse. The setup extends the work of Zeek et al (2002 Appl. Phys. B 74 S265) to more arbitrary pulse structures. Moreover, it is demonstrated that the method is applicable also in high-power ultrashort laser systems, where the pulse former has to be placed before the chirped-pulse amplifier. We found that the amplitude of the satellite must be smaller than 20% of that of the original pulse to avoid nonlinear distortions.

Stimulated Raman Side Scattering in Laser Wakefield Acceleration

Stimulated Raman side scattering of an ultrashort high power laser pulse is studied in experiments on laser wakefield acceleration. Experiments and simulations reveal that stimulated Raman side scattering occurs at the beginning of the interaction, that it contributes to the evolution of the pulse prior to wakefield formation, and also that it affects the quality of electron beams generated. The relativistic shift of the plasma frequency is measured.

Relativistic laser pulse compression in plasmas with a linear axial density gradient

The self-compression of a relativistic Gaussian laser pulse propagating in a non-uniform plasma is investigated. A linear density inhomogeneity (density ramp) is assumed in the axial direction. The nonlinear Schrödinger equation is first solved within a one-dimensional geometry by using the paraxial formalism to demonstrate the occurrence of longitudinal pulse compression and the associated increase in intensity. Both longitudinal and transverse self-compression in plasma is examined for a finite extent Gaussian laser pulse. A pair of appropriate trial functions, for the beam width parameter (in space) and the pulse width parameter (in time) are defined and the corresponding equations of space and time evolution are derived. A numerical investigation shows that inhomogeneity in the plasma can further boost the compression mechanism and localize the pulse intensity, in comparison with a homogeneous plasma. A 100 fs pulse is compressed in an inhomogeneous plasma medium by more than ten times. Our findings indicate the possibility for the generation of particularly intense and short pulses, with relevance to the future development of tabletop high-power ultrashort laser pulse based particle acceleration devices and associated high harmonic generation. An extension of the model is proposed to investigate relativistic laser pulse compression in magnetized plasmas.

Propagation of a high-power ultrashort laser pulse along a horizontal atmospheric path

Experimental results of the study of the evolution of the spatial profile and frequency spectrum of terawatt ultrashort Ti: Sa laser pulses propagating along atmospheric paths in the self-focusing mode are presented. The dependence of the laser radiation energy characteristics at the receiving plane on its initial peak power is determined. The tendency of an increase of the laser beam’s angular size and spectral width when increasing its output power is stated. The obtained regularities have been interpreted qualitatively and quantitatively based on the numerical calculations performed in the framework of the model of the nonstationary self-action of an ultrashort light pulse in air. The ob tained results are compared to the results of the authors’ earlier laboratory experiments on the filamentation of focused laser femtosecond radiation.

Optimization design of an ultrabroadband, high-efficiency, all-dielectric grating

More than 97% flat-top diffraction efficiency in the -1st-order TE polarization over a 110 nm wavelength range around 800 nm in an all-dielectric grating is designed by a simulated annealing algorithm and the Fourier mode method. Its band is near to the maximum bandwidth provided by a dielectric high-reflectivity mirror under the match layer. This result will provide a way for high-efficiency chirped-pulse amplification to be used in an ultrashort high-power pulse laser system based on all-dielectric gratings. Furthermore, an effective method for broadband high-efficiency all-dielectric grating design is presented in this Letter.

Laser acceleration of light ions from a thin homogeneous foil of complex atomic composition

A model of the acceleration of light impurity particles from a plane ultrathin foil of complex ion composition by a high-power ultrashort high-contrast laser pulse is proposed. A study is made of both purely Coulomb ion acceleration, typical of extremely high electron energies, and ion acceleration under the conditions of space charge separation, determined by the finite typical electron temperature. Exact and approximate analytic approaches to describing impurity particle acceleration are developed. The spatial and spectral parameters of accelerated light particles are obtained, and their dynamics is investigated as a function of their relative charge density in a model of test impurity particles and in a model in which their own electrostatic field is taken into account. Optimum conditions for the generation of quasi-monoenergetic ions are discussed, depending on the laser radiation parameters and target composition.

Laser acceleration of light impurity from an ultrathin foil of complex ionic composition

The model of acceleration of light impurity particles from a planar ultrathin foil of complex ionic composition under an ultrashort high-power high-contrast laser pulse is proposed. Both the mode of pure Coulomb acceleration of ions, characteristic of extremely high electron energies, and acceleration under conditions of spatial charge separation controlled by a finite characteristic electron temperature are studied. Accurate and approximate analytical approaches for describing impurity particle acceleration are formulated. Spatial and spectral characteristics of accelerated particles are determined. Particle dynamics is studied in both the approximation of test impurity particles and taking into account their intrinsic electrostatic field, depending on the relative charge density of light particles.

Compositional Dependence of g-Factor and Damping Constant of GdFeCo Amorphous Alloy Films

Time-domain magnetization dynamics of sputtered GdFeCo (30 nm) amorphous alloy films was measured by pump-probe method using high-power ultra-short pulse fiber laser. The effective g-factor g eff and effective damping constant alphaeff of the GdFeCo films were estimated by using a numerical calculation of Landau-Lifshitz-Gilbert equation. The precessional frequency took a maximum near the magnetization compensation composition C M of the GdFeCo, while the estimated g eff and alphaeff increased around the angular momentum compensation composition C A. The compositional dependences of g eff and alphaeff were roughly described by a mean-field model. The g eff and alphaeff were also estimated from the ferromagnetic resonance (FMR) spectra, and the data from the FMR spectra agreed well with those from the pump-probe measurement except for the composition near C M. The FMR method was unable to excite the magnetization near C M because of the small net magnetization.

Coulomb explosion of a cluster with a complex ion composition

The problem of the Coulomb explosion of a homogeneous cluster with light and heavy ions has been analytically solved. The space-time and spectral distributions of accelerated ions have been obtained. The characteristics of scattered light ions are determined as functions of the atomic composition of the cluster. It has been shown that sources of monoenergetic ions can be created using the interaction of high-power ultrashort laser pulses with molecular clusters.