Nonlinear Chirped Pulse Research Articles

Field-free orientation of 7LiH steered by a few-cycle nonlinearly chirped pulse

We demonstrate theoretically that an efficient field-free molecular orientation of 7LiH molecule steered by a few-cycle nonlinearly chirped laser pulse with frequency in the terahertz regime can be achieved. The frequency modulation parameter β plays an important role in the molecular orientation, the maximum molecular orientation |〈cosθ〉|max is 0.848 and the orientation duration is 150 fs when β=7.25. In the range of electric-field peak intensity E0=[0.1,4.0] MV/cm, we can find the maximum orientation degree in both positive and negative directions. Compared to the scheme steered by a normal laser pulse, we can find that a more efficient molecular orientation and a smaller difference in population between the adjacent states can be realized by using the nonlinearly chirped laser pulse under the same near-single-period conditions. In addition, at the same temperature, a higher molecular orientation and a smaller decrease rate of orientation with temperature can be obtained by the nonlinearly chirped laser pulse.

Control of the spider-like interference structure in photoelectron momentum distributions of a helium atom in a few-cycle nonlinear chirped laser pulse.

We investigate theoretically the photoelectron momentum distributions (PMDs) of the helium atom in the few-cycle nonlinear chirped laser pulse. The numerical results show that the direction of the spider-like interference structure in PMDs exhibits periodic variations with the increase of the chirp parameter. It is illustrated that the direction of the spider-like interference structure is related to the direction of the electron motion by tracking the trajectories of the electrons. We also demonstrate that the carrier-envelope phase can precisely control the opening of the ionization channel. In addition, we investigate the PMDs when a chirp-free second harmonic (SH) laser pulse is added to the chirped laser field, the numerical results show that the interference patterns can change from only spider-like interference structure to both spider-like and ring-like interference structures.

A Scalable, High-Efficiency, Low-Energy-Spread Laser Wakefield Accelerator Using a Tri-Plateau Plasma Channel.

The emergence of multi-petawatt laser facilities is expected to push forward the maximum energy gain that can be achieved in a single stage of a laser wakefield acceleration (LWFA) to tens of giga-electron volts, which begs the question-is it likely to impact particle physics by providing a truly compact particle collider? Colliders have very stringent requirements on beam energy, acceleration efficiency, and beam quality. In this article, we propose an LWFA scheme that can for the first time simultaneously achieve hitherto unrealized acceleration efficiency from the laser to the electron beam of >20% and a sub-1% energy spread using a stepwise plasma structure and a nonlinearly chirped laser pulse. Three-dimensional high-fidelity simulations show that the nonlinear chirp can effectively mitigate the laser waveform distortion and lengthen the acceleration distance. This, combined with an interstage rephasing process in the stepwise plasma, can triple the beam energy gain compared to that in a uniform plasma for a fixed laser energy, thereby dramatically increasing the efficiency. A dynamic beam loading effect can almost perfectly cancel the energy chirp that arises during the acceleration, leading to the sub-percent energy spread. This scheme is highly scalable and can be applied to petawatt LWFA scenarios. Scaling laws are obtained, which suggest that electron beams with parameters relevant for a Higgs factory could be reached with the proposed high-efficiency, low-energy-spread scheme.

Laser wakefield and direct laser acceleration of electron by chirped laser pulses

Chirped laser pulses are investigated theoretically for laser wakefield (LW) and direct laser (DL) acceleration of electrons in the plasma-bubble regime. Chirping of laser pulse with a suitable frequency allows a better trapping of electron in bubble regime which enforces a strong betatron resonance inside the plasma bubble. Linear and non-linear effects of frequency chirp determine electron acceleration, de-phasing, beam quality in terms of energy spread and high energy from the direct laser field and its plasma wake in bubble regime. Gaussian chirped laser pulse exhibit high energy to the electrons compared with linear and other non-linear chirped pulses in plasma-bubble regime. The investigation with chirped laser pulse opens new dimension to hybrid LW-DL acceleration mechanism in bubble regime.

Chirped optical solitons having polynomial law of nonlinear refractive index with self-steepening and nonlinear dispersion

We demonstrate the existence of chirped solitary waves in cubic-quintic-septimal materials under the influence of the Raman and self-steepening effects. We find new types of localized wave solutions that are characterized by an intensity-dependent frequency chirp, including dark and bright solitary waves. The nonlinearity in the frequency chirp associated with these localized pulses originates from the Raman and self-steepening processes. The formation of these nonlinearly chirped pulses is derived from parametric conditions. Effects of nonlinear parameters on the frequency chirp are discussed as well. The magnitude of the chirp can be efficiently governed by varying the self-steepening and Raman parameters.

Chirped self-similar solitary waves in optical fibers governed with self-frequency shift and varying parameters

We demonstrate that when self-frequency shift effect is the dominant higher-order nonlinear process affecting ultrashort light pulse propagation in an inhomogeneous optical fiber media, a novel class of self-similar solitary waves that are characterized by a nonlinear chirp existed. The solitary wave profiles are of bright, dark, kink, and gray type, illustrating the potentially rich set of chirped self-similar pulses in the inhomogeneous fiber system. Compared with the cubic nonlinear Schrödinger equation with distributed coefficients, the phase of these chirped pulses exhibits a nonlinear structure which makes them more suitable for diverse physical applications. The application of obtained chirped self-similar pulses is also discussed in a periodic distributed amplification system. The results show that one may control the propagation dynamics of the presented nonlinearly chirped pulses by an appropriate choice of the dispersion and nonlinearity parameters.

Direct electron acceleration by chirped laser pulse in a cylindrical plasma channel**Project supported by the National Natural Science Foundation of China (Grant Nos. 11865014, 11765017, 11764039, 11475027, 11274255, and 11305132),the Natural Science Foundation of Gansu Province of China (Grant No. 17JR5RA076), the Scientific Research Project of Gansu Higher Education of China (Grant No. 2016A-005), the Natural Science Foundation of Education

We study the dynamics of single electron in an inhomogeneous cylindrical plasma channel during the direct acceleration by linearly polarized chirped laser pulse. By adjusting the parameters of the chirped laser pulse and the plasma channel, we obtain the energy gain, trajectory, dephasing rate and unstable threshold of electron oscillation in the channel. The influences of the chirped factor and inhomogeneous plasma density distribution on the electron dynamics are discussed in depth. We find that the nonlinearly chirped laser pulse and the inhomogeneous plasma channel have strong coupled influence on the electron dynamics. The electron energy gain can be enhanced, the instability threshold of the electron oscillation can be lowered, and the acceleration length can be shortened by chirped laser, while the inhomogeneity of the plasma channel can reduce the amplitude of the chirped laser.

High-Peak-Power Femtosecond Pulse Generation by Nonlinear Compression in a Yb-Doped Hybrid Fiber

We demonstrate a Yb-doped hybrid fiber with anomalous dispersion in the 1 μm spectral range, where asymptotically single-mode behavior is achieved with a differential mode amplification technique. The fiber has a dispersion of 70-100 ps/(nm·km) in the spectral range from 1.020 μm to 1.055 μm and a sharp dispersion peak (approximately 400 ps/(nm·km) near 1.064 μm) caused by the modes anti-crossing. The relatively large hybrid mode field diameter (8 μm) allows us to demonstrate high-peak-power femtosecond pulse generation via nonlinear chirped pulse compression in both dispersion regimes. Operation near 1.064 μm allows us to compress narrowband (3 dB spectral width of 2 nm) 6 ps pulses down to a duration of 250 fs with a peak power of 3.3 kW. Operation in the spectral region with a nearly constant anomalous dispersion is found to be optimal for the compression of wideband pulses. In particular, 1 ps pulses centered at 1.03 μm with a spectral width of approximately 11 nm are compressed down to 90 fs with a peak power of approximately 10 kW, which to the best of our knowledge is the best result for all-fiber (i.e., without external bulk compressors) systems operating near 1 μm.

Wakefield generation by chirped super-Gaussian laser pulse in inhomogeneous plasma

We study the effect of nonlinearly chirped super-Gaussian (SG) laser pulse on wakefield generation in an inhomogeneous plasma. The different types of nonlinearly chirped pulse are employed, and different kinds of inhomogeneous plasma density are used. The maximum wakefield amplitude as the function of nonlinearly chirped laser pulse and inhomogeneous plasma density in parameter space are obtained. Moreover, the dependence of the maximum wakefield amplitude on the SG laser pulse index is discussed. This shows that a larger wakefield can be obtained when the chirped pulse and inhomogeneous density are in the critical regions. Wakefield generation can be controlled by adjusting the chirped SG pulse and inhomogeneous plasma density parameters. That is, we provide an efficient way for the controlled generation of the wakefield.

Two-qubit gates using adiabatic passage of the Stark-tuned Förster resonances in Rydberg atoms

We propose schemes of controlled-Z and controlled-NOT gates with ultracold neutral atoms based on deterministic phase accumulation during double adiabatic passage of the Stark-tuned F\"{o}rster resonance of Rydberg states. The effect of deterministic phase accumulation during double adiabatic passage in a two-level quantum system has been analyzed in detail. Adiabatic rapid passage using nonlinearly chirped pulses with rectangle intensity profile has been discussed. Nonlinear time dependence of the energy detuning from the F\"{o}rster resonance is used to achieve a high fidelity of population transfer between Rydberg states. Fidelity of two-qubit gates has been studied with an example of the $90S+96S\to 90P+95P$ Stark-tuned F\"{o}rster resonance in Cs Rydberg atoms.

High-Average-Power Polarization Maintaining All-Fiber-Integrated Nonlinear Chirped Pulse Amplification System Delivering Sub-400 fs Pulses

We experimentally demonstrate a monolithic single polarization nonlinear chirped pulse amplification (CPA) system producing high-average-power femtosecond pulses operating at 1.06 μm. Thanks to the fiber-based components and standard fiber splicing techniques, the system is nearly fully fiberized, except for the bulk grating pulse compressor. The main fiber amplifier delivers chirped picosecond pulses with average power of 193 W, repetition rate of 80 MHz, and duration of 209 ps. The pulse compressor is designed using high line density transmission gratings to keep small grating separation for the consideration of compactness and simplicity. After pulse compression, femtosecond pulses with average power of 119 W, duration of 352 fs, and peak power of 4.2 MW are obtained. The compression efficiency is 61.5%, limited by the diffraction efficiency of transmission gratings. Even so, to our knowledge, this is the highest average power ever reported in fiber CPA systems with a fiber-based stretcher. The mismatched third-order dispersion between fiber stretcher and bulk optical grating compressor is successfully compensated via optimization of the total nonlinear phase shift in the fiber amplifier chain.

Analysis of radial and longitudinal force of plasma wakefield generated by a chirped pulse laser

In present paper, the chirp effect of an electromagnetic pulse via an analytical model of wakefield generation is studied. Different types of chirps are employed in this study. Our results show that by the use of nonlinear chirped pulse the longitudinal wakefield and focusing force is stronger than that of linear chirped pulse. It is indicated that quadratic nonlinear chirped pulses are globally much efficient than periodic nonlinear chirped pulses. Our calculations also predict that in nonlinear chirped pulse case, the overlap of focusing and accelerating regions is broader than that achieved in linear chirped pulse.

Ultrafast optical switching in quantum dot-metallic nanoparticle hybrid systems.

We study ultrafast excitonic population inversion resulting from the interaction of a semiconductor quantum dot (SQD) with localized surface plasmons. The plasmonic enhanced fields are generated when a metallic nanoparticle (MNP) is subject to a nonlinear chirped few-cycle pulse train. By numerically solving the time-dependent Bloch equations beyond the rotating-wave approximation, we show that the complete population inversion can be achieved for small interparticle distance and the dynamic in population inversion exhibits a steplike transition between absorption and amplifying. This phenomenon can be exploited as an all-optical ultrafast switching device. Moreover, the final state of population inversion is shown to be modified significantly with the interparticle distances, which is not only robust against the variation of probe pulse parameters but also suggests a straightforward method for measuring the interparticle distances via probing the final populations.

Effect of nonlinear chirped Gaussian laser pulse parameters on the electron acceleration

One-dimensional analysis of electron acceleration by a nonlinear chirped Gaussian laser pulse was investigated numerically. Two main nonlinear chirped pulses, polynomial and periodical were used. The maximum energy of electron in nonlinear chirped is approximately three times more than that of linear chirped. In the case of first order nonlinear polynomial chirp, Ω(ξ) = 1 + aξ + bξ2, the electron can be accelerated up to 5.3 GeV. Indeed, the analysis of the electron trajectory in x-z plane showed that the electron in the field of the nonlinear chirped pulse has a much smaller divergence than that of linear chirped pulse.

Effect of nonlinear chirped Gaussian laser pulse on plasma wake field generation

An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wake field which can accelerate charged particles up to GeV energies within a compact space compared to the conventional accelerator devices. In this paper, the effect of different kinds of nonlinear chirped Gaussian laser pulse on wake field generation is investigated. The numerical analysis of our results depicts that the excitation of plasma wave with large and highly amplitude can be accomplished by nonlinear chirped pulses. The maximum amplitude of excited wake in nonlinear chirped pulse is approximately three times more than that of linear chirped pulse. In order to achieve high wake field generation, chirp parameters and functions should be set to optimal values.

The chirp-control of frequency-tunable narrowband terahertz pulses by nonlinearly chirped laser pulse beating

We demonstrate a method for controlling the chirp of the frequency-tunable narrowband terahertz pulses that are generated by photomixing with nonlinearly chirped laser pulse pairs. We find that in a grating-based laser-pulse stretcher, the frequency sweep rates of the generated terahertz pulses can be controlled by simply changing the incident angle. This method is also applicable to other mechanisms of terahertz pulse generation.

Ultra-broadband supercontinuum generation with a nonlinear chirped pulse for controlling quantum path

We theoretically investigate the high-order harmonic generation in helium atom driven by a nonlinear chirped laser pulse with few-cycle duration. By employing appropriate chirp to the driving pulse, an efficient electric field waveform of controlling quantum path for ultra-broadband supercontinuous harmonics is realized, and then an isolated sub-50 as pulse with bandwidth of 739eV can be significantly obtained.

Ultrafast and selective coherent population transfer in four-level atoms by a single nonlinearly chirped femtosecond pulse

We report and propose a simple scheme to achieve the ultrafast and selective population transfer in four-level atoms by utilizing a single frequency chirped few-cycle pulse. It is demonstrated that the almost complete population may be transferred to the preselected state of atoms just by manipulating the so called chirp offset parameter. The robustness of the scheme against the variation of laser pulse parameters is also investigated. The proposed scheme may also be useful for the selective population transfer in molecules.

Isolated sub-100 attosecond pulse generation driven by a multi-cycle chirped laser pulse and a polarization gating

We theoretically investigate the high-order harmonic generation driven by the combination of a multi-cycle nonlinear chirped laser pulse and a polarization gating. On the one hand, the x-component of the polarization gating enlarges the asymmetry of the pulse centre of the chirped laser field, which leads to the extension of the cutoff of the high-order harmonic spectrum; on the other hand, only a few cycles of the combination field centre remain linearly polarized due to the existence of the y-component of the polarization gating, which helps to generate the continuum spectrum. Therefore, in the high-order harmonic spectrum, a very broad continuum spectrum appears even in the multi-cycle regime, from which an isolated sub-100 as pulse could be obtained.

Propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium

We investigate the propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium. For certain chirp strength and chirp width, an incident 2π nonlinear chirped pulse will split into optical precursors and a stable self-induced transparency soliton. This is caused by the particular Fourier spectrum that includes not only central resonant frequency components but also high-frequency and low-frequency sidebands. Moreover, the effects of chirp parameters on the evolution of nonlinear chirped pulses are also discussed.