Optimization Of High-order Harmonic Generation Research Articles

Optimization of high-order harmonic generation for the time-resolved ARPES

Optimization of high-order harmonic generation for the time-resolved ARPES

Optimization of high-order harmonic generation by optimal control theory: Ascending a functional landscape in extreme conditions

A theoretical optimization method of high-harmonic-generation (HHG) is developed in the framework of optimal-control-theory (OCT). The target of optimization is the emission radiation of a particular frequency. The OCT formulation includes restrictions on the frequency band of the driving pulse, the permanent ionization probability and the total energy of the driving pulse. The optimization task requires a highly accurate simulation of the dynamics. Absorbing boundary conditions are employed, where a complex-absorbing-potential is constructed by an optimization scheme for maximization of the absorption. A new highly accurate propagation scheme is employed, which can address explicit time dependence of the driving as well as a non-Hermitian Hamiltonian. The optimization process is performed by a second-order gradient scheme. The method is applied to a simple one-dimensional model system. The results demonstrate a significant enhancement of selected harmonics, with minimized total energy of the driving pulse and controlled permanent ionization probability. A successful enhancement of an even harmonic emission is also demonstrated.

High-order sum and difference frequency generation using tunable two- and three-color commensurate and incommensurate mid-infrared pumps of graphite plasma

We demonstrate high-order sum and difference harmonic generation using the mixing of tunable (1200–2600 nm) pulses from optical parametric amplifier and 810-nm ultrashort pulses in the extended laser-produced graphite plasma. Optimization of high-order harmonic generation using various parameters (delay between two-color incommensurate and commensurate waves, ratio between pulse intensities, use of parallel and orthogonal polarizations of interacting pulses, etc.) and comparison with a two-color pump using mid-infrared and second-harmonic pulses are presented. We show that, despite the nonoptimal spatiotemporal overlap of two or three sources of radiation in plasma, the application of the proposed technique allows generation of significantly denser combinations of interacting waves, leading to sum and difference frequency generation in the extreme ultraviolet region.

Tunable optimization of high-order harmonic generation driven by 5 fs laser pulses

The characteristics of high-order harmonic generation (HHG) driven by 5 fs laser pulses interacting with argon under tightly focused geometry are investigated in this paper. By carefully optimizing parameters like dispersion, gas pressure and gas cell position, the enhanced HHG with nearly one order of magnitude in a range of 60-73 eV is observed. Based on single atom approximation and Maxwell propagation equations, numerical simulation is conducted to compare with the experimental characterization with proper parameter. It is proved that the phase-matching plays a crucial role in this phenomenon showing that the theoretical results are in agreement with the experimental results.

Time-resolved spectroscopy of plasma plumes: A versatile approach for optimization of high-order harmonic generation in laser plasma

The time-resolved studies of laser-produced Ag, In, Pt, V, Mn, and Ga plasmas are presented from the point of view of plasma application as the nonlinear optical medium for high-order harmonic generation of laser radiation. We show that optimization of plasma formation using this technique allows the enhancement of harmonic generation efficiency and extension of maximal harmonic order.

Systematic study of high-order harmonic optimal control by temporal pulse shaping of laser pulses

We explore experimentally and numerically the physics underlying the optimization of high-order harmonic generation by intense laser pulses, whose temporal profile is tailored by a learning genetic algorithm. Based on a large set of optimization data obtained under different generation parameters, we show that the algorithm converges toward a class of very special profiles on the leading edge of the pulse. The behavior of the harmonic signal is then compared with theoretical simulations based on the time-dependent Schr\"odinger equation, allowing one to identify separately the role of microscopic and macroscopic phenomena in the temporal dynamics of high-harmonic generation and optimization.

Optimization of high-order harmonic generation by adaptive control of a sub-10-fs pulse wave front.

We present a method for the optimization of high-order harmonic generation based on wave-front correction of the driving laser beam. The technique exploits wave-front adaptive control by means of a deformable mirror, governed by an optimization procedure.

Optimization of conversion efficiency and spatial quality of high-order harmonic generation

Optimization of high-order harmonic generation has been studied with a 30 fs laser at an intensity of < 2x10 14 W/cm 2 in a quasi-static gas cell (≤ 10 mm) filled with argon (≤ 90 torr). The effect of propagation length and gas density on the conversion efficiency and spatial quality of high-order harmonics are investigated comprehensively. As a result of phase-matched propagation, both the spatial quality and conversion efficiency of the 29th harmonic are successfully optimized to Gaussian-like profile with a divergence of 4.5 mrad (full width at 1/e 2 maximum) and a saturated efficiency. A quasi-two-dimensional simulation confirms the phase-matching effect.

Optimization of high-order harmonic generation by genetic algorithm and wavelet time-frequency analysis of quantum dipole emission

We present an ab initio three-dimensional quantum study of the coherent control of high-order harmonic generation ~HHG! processes in intense pulsed laser fields by means of the genetic algorithm optimization of the laser-pulse amplitude and phase. Accurate time-dependent wavefunction and HHG power spectrum are obtained by the time-dependent generalized pseudospectral method and wavelet transform is used to obtain the dynamical phase associated with the dipole-emission time profile. It is shown that ‘‘intra-atomic’’ dynamical phase matching on the sub-optical cycle, attosecond, time scale can be achieved, leading to nearly perfect constructive interference between different returning electronic wave packets and marked improvement in both emission intensity and purity of a given harmonic order. The study of coherent control of atomic and molecular processes is a subject of much current interest in science and technology @1#. In particular, temporally shaped ultrashort laser pulses have been successfully used to design welldefined wave packets@2#, and to control multiphoton absorption @3# and chemical reactions @4#, etc. In the area of the interaction of atoms with intense-laser-pulse, high-order harmonic generation ~HHG! of orders as high as 300 has been observed @5,6#, with photon energies in excess of 500 eV. A novel concept of ‘‘intra-atomic’’ phase matching has been recently introduced, allowing the enhancement of the intensity of a specific high harmonic @7#. It is shown that by carefully tailoring the shape of the temporal profile of the driving laser pulse, one can control the time evolution of the electron response to the intense laser field on a sub-opticalcycle, attosecond time scale @7#. A semiclassical model @8,9# is used to interpret these results in terms of the constructive interference in the frequency domain between different electron trajectories @10#, but the effect of atomic structure is not considered. In this Rapid Communication, we present a fully ab initio quantum treatment of the coherent control and enhancement of high-harmonic emission by means of the genetic algorithm ~GA! optimization @11# of the laser-pulse shape and intra-atomic phase matching. We show that by combining the GA search algorithm and accurate quantum solution of the

Optimizing the efficiency in high order harmonic generation optimization by two-color fields

We address the problem of the optimization of high-order harmonic generation by two laser fields of frequencies and respectively, through a theoretical approach. The parameters that are investigated are the two lasers intensities as well as the relative phase between the two fields. We show that a moderate, but significant increase of efficiency can be achieved in that context and give the domain of optimized parameters. Moreover, we quantitatively investigate the gain and set the limitation of the optimization using such coherent control methods.