Parametric attosecond pulse amplification far from the ionization threshold from high order harmonic generation in He⁺

Abstract

Parametric amplification of attosecond coherent pulses around 100 eV at the single-atom level is demonstrated for the first time by using the 3D time-dependent Schrödinger equation in high-harmonic generation processes from excited states of He +. We present the attosecond dynamics of the amplification process far from the ionization threshold and resolve the physics behind it. The amplification of a particular central photon energy requires the seed XUV pulses to be perfectly synchronized in time with the driving laser field for stimulated recombination to the He + ground state and is only produced in a few specific laser cycles in agreement with the experimental measurements. Our simulations show that the amplified photon energy region can be controlled by varying the peak intensity of the laser field. Our results pave the way to the realization of compact attosecond pulse intense XUV lasers with broad applications.

Localized Core Four-Wave Mixing Buildup in the X-ray Spectrum of Chemical Species

“…Nonlinear processes that have long been studied in the infrared and optical regions are being extended to the X-ray region of the electromagnetic spectrum as a result of recent advances in the generation of coherent X-ray pulses in synchrotron and free-electron lasers (FEL), and in high-harmonic generation (HHG). − Bright trains of femtosecond pulses are routinely produced and used in a wide range of areas such as materials science and biochemistry. The pulses in the trains produced in these sources ordinarily have a random phase and this aspect is exploited in the present work.…”

“…The relative phase between ω and 3ω pulses is given by ϕ n , with calculations performed for ϕ n increasing from 0 to 2π rad by π/5 rad steps. The pulse pair given in eq can describe the output of a seeded FEL pulse and also the output from parametrically amplified HHG pulses . In these cases, the phase between different harmonics can in principle be controlled, and therefore, there is also the option of scanning the phase.…”

Resonantly-Enhanced Difference-Frequency Generation in the Core X-ray Absorption of Molecules

“…Selective photodissociation of molecules by resonant excitation near a chosen core ionization edge by means of nonlinear interactions in the X-ray range is becoming conceivable due to recent advances in the development of intense ultrashort X-ray coherent pulse sources, such as synchrotron, free-electron lasers (FEL) and in high-harmonic generation. [1][2][3][4][5][6][7][8][9][10] Several nonlinear interactions in the X-ray range are accordingly being investigated. 11 In a previous work 12 we showed how the phasesensitivity cancellation of the anti-Stokes component previously described in two-and threelevel systems in the infrared and optical regions can be extended to the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) 6 of chemical species by highly localized four-wave mixing (FWM) nonlinear processes.…”

“…Based on these results, we anticipate that highly selective excitation by re-DFG X-ray nonlinear processes might be achieved in more complex molecular systems and bulk materials by using highly penetrating two-color hard X-ray pulses, with extensive applications.Selective photodissociation of molecules by resonant excitation near a chosen core ionization edge by means of nonlinear interactions in the X-ray range is becoming conceivable due to recent advances in the development of intense ultrashort X-ray coherent pulse sources, such as synchrotron, free-electron lasers (FEL) and in high-harmonic generation. [1][2][3][4][5][6][7][8][9][10]…”

“…Selective photodissociation of molecules by resonant excitation near a chosen core ionization edge by means of nonlinear interactions in the X-ray range is becoming conceivable due to recent advances in the development of intense ultrashort X-ray coherent pulse sources, such as synchrotron, free-electron lasers (FEL) and in high-harmonic generation. [1][2][3][4][5][6][7][8][9][10]…”