Strong-field coherent control of isolated attosecond pulse generation

Abstract

Attosecond science promises to reveal the most fundamental electronic dynamics occurring in matter and it can develop further by meeting two linked technological goals related to high-order harmonic sources: improved spectral tunability (allowing selectivity in addressing electronic transitions) and higher photon flux (permitting to measure low cross-section processes). New developments come through parametric waveform synthesis, which provides control over the shape of field transients, enabling the creation of highly-tunable isolated attosecond pulses via high-harmonic generation. Here we demonstrate that the first goal is fulfilled since central energy, spectral bandwidth/shape and temporal duration of isolated attosecond pulses can be controlled by shaping the laser waveform via two key parameters: the relative-phase between two halves of the multi-octave spanning spectrum, and the overall carrier-envelope phase. These results not only promise to expand the experimental possibilities in attosecond science, but also demonstrate coherent strong-field control of free-electron trajectories using tailored optical waveforms.

Optical Waveform Synthesis and Its Applications

“…Already with a 2 µm driver and its SHG at 1 µm, a continuous seeding range of 500 nm to 4 µm can be accessed easily. The separate WLG seeding approach was successfully used in Rossi et al [22] and Yang et al, [23] as we will discuss in Section 3.1.1.…”

“…[204,218] These are: i) strong-field processes can be temporally confined within the most intense half-cycle, thereby allowing for higher time-resolution. ii) The ability to generate IAPs via HHG in different spectral regions, [23] and iii) the coherent control of light-induced dynamics in matter can be realized by sculpting the driving waveform. [23,79,220] Since its first demonstration in 2011, [204] the HWS source described in Section 3.1.4 [17] has been the only WS applied to timeresolved experiments.…”

“…Apart from efforts that seek to maximize the HHG efficiency and energy cutoff, fewer have addressed the additional optimization of the driving waveform for generating energytunable and high-contrast IAPs. [23,[187][188][189] On the one hand, experimental and theoretical studies have shown the possibility of enhancing the yield of selected high-order harmonics regions by one order of magnitude or more by tailoring the driving pulse either using adaptive phase control [58,156] or WS. [190] On the other hand, a number of optical gating techniques [191] have been established that do not require single-or sub-cycle driving pulses to "directly" generate IAPs at the single-atom level.…”

“…This can be an actively CEP-stabilized laser, [19,20] or the CEP-stable output of an OP(CP)A. [21] In other PWS schemes, [22][23][24][25][26] the pulses to be synthesized are amplified via individual OP(CP)As, which amplify a low-energy seed in different nonlinear crystals with large gain. Here, the seed pulses need to be CEP-stable, have a spectrum at least as broad as the gain bandwidth (phase-matching), be as energetic as possible to avoid competing amplification of superfluorescence, and have high shot-to-shot and long-term stability to minimize fluctuations in the synthesized pulses.…”

“…In the opposite scenario, where the strong, fundamental field was fixed at 0.8 µm and a longer-wavelength, weaker field served as the assisting field; HHG enhancements were found only a few times lower than the original 𝜔-3𝜔 optimization. [167] Experimental Works: On the experimental side, many studies have investigated HHG driven by two-and multi-color fields with parallel [6,20,23,77,160,162,[168][169][170][171][172][173][174][175][176][177][178][179][180] or perpendicular [181][182][183][184][185][186] polarizations. In particular, experiments with parallel-polarized fields revealed HHG yield enhancement, energy cutoff extension, attosecond coherent control, and direct IAP generation.…”