Sub-half-cycle field transients from shock-wave-assisted soliton self-compression

Abstract

We identify an unusual regime of ultrafast nonlinear dynamics in which an optical shock wave couples to soliton self-compression, steepening the tail of the pulse, thus yielding self-compressing soliton transients as short as the field sub-half-cycle. We demonstrate that this extreme pulse self-compression scenario can help generate sub-half-cycle mid-infrared pulses in a broad class of anomalously dispersive optical waveguide systems. Extremely short, subcycle electromagnetic field waveforms are rapidly emerging as powerful tools for ultrafast optics and photonic technologies 1-3 , enabling an unprecedented, subfemtosecond time resolution in laser spectroscopy 4,5 and an ultimate, subcycle precision in lightwave sculpting 6,7. Subcycle field waveforms are not unusual in terahertz technologies 8 , where such waveforms are generated as a result of optical rectification 9,10 , providing means for time-domain spectroscopy 11 , terahertz sensing 12 , and sub-quarter-cycle engineering 13. Terahertz field cycles are, clearly, too long to be relevant as probes for ultrafast dynamics in molecules, let alone the attosecond dynamics of electron wave packets and electron excitations in atoms and solids. Yet, the significance of the early work on subcycle terahertz field transients 8,9,14 is hard to overestimate-we owe it much of our understanding of fundamental properties of subcycle pulses and the universal tendencies in their unusual propagation dynamics. Optical methods of subcycle pulse generation rely on coherent field waveform synthesis 2 operating with high-order harmonics 15 , multiple Raman sidebands 16-19 , frequency-shifted supercontinua from hollow-core fibers 1,6 , and cascaded parametric amplification 20. As a promising alternative, anomalous-dispersion-assisted multioctave supercontinuum generation in solid materials 21 and guided-wave soliton self-compression (SSC) 22,23 can help create efficient sources of subcycle pulses covering a broad range of frequencies and peak powers. Here, we identify an unusual regime of ultrafast nonlinear dynamics in which an optical shock wave couples to soliton self-compression, steepening the tail of the pulse, thus yielding self-compressing soliton transients as short as the field sub-half-cycle. Optical shock waves are inevitable when the pulse duration of a field waveform approaches the field cycle 24. As their archetypical signature, optical shock waves tend to steepen the tail of the pulse, blue-shifting its spectrum 25. In special regimes of three-dimensional free-beam propagation, optical shock waves have been shown to force field waveforms to self-compress to subcycle pulse widths 26. Ordinarily, however, when building up via waveguide short-pulse evolution, optical shock waves do not lead to pulse shortening as a whole, giving rise to pulses with sharper trailing edges and asymmetric supercontinua. Still, our analysis presented in this paper shows that, when coupled to soliton self-compression an optical shock facilitates the generation of extraordinarily short field...

Scaling of self-compression of near-IR femtosecond pulses in hollow-core fibers down to the single-cycle limit

“…The process of self-compression is limited by soliton fission, where the dynamic balance between the various factors leads to the self-compression of these pulses [54,55]. Therefore, we investigate the dynamics of soliton fission for different gas pressures to gain insights.…”

High-peak-power mid-infrared OPCPAs for extreme nonlinear photonics

“…where ∆t F W HM is the pulse duration of the pulses at λ c , λ c is the centre frequency of the ultrafast pulses, and c is the speed of light in vacuum. While the number of optical cycles of a propagating electric field is required to be more than oneoptical-cycle, the above definition enables the generation of soliton transients with sub-cycle durations [68,120]. This section demonstrates the generation of nearsingle-cycle pulses via soliton self-compression in a novel ARR-PCF.…”

“…The pulse duration dependency in Argon pressure of the 3.2 µm SPM has been shown in Figure 3.13. While outside of the gas-cell, the FWHM duration of the mid-infrared pulses is limited to the single-cycle duration regime, the simulations carried out by our collaborators from MPL, estimated 3.2 µm pulse durations inside the ARR-PCF down to 3.5 fs [68,120]. The simulations show extreme ultrafast nonlinear dynamics where an optical-shock-wave couples with the soliton, steepening the tail of the pulse so strongly that soliton transients with optical cycles at FWHM down to 0.32 are generated (see Figure 2 (c) in [68]).…”