Optical soliton dynamics in a waveguide can cause the extreme alteration of the temporal and spectral shape of a propagating light pulse. They occur at watt to kilowatt peak power in glass-core optical fibres and up to the gigawatt level in gas-filled microstructured hollow-core fibres. Here we demonstrate, for the first time, optical soliton dynamics in conventional large-core hollow capillary fibres. Our analysis and modelling show that this enables further scaling of soliton effects by several orders of magnitude to the multi-mJ energy and terawatt peak power level. We experimentally demonstrate two key soliton effects. First, we observe self-compression to sub-cycle pulses and infer the creation of sub-femtosecond field waveforms-a route to high-power optical attosecond pulse generation. Second, we efficiently generate continuously tunable high-energy (1-13 µJ) pulses in the vacuum and deep ultraviolet spectral region (110 nm to 400 nm) through resonant dispersive-wave emission. This new regime of high-energy ultrafast soliton effects promises to be the foundation of a new generation of table-top light sources for ultrafast strong-field physics and advanced spectroscopy. * j.travers@hw.ac.uk; http://lupo-lab.com arXiv:1811.05877v1 [physics.optics]

Although supercontinuum sources are readily available for the visible and near infrared (IR), and recently also for the mid-IR, many areas of biology, chemistry, and physics would benefit greatly from the availability of compact, stable, and spectrally bright deep-ultraviolet and vacuum-ultraviolet (VUV) supercontinuum sources. Such sources have, however, not yet been developed. Here we report the generation of a bright supercontinuum, spanning more than three octaves from 124 nm to beyond 1200 nm, in hydrogen-filled kagome-style hollow-core photonic crystal fiber (kagome-PCF). Few-microjoule, 30 fs pump pulses at wavelength of 805 nm are launched into the fiber, where they undergo self-compression via the Raman-enhanced Kerr effect. Modeling indicates that before reaching a minimum subcycle pulse duration of similar to 1 fs, much less than one period of molecular vibration (8 fs), nonlinear reshaping of the pulse envelope, accentuated by self-steepening and shock formation, creates an ultrashort feature that causes impulsive excitation of long-lived coherent molecular vibrations. These phase modulate a strong VUV dispersive wave (at 182 nm or 6.8 eV) on the trailing edge of the pulse, further broadening the spectrum into the VUV. The results also show for the first time that kagome-PCF guides well in the VUV. (C) 2015 Optical Society of Americ

Raman effect in gases can generate an extremely long-living wave of coherence that can lead to the establishment of an almost perfect temporal periodic variation of the medium refractive index. We show theoretically and numerically that the equations, regulate the pulse propagation in hollow-core photonic crystal fibers filled by Raman-active gas, are exactly identical to a classical problem in quantum condensed matter physics - but with the role of space and time reversed - namely an electron in a periodic potential subject to a constant electric field. We are therefore able to infer the existence of Wannier-Stark ladders, Bloch oscillations, and Zener tunneling, phenomena that are normally associated with condensed matter physics, using purely optical means.

Infrared femtosecond laser pulses are important tools both in strong-field physics, driving x-ray high-harmonic generation, and as the basis for widely tunable, if inefficient, ultrafast sources in the visible and ultraviolet. Although anomalous material dispersion simplifies compression to few-cycle pulses, attosecond pulses in the infrared have remained out of reach. We demonstrate soliton self-compression of 1800-nm laser pulses in hollow capillary fibers to subcycle envelope duration (2 fs) with 27-GW peak power, corresponding to attosecond field transients. In the same system, we generate wavelength-tunable few-femtosecond pulses from the ultraviolet (300 nm) to the infrared (740 nm) with energy up to 25 μJ and efficiency up to 12%, and experimentally characterize the generation dynamics in the time-frequency domain. A compact second stage generates multimicrojoule pulses from 210 to 700 nm using less than 200 μJ of input energy. Our results significantly expand the toolkit available to ultrafast science.

We demonstrate high-energy resonant dispersivewave emission in the deep ultraviolet (218 to 375 nm) from optical solitons in short (15 to 34 cm) hollow capillary fibres. This down-scaling in length compared to previous results in capillaries is achieved by using small core diameters (100 and 150 µm) and pumping with 6.3 fs pulses at 800 nm. We generate pulses with energies of 4 to 6 µJ across the deep ultraviolet in a 100 µm capillary and up to 11 µJ in a 150 µm capillary. From comparisons to simulations we estimate the ultraviolet pulse to be 2 to 2.5 fs in duration. We also numerically study the influence of pump duration on the bandwidth of the dispersive wave. Optical soliton dynamics, obtained by balancing linear and nonlinear contributions to the phase of a propagating light pulse, are a key phenomenon in nonlinear fibre optics. Resonant dispersive wave (RDW) emission in gas-filled hollow fibres is a particularly promising application of this effect, enabling the generation of tuneable ultrashort pulses and supercontinua at shorter wavelengths than possible in any solid-core waveguide [1,2,3,4,5], from the vacuum ultraviolet to the visible spectral region. These dynamics were pioneered in hollow-core photonic-crystal fibres (HC-PCF). Recently, we demonstrated that they can be scaled in energy by up to several orders of magnitude in simple hollow capillary fibres (HCF) [5]. Pumping gas-filled large-core HCF with 10 fs pulses enabled soliton self-compression to 1 fs in the near infrared-an optical attosecond pulse-and the generation of few-femtosecond vacuum and deep ultraviolet (VUV/DUV) pulses at unprecedented peak power, comparable to free-electron lasers. We also showed that up-scaling of those dynamics to the terrawatt scale is feasible by further increasing the HCF core size. Here, we down-scale the core size instead to achieve a more compact and practical setup. Whereas our first demonstration made use of 3 m HCF, here we show that this can be reduced to just 15 to 34 cm when using small-core HCF and even shorter pump pulses-6.3 fs, as readily generated in widely used conventional HCF pulse compression systems. The required pulse energy is also reduced, which is an additional advantage if multiple frequency conversion schemes are to be driven simultaneously, as for instance in multi-colour time-resolved spectroscopy experiments.The HCF length required to generate a dispersive wave is primarily determined by the distance over which soliton selfcompression occurs. This is well approximated by the fission length L f ,where N is the soliton order and L d and L nl are the dispersion and nonlinear lengths, describing the length scales of groupvelocity dispersion (GVD) and self-phase modulation (SPM), respectively [6]. Broadly similar soliton dynamics and RDW emission can be obtained with different parameters, provided that the soliton order and the zero-dispersion wavelength λ zd remain the same. In particular, the spectral location of RDW emission is chiefly determined by the pump wavelength λ0 and λ zd . W...