In this Letter, we show theoretically that the nonlinear photoionisation process of a noble gas inside a hollow-core photonic crystal fibre can be exploited in obtaining broadband supercontinuum generation via pumping close to the mid-infrared regime. The interplay between the Kerr and photoionisation nonlinearities is strongly enhanced in this regime. Photoionisation continuously modifies the medium dispersion, in which the refractive index starts to significantly decrease and approach the epsilon-near-zero regime. Subsequently, the self-phase modulation induced by the Kerr effect is boosted because of the accompanied slow-light effect. As a result of this interplay, an output spectrum that comprises of a broadband light with multiple dispersive-wave emission is obtained.
We present the use of linearly down-tapered gas-filled hollow-core photonic crystal fiber in a single-stage, pumped with pulses from a compact infrared laser source, to generate a supercontinuum carrying significant spectral power in the deep ultraviolet (200 - 300 nm). The generated supercontinuum extends from the near infrared down to around 213 nm with up to 0.83 mW/nm in the deep ultraviolet.
We demonstrate a route to supercontinuum generation in gas-filled hollow-core anti-resonant fibers through the creation of a broad vibrational Raman frequency comb followed by continuous broadening and merging of the comb lines through either rotational Raman scattering or the optical Kerr effect. Our demonstration experiments, utilizing a single pump pulse with 20 ps duration at 532 nm in a nitrogen-filled fiber, produce a supercontinuum spanning from 440 nm to 1200 nm, with an additional deep ultraviolet continuum from 250 nm to 360 nm. Numerical results suggest that this approach can produc…
Strong mid-infrared light-matter interaction has attracted extensive attention as it opens up new frontiers in nonlinear optics. Here we observe through simulations a novel aspect of mid-infrared pulse dynamics in a high-pressure gas-filled capillary, where a pulse with a power well below the critical power for Kerr self-focusing undergoes an astonishing rise of the peak intensity following an extremely efficient spectral broadening. This intensity enhancement is attributed to the Kerr-induced focusing of the supercontinuum. Our study provides an interesting perspective for controlling the las…
We report on the generation of a three-octave-wide supercontinuum extending from the vacuum ultraviolet (VUV) to the near-infrared, spanning at least 113 to 1000 nm (i.e., 11 to 1.2 eV), in He-filled hollow-core kagome-style photonic crystal fiber. Numerical simulations confirm that the main mechanism is a novel and previously undiscovered interaction between dispersive-wave emission and plasma-induced blueshifted soliton recompression around the fiber zero dispersion frequency. The VUV part of the supercontinuum, which modeling shows to be coherent and possess a simple phase structure, has su…
Although supercontinuum sources are readily available for the visible and near infrared, 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 (DUV) 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 kagomé-style hollow-core photonic crystal fiber (kagomé-PCF). Few-μJ, 30 fs pump…
Ultrafast broadband ultraviolet radiation is of importance in spectroscopy and photochemistry, since high photon energies enable single-photon excitations and ultrashort pulses allow time-resolved studies. Here we report the use of gas-filled hollow-core photonic crystal fibers (HC-PCFs) for efficient ultrafast nonlinear optics in the ultraviolet. Soliton self-compression of 400 nm pulses of (unprecedentedly low) ~500 nJ energies down to sub-6-fs durations is achieved, as well as resonant emission of tunable dispersive waves from these solitons. In addition, we discuss the generation of a flat…
Deep-UV (DUV) supercontinuum (SC) sources based on gas-filled hollow-core fibers constitute perhaps the most viable solution towards ultrafast, compact, and tunable lasers in the UV spectral region. Noise and spectral stability of such broadband sources are key parameters that define their true potential and suitability towards real-world applications. In order to investigate the spectral stability and noise levels in these fiber-based DUV sources, we generate an SC spectrum that extends from 180 nm (through phase-matched dispersive waves - DWs) to 4 μm by pumping an argon-filled hollow-core a…
Supercontinuum (SC) generation based on ultrashort pulse compression constitutes one of the most promising technologies towards an ultra-wide bandwidth, high-brightness and spatially coherent light sources for applications such as spectroscopy and microscopy. Here, multi-octave SC generation in a gas-filled hollow-core antiresonant fiber (HC-ARF) is reported spanning from 200 nm in the deep ultraviolet (DUV) to 4000 nm in the mid-infrared (mid-IR). A measured average output power of 5 mW was obtained by pumping at the center wavelength of the first anti-resonance transmission window (2460 nm) …
Ultrafast supercontinuum generation in gas-filled waveguides is one enabling technology for many intriguing application ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. Here we show that the structural resonances in gas-filled anti-resonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, allowing for the generation of more than three octaves of broadband light ranging deep UV wavelength towards the near infrared.Our observation relies o…
Gas-filled hollow-core photonic crystal fibre (PCF) is being used to generate ever wider supercontinuum spectra, in particular via dispersive wave (DW) emission in the deep and vacuum ultraviolet, with a multitude of applications. DWs are the result of the resonant transfer of energy from a self-compressed soliton, a process which relies crucially on phase matching. It was recently predicted that, in the strong-field regime, the additional transient anomalous dispersion introduced by gas ionization would allow phase-matched DW generation in the mid-infrared (MIR)-something that is forbidden in…
We theoretically study a novel approach for soliton-induced high-power supercontinuum generation by using kagome lattice HC-PCFs filled with a noble gas. Anomalous dispersion and broad-band low loss of these fibers enable the generation of two-octave broad spectra by fs pulses, with high coherence and high spectral peak power densities up to five orders of magnitude larger than in standard PCFs. In addition, up to 20 percents of the output radiation energy forms a narrow UV/VUV band, which can be tuned by contolling the pressure in the range from 350 nm to 120 nm. In the temporal domain this c…
We report on the generation of intense extreme ultraviolet (EUV) supercontinuum with photon energies spanning from 35 eV to 50 eV (i. e., supporting an isolated attosecond pulse with a duration of ~271 as) by loosely focusing 35 fs, 11 mJ pulses from a femtosecond laser amplifier into a 10-mm long gas cell filled with krypton gas. The dramatic change of spectral and temporal properties of the driver pulses after passing through the gas cell indicates that propagation effects play a significant role in promoting the generation of the EUV supercontinuum.
We study theoretically the propagation of relatively long pulses with ionizing intensities in a hollow-core photonic crystal fiber filled with a Raman-inactive gas. Due to photoionization, previously unknown types of asymmetric self-phase modulation and `universal' modulational instabilities existing in both normal and anomalous dispersion regions appear. We also show that it is possible to spontaneously generate a plasma-induced continuum of blueshifting solitons, opening up new possibilities for pushing supercontinuum generation towards shorter and shorter wavelengths.
We demonstrate efficient generation of coherent super-octave pulses via a single-stage spectral broadening of a Yb:KGW laser in a single, pressurized, Ne-filled, hollow-core fiber capillary. Emerging pulses spectrally spanning over more than $\sim$1 PHz (250 nm- 1600 nm) at a dynamic range of $\sim$60 dB, and an excellent beam quality open the door to combining Yb:KGW lasers with modern light field synthesis techniques. Compression of a fraction of the generated supercontinuum to intense (8 fs, $\sim$2.4 cycle, $\sim$650 $μ$J) pulses allows convenient use of these novel laser sources in strong…
We report generation of an ultrafast supercontinuum extending into the mid- infrared in gas-filled single-ring hollow-core photonic crystal fiber (SR-PCF) pumped by 1.7 $μ$m light from an optical parametric amplifier. The simple fiber structure offers shallow dispersion and flat transmission in the near and mid-infrared, enabling the generation of broadband spectra extending from 300 nm to 3.1 $μ$m, with a total energy of a few $μ$J. In addition, we report the emission of ultraviolet dispersive waves whose frequency can be tuned simply by adjusting the pump wavelength. SR-PCF also provides an …
The physics and applications of fiber-based supercontinuum (SC) sources have been a subject of intense interest over the last decade, with significant impact on both basic science and industry. New uses for SC sources are also constantly emerging due to their unique properties that combine high brightness, multi-octave frequency bandwidth, fiber delivery, and single-mode output. The last few years have seen significant research efforts focused on extending the wavelength coverage of SC sources towards the 2 to 20 $μ$m molecular fingerprint mid-infrared (MIR) region and in the ultraviolet (UV) …
The field of attosecond science was first enabled by nonlinear compression of intense laser pulses to a duration below two optical cycles. Twenty years later, creating such short pulses still requires state-of-the-art few-cycle laser amplifiers to most efficiently exploit 'instantaneous' optical nonlinearities in noble gases for spectral broadening and parametric frequency conversion. Here, we show that nonlinear compression can in fact be much more efficient when driven in molecular gases by pulses substantially longer than a few cycles, due to enhanced optical nonlinearity associated with ro…
We investigate numerically soliton-plasma interaction in a noble-gas-filled silica hollow-core anti-resonant fiber pumped in the mid-IR at 3.0 μm. We observe multiple soliton self-compression stages due to distinct stages where either the self-focusing or the self-defocusing nonlinearity dominates. Specifically, the parameters may be tuned so the competing plasma self-defocusing nonlinearity only dominates over the Kerr self-focusing nonlinearity around the soliton self-compression stage, where the increasing peak intensity on the leading pulse edge initiates a competing self-defocusing plasma…
Vibrational ultrastrong coupling (USC), where the light-matter coupling strength is comparable to the vibrational frequency of molecules, presents new opportunities to probe the interactions of molecules with zero-point fluctuations, harness cavity-enhanced chemical reactions, and develop novel devices in the mid-infrared regime. Here we use epsilon-near-zero nanocavities filled with a model polar medium (SiO$_2$) to demonstrate USC between phonons and gap plasmons. We present classical and quantum mechanical models to quantitatively describe the observed plasmon-phonon USC phenomena and demon…
We report generation of a femtosecond supercontinuum extending from the ultraviolet to the near-infrared and detection of its carrier-envelope phase variation by f-to-2f interferometry. The spectrum is generated in a gas-filled hollow-core photonic crystal fiber where soliton dynamics allows CEP-stable self-compression of OPCPA pump pulses at 800 nm to a duration of 1.7 optical cycles, followed by dispersive wave emission. The source provides up to 1 μJ of pulse energy at 800 kHz repetition rate resulting in 0.8 W of average power, and can be extremely useful for example in strong-field physic…
We report a novel technique for launching broadband laser light into liquid-filled hollow-core photonic crystal fiber (HC-PCF). It uniquely offers self-alignment and self-stabilization via optomechanical trapping of a fused silica nanospike, fabricated by thermally tapering and chemically etching a single mode fiber into a tip diameter of 350 nm. We show that a trapping laser, delivering ~300 mW at 1064 nm, can be used to optically align and stably maintain the nanospike at the core center. Once this is done, a broadband supercontinuum beam (~575 to 1064 nm) can be efficiently and close to ach…
The effective Kerr nonlinearity of hollow-core kagome-style photonic crystal fiber (PCF) filled with argon gas increases over 100 times when the pressure is increased from 1 to 150 bar, reaching 15 % of that of bulk silica glass, while the zero dispersion wavelength shifts from 300 to 900 nm. The group velocity dispersion of the system is uniquely pressure-tunable over a wide range while avoiding Raman scattering : absent in noble gases and having an extremely high optical damage threshold. As a result, detailed and well controlled studies of nonlinear effects can be performed, in both normal …
We propose a new approach to near-infrared molecular spectroscopy, harnessing advanced concepts of optical telecommunications and supercontinuum photonics. We generate, without mode-locked lasers, two frequency combs of slightly different repetition frequencies and moderate, but rapidly tunable, spectral span. The output of a frequency-agile continuous wave laser is split and sent into two electro-optic intensity modulators. Flat-top low-noise frequency combs are produced by wave-breaking in a nonlinear optical fiber of normal dispersion. With a dual-comb spectrometer, we record Doppler-limite…
