Dr. Francesco Tani

Temporal Self-Compression and Self-Frequency Shift of Submicrojoule Pulses at a Repetition Rate of 8 MHz

Francesco Tani, Jacob Lampen, Martin Butryn, Michael Frosz, Jie Jiang, Martin E. Fermann, Philip Russell

We combine soliton dynamics in gas-filled hollow-core photonic crystal fibers with a state-of-the-art fiber laser to realize a turnkey system producing few-femtosecond pulses at 8-MHz repetition rate at pump energies as low as 220 nJ. Furthermore, by exploiting the soliton self-frequency shift in a second hydrogen-filled hollow-core fiber, we efficiently generate pulses as short as 22 fs, continuously tunable from 1100 to 1474 nm.

Scaling rules for high quality soliton self-compression in hollow-core fibers

Daniel Schade, Felix Köttig, Johannes Köhler, Michael H. Frosz, Philip St.J. Russell, Francesco Tani

Soliton dynamics can be used to temporally compress laser pulses to few fs durations in many different spectral regions. Here we study analytically, numerically and experimentally the scaling of soliton dynamics in noble gas-filled hollow-core fibers. We identify an optimal parameter region, taking account of higher-order dispersion, photoionization, self-focusing, and modulational instability. Although for single-shots the effects of photoionization can be reduced by using lighter noble gases, they become increasingly important as the repetition rate rises. For the same optical nonlinearity, the higher pressure and longer diffusion times of the lighter gases can considerably enhance the long-term effects of ionization, as a result of pulse-by-pulse buildup of refractive index changes. To illustrate the counter-intuitive nature of these predictions, we compressed 250 fs pulses at 1030 nm in an 80-cm-long hollow-core photonic crystal fiber (core radius 15 µm) to ∼5 fs duration in argon and neon, and found that, although neon performed better at a repetition rate of 1 MHz, stable compression in argon was still possible up to 10 MHz.

Seven-octave high-brightness and carrier-envelope-phase-stable light source

Ugaitz Elu, Luke Maidment, Lenard Vamos, Francesco Tani, David Novoa, Michael H. Frosz, Valeriy Badikov, Dmitrii Badikov, Valentin Petrov, et al.

High-brightness sources of coherent and few-cycle-duration light waveforms with spectral coverage from the ultraviolet to the terahertz would offer unprecedented versatility and opportunities for a wide range of applications from bio-chemical sensing1 to time-resolved and nonlinear spectroscopy, and to attosecond light-wave electronics. Combinations of various sources with frequency conversion and supercontinuum generation can provide relatively large spectral coverage, but many applications require a much broader spectral range and low-jitter synchronization for time-domain measurements. Here, we present a carrier-envelope-phase (CEP)-stable light source, seeded by a mid-infrared frequency comb, with simultaneous spectral coverage across seven optical octaves, from the ultraviolet (340 nm) into the terahertz (40,000 nm). Combining soliton self-compression and dispersive wave generation in an anti-resonant-reflection photonic-crystal fibre with intra-pulse difference frequency generation in BaGa2GeSe6, the spectral brightness is two to five orders of magnitude above that of synchrotron sources. This will enable high-dynamic-range spectroscopies and provide numerous opportunities in attosecond physics and material sciences.

Covariance spectroscopy of molecular gases using fs pulse bursts created by modulational instability in gas-filled hollow-core fiber

Mallika Irene Suresh, Philip Russell, Francesco Tani

We present a technique that uses noisy broadband pulse bursts generated by modulational instability to probe nonlinear processes, including infrared-inactive Raman transitions, in molecular gases. These processes imprint correlations between different regions of the noisy spectrum, which can be detected by acquiring single shot spectra and calculating the Pearson correlation coefficient between the different frequency components. Numerical simulations verify the experimental measurements and are used to further understand the system and discuss methods to improve the signal strength and the spectral resolution of the technique.

Modulational-instability-free pulse compression in anti-resonant hollow-core photonic crystal fiber

Felix Köttig, Francesco Tani, Philip Russell

Gas-filled hollow-core photonic crystal fiber (PCF) is used for efficient nonlinear temporal compression of femtosecond laser pulses, two main schemes being direct soliton-effect self-compression and spectral broadening followed by phase compensation. To obtain stable compressed pulses, it is crucial to avoid decoherence through modulational instability (MI) during spectral broadening. Here, we show that changes in dispersion due to spectral anti-crossings between the fundamental-core mode and core wall resonances in anti-resonant-guiding hollow-core PCF can strongly alter the MI gain spectrum, enabling MI-free pulse compression for optimized fiber designs. The results are important, since MI cannot always be suppressed by pumping in the normal dispersion regime.

Efficient single-cycle pulse compression of an ytterbium fiber laser at 10 MHz repetition rate

Felix Köttig, Daniel Schade, Johannes Köhler, Philip Russell, Francesco Tani

Over the past years, ultrafast lasers with average powers in the 100 W range have become a mature technology, with a multitude of applications in science and technology. Nonlinear temporal compression of these lasers to few- or even single-cycle duration is often essential, yet still hard to achieve, in particular at high repetition rates. Here we report a two-stage system for compressing pulses from a 1030 nm ytterbium fiber laser to single-cycle durations with 5 µJ output pulse energy at 9.6 MHz repetition rate. In the first stage, the laser pulses are compressed from 340 to 25 fs by spectral broadening in a krypton-filled single-ring photonic crystal fiber (SR-PCF), subsequent phase compensation being achieved with chirped mirrors. In the second stage, the pulses are further compressed to single-cycle duration by soliton-effect self-compression in a neon-filled SR-PCF. We estimate a pulse duration of ∼3.4 fs at the fiber output by numerically back-propagating the measured pulses. Finally, we directly measured a pulse duration of 3.8 fs (1.25 optical cycles) after compensating (using chirped mirrors) the dispersion introduced by the optical elements after the fiber, more than 50% of the total pulse energy being in the main peak. The system can produce compressed pulses with peak powers >0.6 GW and a total transmission exceeding 66%.

Pump-Probe Study of Plasma Dynamics in Gas-Filled Photonic Crystal Fiber Using Counterpropagating Solitons

Mallika Irene Suresh, Felix Köttig, Johannes Köhler, Francesco Tani, Philip Russell

We present a pump-probe technique for monitoring ultrafast polarizability changes. In particular, we use it to measure the plasma density created at the temporal focus of a self-compressing higher-order pump soliton in a gas-filled hollow-core photonic crystal fiber. This is done by monitoring the wavelength of the dispersive wave emission from a counterpropagating probe soliton. By varying the relative delay between pump and probe, the plasma density distribution along the fiber can be mapped out. Compared with recently introduced interferometric side probing for monitoring the plasma density, our technique is relatively immune to instabilities caused by air turbulence and mechanical vibration. The results of two experiments on argon- and krypton-filled fiber are presented and compared to numerical simulations. The technique provides an important tool for probing photoionization in many different gases and gas mixtures, as well as ultrafast changes in dispersion in many other contexts.

Carrier-envelope-phase-stable soliton-based pulse compression to 4.4  fs and ultraviolet generation at the 800  kHz repetition rate

Alexey Ermolov, Christian Heide, Philip Dienstbier, Felix Köttig, Francesco Tani, Peter Hommelhoff, Philip Russell

In this Letter, we report the generation of a femtosecond supercontinuum extending from the ultraviolet to the near-infrared spectrum and detection of its carrier-envelope-phase (CEP) variation by f-to-2f interferometry. The spectrum is generated in a gas-filled hollow-core photonic crystal fiber, where soliton dynamics allows the CEP-stable self-compression of the optical parametric chirped-pulse amplifier 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 the 800 kHz repetition rate, resulting in 0.8 W of average power, and it can be extremely useful, for example in strong-field physics, pump–probe measurements, and ultraviolet frequency comb metrology.

Generation of 1.5 cycle pulses at 780 nm at oscillator repetition rates with stable carrier-envelope phase

Philip Dienstbier, Francesco Tani, Takuya Higuchi, John Travers, Philip Russell, Peter Hommelhoff

We demonstrate a spectral broadening and compression setup for carrier-envelope phase (CEP) stable sub-10-fs Ti:sapphire oscillator pulses resulting in 3.9 fs pulses spectrally centered at 780 nm. Pulses from the oscillator with 2 nJ energy are launched into a 1 mm long all-normal dispersive solid-core photonic crystal fiber and spectrally broadened to more than one octave. Subsequent pulse compression is achieved with a phase-only 4f pulse shaper. Second harmonic frequency resolved optical gating with a ptychographic reconstruction algorithm is used to obtain the spectral phase, which is fed back as a phase mask to the shaper display for pulse compression. The compressed pulses are CEP stable with a long term standard deviation of 0.23 rad for the CEP noise and 0.32 rad for the integrated rms phase jitter. The high total throughput of 15% results in a remaining pulse energy of about 300 pJ at 80 MHz repetition rate. With these parameters and the ability to tailor the spectral phase, the system is well suited for waveform sensitive photoemission experiments with needle tips or nanostructures and can be easily adapted to other sub-10 fs ultra-broadband Ti:sapphire oscillators.

Fabrication and non-destructive characterization of tapered single-ring hollow-core photonic crystal fiber

Riccardo Pennetta, Michael T. Enders, Michael H. Frosz, Francesco Tani, Philip St. J. Russell

We report on the properties of tapered single-ring hollow-core photonic-crystal fibers, with a particular emphasis on applications in nonlinear optics. The simplicity of these structures allows the use of non-invasive side-illumination to assess the quality of the tapering process, by<br>observing the scattered far-field spectrum originating from excitation of whispering-gallery modes in the cladding capillaries. We investigate the conditions that ensure adiabatic propagation in the up- and down-tapers, and the scaling of loss-bands (created by anti-crossings between the core mode and modes in the capillary walls) with taper ratio. We also present an analytical model for the pressure profile along a tapered hollow fiber under differential pumping

Spatio-temporal measurement of ionization-induced modal index changes in gas-filled PCF by prism-assisted side-coupling

Barbara M. Trabold, Mallika I. Suresh, Johannes R. Köhler, Michael H. Frosz, Francesco Tani, Philip St. J. Russell

We report the use of prism-assisted side-coupling to investigate the spatio-temporal dynamics of photoionization in an Ar-filled hollow-core photonic crystal fiber. By launching four different LP core modes we are able to probe temporal and spatial changes in the modal refractive index on timescales from a few hundred picoseconds to several hundred microseconds after the ionization event. We experimentally analyze the underlying gas density waves and find good agreement with quantitative and qualitative hydrodynamic predictions. Moreover, we observe periodic modulations in the MHz-range lasting for a few microseconds, indicating nanometer-scale vibrations of the fiber structure, driven by gas density waves.

Direct characterization of tuneable few-femtosecond dispersive-wave pulses in the deep UV

Christian Brahms, Dane R. Austin, Francesco Tani, Allan S. Johnson, Douglas Garratt, John. C. Travers, John W. G. Tisch, Philip Russell, Jon P. Marangos

Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherentand broadband radiation, but so far the generation of fewfemtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterize tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.

Long-Lived Refractive-Index Changes Induced by Femtosecond Ionization in Gas-Filled Single-Ring Photonic-Crystal Fibers

Johannes R. Koehler, Felix Köttig, Barbara M. Trabold, Francesco Tani, Philip St. J. Russell

We investigate refractive-index changes caused by femtosecond photoionization in a gas-filled hollow-core photonic-crystal fiber. Using spatially-resolved interferometric side-probing, we find that these changes live for tens of microseconds after the photoionization event — eight orders of magnitude longer than the pulse duration. Oscillations in the megahertz frequency range are simultaneously observed, caused by mechanical vibrations of the thin-walled capillaries surrounding the hollow core. These two nonlocal effects can affect the propagation of a second pulse that arrives within their lifetime, which works out to repetition rates of tens of kilohertz. Filling the fiber with an atomically lighter gas significantly reduces ionization, lessening the strength of the refractive-index changes. The results will be important for understanding the dynamics of gas-based fiber systems operating at high intensities and high repetition rates, when temporally nonlocal interactions between successive laser pulses become relevant.

Broadband and tunable time-resolved THz system using argon-filled hollow-core photonic crystal fiber

Wei Cui, Aidan W. Schiff-Kearn, Emily Zhang, Nicolas Couture, Francesco Tani, David Novoa, Philip St. J. Russell, Jean-Michel Ménard

We demonstrate broadband, frequency-tunable, phase-locked terahertz (THz) generation and detection based on difference frequency mixing of temporally and spectrally structured near-infrared (NIR) pulses. The pulses are prepared in a gas-filled hollow-core<br>photonic crystal fiber (HC-PCF), whose linear and nonlinear optical properties can be adjusted by tuning the gas pressure. This permits optimization of both the spectral broadening of the pulses due to self-phase modulation (SPM) and the generated THz spectrum. The properties of the prepared pulses, measured at several different argon gas pressures, agree well with the results of numerical modeling. Using these pulses, we perform difference frequency generation in a standard time-resolved THz scheme. As the argon pressure is gradually increased from 0 to 10 bar, the NIR pulses spectrally broaden from 3.5 to 8.7 THz, while the measured THz bandwidth increases correspondingly from 2.3 to 4.5 THz. At 10 bar, the THz spectrum extends to 6 THz, limited only by the spectral bandwidth of our time-resolved detection scheme. Interestingly, SPM in the HC-PCF produces asymmetric spectral broadening that may be used to enhance the generation of selected THz frequencies. This scheme, based on a HC-PCF pulse shaper, holds great promise for broadband time-domain spectroscopy in the THz, enabling the use of compact and stable ultrafast laser sources with relatively narrow linewidths (<4 THz).

UV Soliton Dynamics and Raman-Enhanced Supercontinuum Generation in Photonic Crystal Fiber

Pooria Hosseini, Alexey Ermolov, Francesco Tani, David Novoa, Philip Russell

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 selfcompression 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 supercontinuum extending from the deep ultraviolet to the visible in a hydrogen-filled HC-PCF. Comparisons with argon-filled fibers show that the enhanced Raman gain at high frequencies makes the hydrogen system more efficient. As HC-PCF technology develops, we expect these fiber-based ultraviolet sources to lead to new applications.

Effect of anti-crossings with cladding resonances on ultrafast nonlinear dynamics in gas-filled photonic crystal fibers

Francesco Tani, Felix Köttig, David Novoa, Ralf Keding, Philip Russell

Spectral anti-crossings between the fundamental guided mode and core-wall resonances alter the dispersion in hollow-core anti-resonant-reflection photonic crystal fibers. Here we study the effect of this dispersion change on the nonlinear propagation and dynamics of ultrashort pulses. We find that it causes emission of narrow spectral peaks through a combination of four-wave mixing and dispersive wave emission. We further investigate the influence of the anti-crossings on nonlinear pulse propagation and show that their impact can be minimized by adjusting the core-wall thickness in such a way that the anti-crossings lie spectrally distant from the pump wavelength.

Generation of microjoule pulses in the deep ultraviolet at megahertz repetition rates

Felix Koettig, Francesco Tani, Christian Martens-Biersach, John C. Travers, Philip St J. Russell

Although ultraviolet (UV) light is important in many areas of science and technology, there are very few if any lasers capable of delivering wavelength-tunable ultrashort UV pulses at high repetition rates. Here we report the generation of deep UV laser pulses at megahertz repetition rates and microjoule energies by means of dispersive wave (DW) emission from self-compressed solitons in gas-filled single-ring hollow-core photonic crystal fiber (SR-PCF). Pulses from an ytterbium fiber laser (similar to 300 fs) are first compressed to <25 fs in a SR-PCF-based nonlinear compression stage and subsequently used to pump a second SR-PCF stage for broadband DW generation in the deep UV. The UV wavelength is tunable by selecting the gas species and the pressure. Through rigorous optimization of the system, in particular employing a large-core fiber filled with light noble gases, we achieve 1 mu J pulse energies in the deep UV, which is more than 10 times higher, at average powers more than four orders of magnitude greater (reaching 1 W) than previously demonstrated, with only 20 mu J pulses from the pump laser. (C) 2017 Optical Society of America

Continuously wavelength-tunable high harmonic generation via soliton dynamics

Francesco Tani, Michael H. Frosz, John C. Travers, Philip St. J. Russell

We report the generation of high harmonics in a gas jet pumped by pulses self-compressed in a He-filled hollow-core photonic crystal fiber through the soliton effect. The gas jet is placed directly at the fiber output. As the energy increases, the ionization-induced soliton blueshift is transferred to the high harmonics, leading to emission bands that are continuously tunable from 17 to 45 eV. (C) 2017 Optical Society of America

Mid-infrared dispersive wave generation in gas-filled photonic crystal fibre by transient ionization-driven changes in dispersion

F. Koettig, D. Novoa, F. Tani, M. C. Guenendi, M. Cassataro, J. C. Travers, P. St. J. Russell

Gas-filled hollow-core photonic crystal fibre is being used to generate ever wider super-continuum spectra, in particular via dispersive wave emission in the deep and vacuum ultraviolet, with a multitude of applications. Dispersive waves are the result of nonlinear transfer of energy from a self-compressed soliton, a process that 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 dispersive wave generation in the mid-infrared-something that is forbidden in the absence of free electrons. Here we report the experimental observation of such mid-infrared dispersive waves, embedded in a 4.7-octave-wide supercontinuum that uniquely reaches simultaneously to the vacuum ultraviolet, with up to 1.7W of total average power.

PHz-Wide Spectral Interference Through Coherent Plasma-Induced Fission of Higher-Order Solitons

F. Koettig, F. Tani, J. C. Travers, P. St. J. Russell

We identify a novel regime of soliton-plasma interactions in which high-intensity ultrashort pulses of intermediate soliton order undergo coherent plasma-induced fission. Experimental results obtained in gas-filled hollow-core photonic crystal fiber are supported by rigorous numerical simulations. In the anomalous dispersion regime, the cumulative blueshift of higher-order input solitons with ionizing intensities results in pulse splitting before the ultimate self-compression point, leading to the generation of robust pulse pairs with PHz bandwidths. The novel dynamics closes the gap between plasma-induced adiabatic soliton compression and modulational instability.

High average power and single-cycle pulses from a mid-IR optical parametric chirped pulse amplifier

Ugaitz Elu, Matthias Baudisch, Hugo Pires, Francesco Tani, Michael H. Frosz, Felix Koettig, Alexey Ermolov, Philip St J. Russell, Jens Biegert

In attosecond and strong-field physics, the acquisition of data in an acceptable time demands the combination of high peak power with high average power. We report a 21 W mid-IR optical parametric chirped pulse amplifier (OPCPA) that generates 131 mu J and 97 fs (sub-9-cycle) pulses at a 160 kHz repetition rate and at a center wavelength of 3.25 mu m. Pulse-to-pulse stability of the carrier envelope phase (CEP)-stable output is excellent with a 0.33% rms over 288 million pulses (30 min) and compression close to a single optical cycle was achieved through soliton self-compression inside a gas-filled mid-IR antiresonant-guiding photonic crystal fiber. Without any additional compression device, stable generation of 14.5 fs (1.35-optical-cycle) pulses was achieved at an average power of 9.6 W. The resulting peak power of 3.9 GW in combination with the near-single-cycle duration and intrinsic CEP stability makes our OPCPA a key-enabling technology for the next generation of extreme photonics, strong-field attosecond research, and coherent x-ray science. (C) 2017 Optical Society of America

Extremely broadband single-shot cross-correlation frequency-resolved optical gating using a transient grating as gate and dispersive element

H. Valtna-Lukner, F. Belli, A. Ermolov, F. Koettig, K. F. Mak, F. Tani, J. C. Travers, P. St. J. Russell

Across-correlation frequency-resolved optical gating (FROG) concept, potentially suitable for characterizing few or sub-cycle pulses in a single shot, is described in which a counter-propagating transient grating is used as both the gate and the dispersive element in a FROG spectrometer. An all-reflective setup, which can operate over the whole transmission range of the nonlinear medium, within the sensitivity range of the matrix sensor, is also proposed, and proof-of-principle experiments for the ultraviolet and visible-to-near-infrared spectral ranges are reported. Published by AIP Publishing.

Generation of three-octave-spanning transient Raman comb in hydrogen-filled hollow-core PCF

F. Tani, F. Belli, A. Abdolvand, J. C. Travers, P. St. J. Russell

A noise-seeded transient comb of Raman sidebands spanning three octaves from 180 to 2400 nm, is generated by pumping a hydrogen-filled hollow-core photonic crystal fiber with 26-mu J, 300-fs pulses at 800 nm. The pump pulses are spectrally broadened by both Kerr and Raman-related self-phase modulation (SPM), and the broadening is then transferred to the Raman lines. In spite of the high intensity, and in contrast to bulk gas-cell based experiments, neither SPM broadening nor ionization are detrimental to comb formation. (C) 2015 Optical Society of America

As2S3-silica double-nanospike waveguide for mid-infrared supercontinuum generation

Shangran Xie, Francesco Tani, John C. Travers, Patrick Uebel, Celine Caillaud, Johann Troles, Markus A. Schmidt, Philip St J. Russell

A double-nanospike As2S3-silica hybrid waveguide structure is reported. The structure comprises nanotapers at input and output ends of a step-index waveguide with a subwavelength core (1 mu m in diameter), with the aim of increasing the in-coupling and out-coupling efficiency. The design of the input nanospike is numerically optimized to match both the diameter and divergence of the input beam, resulting in efficient excitation of the fundamental mode of the waveguide. The output nanospike is introduced to reduce the output beam divergence and the strong endface Fresnel reflection. The insertion loss of the waveguide is measured to be similar to 2 dB at 1550 nm in the case of free-space in-coupling, which is similar to 7 dB lower than the previously reported single-nanospike waveguide. By pumping a 3-mm-long waveguide at 1550 nm using a 60-fs fiber laser, an octave-spanning supercontinuum (from 0.8 to beyond 2.5 mu m) is generated at 38 pJ input energy. (C) 2014 Optical Society of America

Multimode ultrafast nonlinear optics in optical waveguides: numerical modeling and experiments in kagome photonic-crystal fiber

Francesco Tani, John C. Travers, Philip St. J. Russell

We introduce a general full-field propagation equation for optical waveguides, including both fundamental and higher order modes, and apply it to the investigation of spatial nonlinear effects of ultrafast and extremely broad-band nonlinear processes in hollow-core optical fibers. The model is used to describe pulse propagation in gas-filled hollow-core waveguides including the full dispersion, Kerr, and ionization effects. We study third-harmonic generation into higher order modes, soliton emission of resonant dispersive waves into higher order modes, intermodal four-wave mixing, and Kerr-driven transverse self-focusing and plasma-defocusing, all in a gas-filled kagome photonic crystal fiber system. In the latter case a form of waveguide-based filamentation is numerically predicted. (C) 2014 Optical Society of America

Low loss hollow optical-waveguide connection from atmospheric pressure to ultra-high vacuum

A. Ermolov, K. F. Mak, F. Tani, P. Hoelzer, J. C. Travers, P. St J. Russell

A technique for optically accessing ultra-high vacuum environments, via a photonic-crystal fiber with a long small hollow core, is described. The small core and the long bore enable a pressure ratio of over 10(8) to be maintained between two environments, while permitting efficient and unimpeded delivery of light, including ultrashort optical pulses. This delivery can be either passive or can encompass nonlinear optical processes such as optical pulse compression, deep UV generation, supercontinuum generation, or other useful phenomena. (C) 2013 AIP Publishing LLC.

PHz-wide Supercontinua of Nondispersing Subcycle Pulses Generated by Extreme Modulational Instability

F. Tani, J. C. Travers, P. St. J. Russell

Modulational instability (MI) of 500 fs, 5 mu J pulses, propagating in gas-filled hollow-core kagome photonic crystal fiber, is studied numerically and experimentally. By tuning the pressure and launched energy, we control the duration of the pulses emerging as a consequence of MI and hence are able to study two regimes: the classical MI case leading to few-cycle solitons of the nonlinear Schrodinger equation; and an extreme case leading to the formation of nondispersing subcycle pulses (0.5 to 2 fs) with peak intensities of order 10(14) Wcm(-2). Insight into the two regimes is obtained using a novel statistical analysis of the soliton parameters. Numerical simulations and experimental measurements show that, when a train of these pulses is generated, strong ionization of the gas occurs. This extreme MI is used to experimentally generate a high energy (> 1 mu J) and spectrally broad supercontinuum extending from the deep ultraviolet (320 nm) to the infrared (1300 nm).

Single-mode hollow-core photonic crystal fiber made from soft glass

X. Jiang, T. G. Euser, A. Abdolvand, F. Babic, F. Tani, N. Y. Joly, J. C. Travers, P. St J. Russell

We demonstrate the first soft-glass hollow core photonic crystal fiber. The fiber is made from a high-index lead-silicate glass (Schott SF6, refractive index 1.82 at 500 nm). Fabricated by the stack-and-draw technique, the fiber incorporates a 7-cell hollow core embedded in a highly uniform 6-layer cladding structure that resembles a kagome-like lattice. Effective single mode guidance of light is observed from 750 to 1050 nm in a large mode area (core diameter similar to 30 mu m) with a low loss of 0.74 dB/m. The underlying guidance mechanism of the fiber is investigated using finite element modeling. The fiber is promising for applications requiring single mode guidance in a large mode area, such as particle guidance, fluid and gas filled devices. (C) 2011 Optical Society of America