Professor Philip St.J. Russell, FRS

Director of the Russell Division – Photonic Crystal Fibres

Professor Philip Russell is a founding Director of the Max-Planck Institute for the Science of Light (MPL), which began operations in January 2009. Since 2005 he has also held the Krupp Chair in Experimental Physics at the University of Erlangen-Nuremberg. He obtained his D.Phil. degree in 1979 at the University of Oxford, spending three years as a Research Fellow at Oriel College, Oxford. In 1982 and 1983 he was a Humboldt Fellow at the Technical University Hamburg-Harburg (Germany), and from 1984 to 1986 he worked at the University of Nice (France) and the IBM TJ Watson Research Center in Yorktown Heights, New York. From 1986 to 1996 he was based mainly at the University of Southampton, first of all in the Optical Fibre Group and then in the Optoelectronics Research Centre. From 1996 to 2005 he was professor in the Department of Physics at the University of Bath, where he established the Centre for Photonics and Photonic Materials. His research interests currently focus on scientific applications of photonic crystal fibres and related structures. He is a Fellow of the Royal Society and The Optical Society (OSA) and has won several international awards for his research including the 2000 OSA Joseph Fraunhofer Award/Robert M. Burley Prize, the 2005 Thomas Young Prize of the Institute for Physics (UK), the 2005 Körber Prize for European Science, the 2013 EPS Prize for Research into the Science of Light, the 2014 Berthold Leibinger Zukunftspreis and the 2015 IEEE Photonics Award. He was OSA's President in 2015, the International Year of Light.

2017

Rapid screening of photoactivatable metallodrugs: photonic crystal fibre microflow reactor coupled to ESI mass spectrometry

Ruth J. McQuitty, Sarah Unterkofler, Tijmen G. Euser, Philip St J. Russell, Peter J. Sadler

RSC ADVANCES 7 (59) 37340-37348 (2017) | Journal

We explore the efficacy of a hyphenated photonic crystal fibre microflow reactor-high-resolution mass spectrometer system as a method for screening the activity of potential new photoactivatable drugs. The use of light to activate drugs is an area of current development as it offers the possibility of reduced side effects due to improved spatial and temporal targeting and novel mechanisms of anticancer activity. The di-nuclear ruthenium complex [{(eta(6)-indan) RuCl}(2)(mu-2,3-dpp)](PF6)(2), previously studied by Magennis et al. (Inorg. Chem., 2007, 46, 5059) is used as a model drug to compare the system to standard irradiation techniques. The photodecomposition pathways using blue light radiation are the same for PCF and conventional cuvette methods. Reactions in the presence of small biomolecules 50-guanosine monophosphate (5'-GMP), 5'-adenosine monophosphate (5'-AMP), L-cysteine (L-Cys) and glutathione (gamma-L-glutamyl-L-cysteinyl-glycine, GSH) were studied. The complex was found to bind to nucleobases in the dark and this binding increased upon irradiation with 488 nm light, forming the adducts [(eta(6)-indan) Ru2(mu-2,3-dpp) + 5'-GMP](2+) and [(eta(6)-indan) Ru + (5'-AMP)]+. These findings are consistent with studies using conventional methods. The dinuclear complex also binds strongly to GSH after irradiation, a possible explanation for its lack of potency in cell line testing. The use of the PCF-MS system dramatically reduced the sample volume required and reduced the irradiation time by four orders of magnitude from 14 hours to 12 seconds. However, the reduced sample volume also results in a reduced MS signal intensity. The dead time of the combined system is 15 min, limited by the intrinsic dead volume of the HR-MS.

Effect of stray fields on Rydberg states in hollow-core PCF probed by higher-order modes

G. Epple, N. Y. Joly, T. G. Euser, P. St. J. Russell, R. Loew

OPTICS LETTERS 42 (17) 3271-3274 (2017) | Journal

The spectroscopy of atomic gases confined in hollow-core photonic crystal fiber (HC-PCF) provides optimal atom-light coupling beyond the diffraction limit, which is desirable for various applications such as sensing, referencing, and nonlinear optics. Recently, coherent spectroscopy was carried out on highly excited Rydberg states at room temperature in a gas-filled HC-PCF. The large polarizability of the Rydberg states made it possible to detect weak electric fields inside the fiber. In this Letter, we show that by combining highly excited Rydberg states with higher-order optical modes, we can gain insight into the distribution and underlying effects of these electric fields. Comparisons between experimental findings and simulations indicate that the fields are caused by the dipole moments of atoms adsorbed on the hollow-core wall. Knowing the origin of the electric fields is an important step towards suppressing them in future HC-PCF experiments. Furthermore, a better understanding of the influence of adatoms will be advantageous for optimizing electric-fieldsensitive experiments carried out in the vicinity of nearby surfaces. (C) 2017 Optical Society of America

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

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

PHYSICAL REVIEW LETTERS 118 (26) 263902 (2017) | Journal

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.

Higher-order mode suppression in twisted single-ring hollow-core photonic crystal fibers

N. N. Edavalath, M. C. Guenendi, R. Beravat, G. K. L. Wong, M. H. Frosz, J. -M. Menard, P. St. J. Russell

OPTICS LETTERS 42 (11) 2074-2077 (2017) | Journal

A hollow-core single-ring photonic crystal fiber (SR-PCF) consists of a ring of capillaries arranged around a central hollow core. Spinning the preform during drawing introduces a continuous helical twist, offering a novel means of controlling the modal properties of hollow-core SR-PCF. For example, twisting geometrically increases the effective axial propagation constant of the LP01-like modes of the capillaries, providing a means of optimizing the suppression of HOMs, which occurs when the LP11-like core mode phase-matches to the LP01-like modes of the surrounding capillaries. (In a straight fiber, optimum suppression occurs for a capillary-to-core diameter ratio d/D = 0.682.) Twisting also introduces circular birefringence (to be studied in a future Letter) and has a remarkable effect on the transverse intensity profiles of the higher-order core modes, forcing the two-lobed LP11-like mode in the untwisted fiber to become three-fold symmetric in the twisted case. These phenomena are explored by means of extensive numerical modeling, an analytical model, and a series of experiments. Prism-assisted side-coupling is used to measure the losses, refractive indices, and near-field patterns of individual fiber modes in both the straight and twisted cases. (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

OPTICS LETTERS 42 (9) 1768-1771 (2017) | Journal

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

Characterization and shaping of the time-frequency Schmidt mode spectrum of bright twin beams generated in gas-filled hollow-core photonic crystal fibers

M. A. Finger, N. Y. Joly, P. St. J. Russell, M. V. Chekhova

PHYSICAL REVIEW A 95 (5) 053814 (2017) | Journal

We vary the time-frequency mode structure of ultrafast pulse-pumped modulational instability (MI) twin beams in an argon-filled hollow-core kagome-style photonic crystal fiber by adjusting the pressure, pump pulse chirp, fiber length, and parametric gain. Compared to solid-core systems, the pressure-dependent dispersion landscape brings increased flexibility to the tailoring of frequency correlations, and we demonstrate that the pump pulse chirp can be used to tune the joint spectrum of femtosecond-pumped.(3) sources. We also characterize the resulting mode content, not only by measuring the multimode second-order correlation function g((2)), but also by directly reconstructing the shapes and weights of time-frequency Schmidt (TFS) modes. We show that the number of modes directly influences the shot-to-shot pulse-energy and spectral-shape fluctuations in MI. Using this approach we control and monitor the number of TFS modes within the range from 1.3 to 4 using only a single fiber.

Generation of broadband mid-IR and UV light in gas-filled single-ring hollow-core PCF

Marco Cassataro, David Novoa, Mehmet C. Guenendi, Nitin N. Edavalath, Michael H. Frosz, John C. Travers, Philip St. J. Russell

OPTICS EXPRESS 25 (7) 7637-7644 (2017) | Journal

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 mu 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 270 nm to 3.1 mu m, with a total energy of a few mu J. In addition, we demonstrate the emission of ultraviolet dispersive waves whose frequency can be tuned simply by adjusting the pump wavelength. SR-PCF thus constitutes an effective means of compressing and delivering tunable ultrafast pulses in the near and mid-infrared spectral regions. (C) 2017 Optical Society of America

Coherent control of flexural vibrations in dual-nanoweb fibers using phase-modulated two-frequency light

J. R. Koehler, R. E. Noskov, A. A. Sukhorukov, D. Novoa, P. St. J. Russell

PHYSICAL REVIEW A 96 (6) 063822 (2017) | Journal

Coherent control of the resonant response in spatially extended optomechanical structures is complicated by the fact that the optical drive is affected by the backaction from the generated phonons. Here we report an approach to coherent control based on stimulated Raman-like scattering, in which the optical pressure can remain unaffected by the induced vibrations even in the regime of strong optomechanical interactions. We demonstrate experimentally coherent control of flexural vibrations simultaneously along the whole length of a dual-nanoweb fiber, by imprinting steps in the relative phase between the components of a two-frequency pump signal, the beat frequency being chosen to match a flexural resonance. Furthermore, sequential switching of the relative phase at time intervals shorter than the lifetime of the vibrations reduces their amplitude to a constant value that is fully adjustable by tuning the phase modulation depth and switching rate. The results may trigger new developments in silicon photonics, since such coherent control uniquely decouples the amplitude of optomechanical oscillations from power-dependent thermal effects and nonlinear optical loss.

Helically twisted photonic crystal fibres

P. St. J. Russell, Ramin Beravat, G. K. L. Wong

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 375 (2087) 20150440 (2017) | Journal

Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left-and rightspinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue 'Optical orbital angular momentum'.

Broadband, Lensless, and Optomechanically Stabilized Coupling into Microfluidic Hollow-Core Photonic Crystal Fiber Using Glass Nanospike

Richard Zeltner, Shangran Xie, Riccardo Pennetta, Philip St J. Russell

ACS PHOTONICS 4 (2) 378-383 (2017) | Journal

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, deliirering similar to 300 mW at 1064 nm, can be used to optically align and stably maintain the iianospike at the core center. Once this is done, a weak broadband supercontinuum signal (similar to 575-1064 nm) can be efficiently and close to achromatically launched in the HC-PCF. The system is robust against liquid-flow in either direction inside the HC-PCF, and the Fresnel back-reflections are reduced to negligible levels compared to free-space launching or butt-coupling. The results are of potential relevance for any application where the efficient delivery of broadband light into liquid-core waveguides is desired.

Generation of spectral clusters in a mixture of noble and Raman-active gases (vol 41, pg 5543, 2016)

Pooria Hosseini, Amir Abdolvand, Philip St. J. Russell

OPTICS LETTERS 42 (3) 522-522 (2017) | Journal

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

OPTICA 4 (10) 1272-1276 (2017) | Journal

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

Universality of Coherent Raman Gain Suppression in Gas-Filled Broadband-Guiding Photonic Crystal Fibers

Pooria Hosseini, M. K. Mridha, D. Novoa, A. Abdolvand, P. St. J. Russell

PHYSICAL REVIEW APPLIED 7 (3) 034021 (2017) | Journal

As shown in the early 1960s, the gain in stimulated Raman scattering (SRS) is drastically suppressed when the rate of creation of phonons (via a pump-to-Stokes conversion) is exactly balanced by the rate of phonon annihilation (via a pump-to-anti-Stokes conversion). This occurs when the phonon coherence waves-synchronized vibrations of a large population of molecules-have identical propagation constants for both processes; i. e., they are phase-velocity matched. As recently demonstrated, hydrogen-filled photonic crystal fiber pumped in the vicinity of its zero-dispersion wavelength provides an ideal system for observing this effect. Here we report that Raman gain suppression is actually a universal feature of SRS in gas-filled hollow-core fibers and that it can strongly impair SRS even when the phase mismatch is high, particularly at high pump powers when it is normally assumed that nonlinear processes become more (not less) efficient. This counterintuitive result means that intermodal stimulated Raman scattering (for example, between LP01 and LP11 core modes) begins to dominate at high power levels. The results reported have important implications for fiber-based Raman shifters, amplifiers, or frequency combs, especially for operation in the ultraviolet, where the Raman gain is much higher.

Enhanced Control of Transient Raman Scattering Using Buffered Hydrogen in Hollow-Core Photonic Crystal Fibers

P. Hosseini, D. Novoa, A. Abdolvand, P. St. J. Russell

PHYSICAL REVIEW LETTERS 19 (25) 253903 (2017) | Journal

Many reports on stimulated Raman scattering in mixtures of Raman-active and noble gases indicate that the addition of a dispersive buffer gas increases the phase mismatch to higher-order Stokes and anti-Stokes sidebands, resulting in a preferential conversion to the first few Stokes lines, accompanied by a significant reduction in the Raman gain due to collisions with gas molecules. Here we report that, provided the dispersion can be precisely controlled, the effective Raman gain in a gas-filled hollow-core photonic crystal fiber can actually be significantly enhanced when a buffer gas is added. This counterintuitive behavior occurs when the nonlinear coupling between the interacting fields is strong and can result in a performance similar to that of a pure Raman-active gas, but at a much lower total gas pressure, allowing competing effects such as Raman backscattering to be suppressed. We report high modal purity in all the emitted sidebands, along with anti-Stokes conversion efficiencies as high as 5% in the visible and 2% in the ultraviolet. This new class of gas-based waveguide device, which allows the nonlinear optical response to be beneficially pressure-tuned by the addition of buffer gases, may find important applications in laser science and spectroscopy.

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

NATURE COMMUNICATIONS 8 813 (2017) | Journal

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.

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

OPTICA 4 (9) 1024-1029 (2017) | Journal

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

Fresnel-Reflection-Free Self-Aligning Nanospike Interface between a Step-Index Fiber and a Hollow-Core Photonic-Crystal-Fiber Gas Cell

Riccardo Pennetta, Shangran Xie, Frances Lenahan, Manoj Mridha, David Novoa, Philip St. J. Russell

PHYSICAL REVIEW APPLIED 8 (1) 014014 (2017) | Journal

We report a fully integrated interface delivering efficient, reflection-free, single-mode, and self-aligned coupling between a step-index fiber and a gas-filled hollow-core photonic crystal fiber. The device offers a universal solution for interfacing solid and hollow cores and can be sealed to allow operation either evacuated or at high pressure. Stimulated Raman scattering and molecular modulation of light are demonstrated in a H-2-filled hollow-core photonic crystal fiber using the device.

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

REVIEW OF SCIENTIFIC INSTRUMENTS 88 (7) 073106 (2017) | Journal

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.

Broadband high-resolution multi-species CARS in gas-filled hollow-core photonic crystal fiber

Barbara M. Trabold, Robert J. R. Hupfer, Amir Abdolvand, Philip St. J. Russell

OPTICS LETTERS 42 (17) 3283-3286 (2017) | Journal

We report the use of coherent anti-Stokes Raman spectros-copy (CARS) in gas-filled hollow-core photonic crystal fiber (HC-PCF) for trace gas detection. The long optical path-lengths yield a 60 dB increase in the signal level compared with free-space arrangements. This enables a relatively weak supercontinuum (SC) to be used as Stokes seed, along with a ns pump pulse, paving the way for broadband (> 4000 cm(-1)) single-shot CARS with an unprecedented resolution of similar to 100 MHz. A kagome-style HC-PCF provides broadband guidance, and, by operating close to the pressure-tunable zero dispersion wavelength, we can ensure simultaneous phase-matching of all gas species. We demonstrate simultaneous measurement of the concentrations of multiple trace gases in a gas sample introduced into the core of the HC-PCF. (C) 2017 Optical Society of America

Analytical formulation for the bend loss in single-ring hollow-core photonic crystal fibers

Michael H. Frosz, Paul Roth, Mehmet C. Guenendi, Philip St. J. Russell

PHOTONICS RESEARCH 5 (2) 88-91 (2017) | Journal

Understanding bend loss in single-ring hollow-core photonic crystal fibers (PCFs) is becoming of increasing importance as the fibers enter practical applications. While purely numerical approaches are useful, there is a need for a simpler analytical formalism that provides physical insight and can be directly used in the design of PCFs with low bend loss. We show theoretically and experimentally that a wavelength-dependent critical bend radius exists below which the bend loss reaches a maximum, and that this can be calculated from the structural parameters of a fiber using a simple analytical formula. This allows straightforward design of single-ring PCFs that are bend-insensitive for specified ranges of bend radius and wavelength. It also can be used to derive an expression for the bend radius that yields optimal higher-order mode suppression for a given fiber structure. (C) 2017 Chinese Laser Press

Photochemistry in a soft-glass single-ring hollow-core photonic crystal fibre

Ana M. Cubillas, Xin Jiang, Tijmen G. Euser, Nicola Taccardi, Bastian J. M. Etzold, Peter Wasserscheid, Philip St. J. Russell

ANALYST 142 (6) 925-929 (2017) | Journal

A hollow-core photonic crystal fibre (HC-PCF), guided by photonic bandgap effects or anti-resonant reflection, offers strong light confinement and long photochemical interaction lengths in a microscale channel filled with a solvent of refractive index lower than that of glass (usually fused silica). These unique advantages have motivated its recent use as a highly efficient and versatile microreactor for liquid-phase photochemistry and catalysis. In this work, we use a single-ring HC-PCF made from a high-index soft glass, thus enabling photochemical experiments in higher index solvents. The optimized light-matter interaction in the fibre is used to strongly enhance the reaction rate in a proof-of-principle photolysis reaction in toluene.

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