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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.

2020

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.

Nature Photonics 15 277-280 (2020) | Journal

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.

Sub-40  fs pulses at 1.8  µm and MHz repetition rates by chirp-assisted Raman scattering in hydrogen-filled hollow-core fiber

Sébastien Loranger, Philip Russell, David Novoa

Journal of the Optical Society of America B-Optical Physics 37 (12) 3550-3556 (2020) | Journal

The possibility to perform time-resolved spectroscopic studies in the molecular fingerprinting region or extending the cutoff wavelength of high-harmonic generation has recently boosted the development of efficient mid-infrared (mid-IR) ultrafast lasers. In particular, fiber lasers based on active media such as thulium or holmium are a very active area of research since they are robust, compact, and can operate at high repetition rates. These systems, however, are still complex, are unable to deliver pulses shorter than 100 fs, and are not yet as mature as their near-infrared counterparts. Here, we report the generation of sub-40 fs pulses at 1.8 µm, with quantum efficiencies of 50% and without the need for post-compression, in hydrogen-filled, hollow-core photonic crystal fiber pumped by a commercial high-repetition-rate 300 fs fiber laser at 1030 nm. This is achieved by pressure-tuning the dispersion and avoiding Raman gain suppression by adjusting the chirp of the pump pulses and the proportion of higher-order modes launched into the fiber. The system is optimized using a physical model that incorporates the main linear and nonlinear contributions to the optical response. The approach is average power-scalable, permits adjustment of the pulse shape, and can potentially allow access to much longer wavelengths.

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

Optics Express 28 (23) 34328-34336 (2020) | Journal

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

Optics Letters 45 (14) 4044-4047 (2020) | Journal

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.

Narrowband Vacuum Ultraviolet Light via Cooperative Raman Scattering in Dual-Pumped Gas-Filled Photonic Crystal Fiber

Rinat Tyumenev, Philip Russell, David Novoa

ACS Photonics 7 (8) 1989-1993 (2020) | Journal

Many fields such as biospectroscopy and photochemistry often require sources of vacuum ultraviolet (VUV) pulses featuring a narrow line width and tunable over a wide frequency range. However, the majority of available VUV light sources do not simultaneously fulfill those two requirements and few if any are truly compact, cost-effective, and easy to use by nonspecialists. Here we introduce a novel approach that goes a long way to meeting this challenge. It is based on hydrogen-filled hollow-core photonic crystal fiber pumped simultaneously by two spectrally distant pulses. Stimulated Raman scattering enables the generation of coherence waves of collective molecular motion in the gas, which together with careful dispersion engineering and control over the modal content of the pump light, facilitates cooperation between the two separate Raman combs, resulting in a spectrum that reaches deep into the VUV. Using this system, we demonstrate the generation of a dual Raman comb of narrowband lines extending down to 141 nm using only 100 mW of input power delivered by a commercial solid-state laser. The approach may enable access to tunable VUV light to any laboratory and therefore boost progress in many research areas across multiple disciplines.

Sub-two-cycle octave-spanning mid-infrared fiber laser

Jiapeng Huang, Meng Pang, Xin Jiang, Felix Köttig, Daniel Schade, Wenbin He, Martin Butryn, Philip Russell

Optica 7 (6) 574-579 (2020) | Journal

Compact and powerful ultrafast light sources at high pulse repetition rates, based on mode-locked near infrared fiber lasers, are now widely available and are being used in applications such as frequency metrology, molecular spectroscopy, and laser micro-machining. The realization of such lasers in the mid-infrared has, however, remained a challenge for many years. Here we report a record-breaking three-stage fiber laser system that uses an Er-doped fluoride fiber as gain medium, delivering W-level few-cycle pulses at 2.8 µm at a repetition rate of 42.1 MHz. A fiber-based seed oscillator, cavity dispersion-managed by a pulse-stretcher, generates near-100-fs mid-infrared pulses with >110nm spectral bandwidth. These pulses are amplified to an average power of ∼1 W in a chirp-engineered fiber amplifier, and then compressed to ∼16 fs in a short length of highly nonlinear ZBLAN fiber, resulting in a more-than-octave-wide spectrum reaching from 1.8 µm to 3.8 µm with a total power of 430 mW.

Optomechanical cooling and self-stabilization of a waveguide coupled to a whispering-gallery-mode resonator

Riccardo Pennetta, Shangran Xie, Richard Zeltner, Jonas Hammer, Philip Russell

Photonics Research 8 (6) 844-851 (2020) | Journal

Laser cooling of mechanical degrees of freedom is one of the most significant achievements in the field of optomechanics. Here, we report, for the first time to the best of our knowledge, efficient passive optomechanical cooling of the motion of a freestanding waveguide coupled to a whispering-gallery-mode (WGM) resonator. The waveguide is an 8 mm long glass-fiber nanospike, which has a fundamental flexural resonance at Ω/2π=2.5  kHz and a Q-factor of 1.2×10^5. Upon launching ∼250  μW laser power at an optical frequency close to the WGM resonant frequency, we observed cooling of the nanospike resonance from room temperature down to 1.8 K. Simultaneous cooling of the first higher-order mechanical mode is also observed. The strong suppression of the overall Brownian motion of the nanospike, observed as an 11.6 dB reduction in its mean square displacement, indicates strong optomechanical stabilization of linear coupling between the nanospike and the cavity mode. The cooling is caused predominantly by a combination of photothermal effects and optical forces between nanospike and WGM resonator. The results are of direct relevance in the many applications of WGM resonators, including atom physics, optomechanics, and sensing.

Three-photon head-mounted microscope for imaging deep cortical layers in freely moving rats

Alexandr Klioutchnikov, Damian J Wallace, Michael H. Frosz, Richard Zeltner, Jürgen Sawinski, Verena Pawlak, Kay-Michael Voit, Philip St. J. Russell, Jason N. D. Kerr

Nature methods 17 509-513 (2020) | Journal | PDF

We designed a head-mounted three-photon microscope for imaging deep cortical layer neuronal activity in a freely moving rat. Delivery of high-energy excitation pulses at 1,320 nm required both a hollow-core fiber whose transmission properties did not change with fiber movement and dispersion compensation. These developments enabled imaging at >1.1 mm below the cortical surface and stable imaging of layer 5 euronal activity for >1 h in freely moving rats performing a range of behaviors.

Three-photon head-mounted microscope for imaging deep cortical layers in freely moving rats

Alexandr Klioutchnikov, Damian James Wallace, Michael H. Frosz, Richard Zeltner, Jürgen Sawinski, Verena Pawlak, Kay-Michael Voit, Philip St. J. Russell, Jason Kerr

Nature methods 17 509-513 (2020) | Journal

We designed a head-mounted three-photon microscope for imaging deep cortical layer neuronal activity in a freely moving rat. Delivery of high-energy excitation pulses at 1,320 nm required both a hollow-core fiber whose transmission properties did not change with fiber movement and dispersion compensation. These developments enabled imaging at >1.1 mm below the cortical surface and stable imaging of layer 5 euronal activity for >1 h in freely moving rats performing a range of behaviors.

Thermally tunable whispering-gallery mode cavities for magneto-optics

Serge Vincent, Xin Jiang, Philip Russell, Frank Vollmer

Applied Physics Letters 116 161110 1-4 (2020) | Journal

We report the experimental realization of magneto-optical coupling between whispering-gallery modes in a germanate (56GeO2-31PbO9Na2O-4Ga2O3) microspherical cavity due to the Faraday effect. An encapsulated gold conductor heats the resonator and tunes the quasitransverse electric (TE) and quasi-transverse magnetic (TM) polarized modes with an efficiency of 65 fm/V at a peak-to-peak bias voltage of 4 V. The signal parameters for a number of heating regimes are quantified to confirm sensitivity to the generated magnetic field. The quasi-TE and quasi-TM resonance frequencies stably converge near the device’s heating rate limit (equivalently, bias voltage limit) in order to minimize inherent geometrical birefringence. This functionality optimizes Faraday rotation and thus enables the observation of subsequent magneto-optics.

Bragg Reflection and Conversion Between Helical Bloch Modes in Chiral Three-Core Photonic Crystal Fiber

Sébastien Loranger, Yang Chen, Paul Roth, Michael Frosz, Gordon Wong, Philip Russell

Journal of Lightwave Technology 38 (15) 4100-4107 (2020) | Journal

Optical fiber modes carrying orbital angular momentum (OAM) have many applications, for example in mode-division-multiplexing for optical communications. The natural guided modes of N-fold rotationally symmetric optical fibers, such as most photonic crystal fibers, are helical Bloch modes (HBMs). HBMs consist of a superposition of azimuthal harmonics (order m) of order l_A(m)=l_A(0)+mN. When such fibers are twisted, these modes become circularly and azimuthally birefringent, that is to say HBMs with equal and opposite values of l_A(0) and spin s are non-degenerate. In this article we report the use of Bragg mirrors to reflect and convert HBMs in a twisted three-core photonic crystal fiber, and show that by writing a tilted fiber Bragg grating (FBG), reflection between HBMs of different orders becomes possible, with high wavelength-selectivity. We measure the near-field phase and amplitude distribution of the reflected HBMs interferometrically, and demonstrate good agreement with theory. This new type of FBG has potential applications in fiber lasers, sensing, quantum optics, and in any situation where creation, conversion, and reflection of OAM-carrying modes is required.

Robust excitation and Raman conversion of guided vortices in a chiral gas-filled photonic crystal fiber

Sona Davtyan, Yang Chen, Michael Frosz, Philip Russell, David Novoa

Optics Letters 45 (7) 1766-1769 (2020) | Journal

The unique ring-shaped intensity patterns and helical phase fronts of optical vortices make them useful in many applications. Here we report for the first time, to the best of our knowledge, efficient Raman frequency conversion between vortex modes in a twisted hydrogen-filled single-ring hollow core photonic crystal fiber (SR-PCF). High-fidelity transmission of optical vortices in an untwisted SR-PCF becomes<br>more and more difficult as the orbital angular momentum (OAM) order increases, due to scattering at structural imperfections in the fiber microstructure. In a helically twisted<br>SR-PCF, however, the degeneracy between left- and righthanded versions of the same mode is lifted, with the result<br>that they are topologically protected from such scattering. With launch efficiencies of ∼75%, a high damage threshold and broadband guidance, these fibers are ideal for performing nonlinear experiments that require the polarization<br>state and azimuthal order of the interacting modes to be preserved over long distances. Vortex coherence waves of internal molecular motion carrying angular momentum are excited in the gas, permitting the polarization and OAM of the Raman bands to be tailored, even in spectral regions where conventional solid-core waveguides are opaque or susceptible to optical damage.

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

Optics Express 28 (7) 9099-9110 (2020) | Journal

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%.

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