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.
Excitation of higher-order modes in optofluidic photonic crystal fiber
Andrei Ruskuc,
Philipp Koehler,
Marius A. Weber,
Ana Andres-Arroyo,
Michael H. Frosz,
Philip St. J. Russell,
Tijmen G. Euser
Optics Express
26
(23)
30245-30254
(2018)
| Journal
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Higher-order modes up to LP33 are controllably excited in water-filled kagomé- and bandgap-style hollow-core photonic crystal fibers (HC-PCF). A spatial light modulator is used to create amplitude and phase distributions that closely match those of the fiber modes, resulting in typical launch efficiencies of 10–20% into the liquid-filled core. Modes, excited across the visible wavelength range, closely resemble those observed in air-filled kagomé HC-PCF and match numerical simulations. Mode indices are obtained by launching plane-waves at specific angles onto the fiber input-face and comparing the resulting intensity pattern to that of a particular mode. These results provide a framework for spatially-resolved sensing in HC-PCF microreactors and fiber-based optical manipulation.
Strong circular dichroism for the HE11 mode in twisted single-ring hollow-core photonic crystal fiber
Paul Roth,
Yang Chen,
Mehmet Can Günendi,
Ramin Beravat,
Nitin N. Edavalath,
Michael H. Frosz,
Goran Ahmed,
Gordon K. L. Wong,
Philip St. J. Russell
We report a series of experimental, analytical, and numerical studies demonstrating strong circular dichroism for the HE11-like core mode in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing. In the SR-PCFs studied, the hollow core is surrounded by a single ring of nontouching capillaries. Coupling between these capillaries results in the formation of helical Bloch modes carrying orbital angular momentum. When twisted, strong circular birefringence appears in the ring, so that coupling to the core mode is possible for only one circular polarization state. The result is a SR-PCF that acts as a circular polarizer, offering 1.4 dB/m for the low-loss polarization state and 9.7 dB/m for the high-loss state over a 25 nm band centered at 1593 nm wavelength. In addition, we report for the first time that the vector fields of the helical Bloch modes are perfectly periodic when evaluated in cylindrical coordinates. Such fibers have many potential applications, such as generating circularly polarized light in gas-filled SR-PCF and realizing polarizing elements in the deep and vacuum ultraviolet.
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).
Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre
Dmitry S. Bykov,
Shangran Xie,
Richard Zeltner,
Andrey Machnev,
Gordon K. L. Wong,
Tijmen G. Euser,
Philip St. J. Russell
Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 μm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.
Alberto Lombardini,
Vasyl Mytskaniuk,
Siddharth Sivankutty,
Esben Ravn Andresen,
Xueqin Chen,
Jérôme Wenger,
Marc Fabert,
Nicolas Y. Joly,
Frédéric Louradour, et al.
Coherent Raman scattering microscopy is a fast, label-free, and chemically specific imaging technique that shows high potential for future in vivo optical histology. However, the imaging depth in tissues is limited to the sub-millimeter range because of absorption and scattering. Realization of coherent Raman imaging using a fiber endoscope system is a crucial step towards imaging deep inside living tissues and providing information that is inaccessible with current microscopy tools. Until now, the development of coherent Raman endoscopy has been hampered by several issues, mainly related to the fiber delivery of the excitation pulses and signal collection. Here, we present a flexible, compact, coherent Raman, and multimodal nonlinear endoscope (4.2 mm outer diameter, 71 mm rigid length) based on a resonantly scanned hollow-core Kagomé lattice double-clad fiber. The fiber design enables distortion-less, background-free delivery of femtosecond excitation pulses and back-collection of nonlinear signals through the same fiber. Sub-micrometer spatial resolution over a large field of view is obtained by combination of a miniature objective lens with a silica microsphere lens inserted into the fiber core. We demonstrate high-resolution, high-contrast coherent anti-Stokes Raman scattering, and second harmonic generation endoscopic imaging of biological tissues over a field of view of 320 µm at a rate of 0.8 frames per second. These results pave the way for intraoperative label-free imaging applied to real-time histopathology diagnosis and surgery guidance.
Dispersion tuning in sub-micron tapers for third-harmonic and photon triplet generation
Jonas Hammer,
Andrea Cavanna,
Riccardo Pennetta,
Maria Chekhova,
Philip St. J. Russell,
Nicolas Joly
Precise control of the dispersion landscape is of crucial importance if optical fibers are to be successfully used for the generation of three-photon states of light—the inverse of third-harmonic generation (THG). Here we report gas-tuning of intermodal phase-matched THG in sub-micron-diameter tapered optical fiber. By adjusting the pressure of the surrounding argon gas up to 50 bars, intermodally phase-matched third-harmonic light can be generated for pump wavelengths within a 15 nm range around 1.38 μm. We also measure the infrared fluorescence generated in the fiber when pumped in the visible and estimate that the accidental coincidence rate in this signal is lower than the predicted detection rate of photon triplets
Dominance of backward stimulated Raman scattering in gas-filled hollow-core photonic crystal fibers
Backward stimulated Raman scattering in gases provides a promising route to the compression and amplification of a Stokes seed pulse by counter-propagating against a pump pulse, as has been demonstrated already in various platforms, mainly in free space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report, to the best of our knowledge, the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable to, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532 nm pump. Efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers, the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength toward the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.
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.
Stable Immobilization of Size‐Controlled Bimetallic Nanoparticles in Photonic Crystal Fiber Microreactor
Sebastian Ponce,
Macarena Munoz,
Ana M. Cubillas,
Tijmen G. Euser,
Gui-Rong Zhang,
Philip St. J. Russell,
Peter Wasserscheid,
Bastian J. M. Etzold
The possibility of immobilizing ex situ‐synthesized colloidal bimetallic nanoparticles (NPs) of well‐defined characteristics inside hollow core photonic crystal fiber (HC‐PCF) microreactors is demonstrated. With the developed method, PtNi clusters remain strongly attached to the fiber core and can be used as active catalysts for the hydrogenation of an azobenzene dye. The study revealed that optical transmission exhibits a size‐dependent behavior, i.e., smaller NPs bring in less optical signal loss. Sufficient light transmission was achieved for all particle sizes. Furthermore, with these catalytic PCF microreactors, kinetic data can be obtained with a much lower amount of precious metals compared to a conventional batch reactor, opening a new pathway for in situ catalyst screening.
Highly Sensitive Luminescence Detection of Photosensitized Singlet Oxygen within Photonic Crystal Fibers
Gareth O. S. Williams,
Tijmen G. Euser,
Philip St. J. Russell,
Alexander J. MacRobert,
Anita C. Jones
Highly sensitive, quantitative detection of singlet oxygen (1O2) is required for the evaluation of newly developed photosensitizers and the elucidation of the mechanisms of many processes in which singlet oxygen is known or believed to be involved. The direct detection of 1O2 through its intrinsic phosphorescence at 1270 nm is challenging, because of the extremely low intensity of this emission, coupled with the low quantum efficiency of currently available photodetectors at this wavelength. We introduce hollow‐core photonic crystal fibers (HC‐PCF) as a novel optofluidic modality for photosensitization and detection of 1O2. We report the use of this approach to achieve highly sensitive detection of the luminescence decay of 1O2 produced by using two common photosensitizers, Rose Bengal and Hypericin, within the 60‐μm diameter core of a 15 cm length of HC‐PCF. We demonstrate the feasibility of directly detecting sub‐picomole quantities of 1O2 by using this methodology, and identify some aspects of the HC‐PCF technology that can be improved to yield even higher detection sensitivity.
Flying particle microlaser and temperature sensor in hollow-core photonic crystal fiber
Richard Zeltner,
Riccardo Pennetta,
Shangran Xie,
Philip Russell
Whispering-gallery mode (WGM) resonators combine small optical mode volumes with narrow resonance linewidths, making them exciting platforms for a variety of applications. Here we report a flying WGM microlaser, realized by optically trapping a dye-doped microparticle within a liquid-filled hollow-core photonic crystal fiber (HC-PCF) using a CW laser and then pumping it with a pulsed excitation laser whose wavelength matches the absorption band of the dye. The laser emits into core-guided modes that can be detected at the endfaces of the HC-PCF. Using radiation forces, the microlaser can be freely propelled along the HC-PCF over multi-centimeter distances—orders of magnitude farther than in previous experiments where tweezers and fiber traps were used. The system can be used to measure temperature with high spatial resolution, by exploiting the temperature-dependent frequency shift of the lasing modes, and may also permit precise delivery of light to remote locations.
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.
Control of ultrafast pulses in a hydrogen-filled hollow-core photonic-crystal fiber by Raman coherence
Federico Belli,
Amir Abdolvand,
John Travers,
Philip Russell
We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal<br>grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at ∼300 nm and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.
Three-dimensional holographic optical manipulation through a high-numerical-aperture soft-glass multimode fibre
Ivo T. Leite,
Sergey Turtaev,
Xin Jiang,
Martin Siler,
Alfred Cuschieri,
Philip St. J. Russell,
Tomas Cizmar
Holographic optical tweezers (HOT) hold great promise for many applications in biophotonics, allowing the creation and measurement of minuscule forces on biomolecules, molecular motors and cells. Geometries used in HOT currently rely on bulk optics, and their exploitation in vivo is compromised by the optically turbid nature of tissues. We present an alternative HOT approach in which multiple three-dimensional (3D) traps are introduced through a high-numerical-aperture multimode optical fibre, thus enabling an equally versatile means of manipulation through channels having cross-section comparable to the size of a single cell. Our work demonstrates real-time manipulation of 3D arrangements of micro-objects, as well as manipulation inside otherwise inaccessible cavities. We show that the traps can be formed over fibre lengths exceeding 100 mm and positioned with nanometric resolution. The results provide the basis for holographic manipulation and other high-numerical-aperture techniques, including advanced microscopy, through single-core-fibre endoscopes deep inside living tissues and other complex environments.
Kontakt
Bitte richten Sie forschungsbezogene Anfragen an philip.russell@mpl.mpg.de und allgemeine Anfragen an Bettina Schwender:
Max-Planck-Institut für die Physik des Lichts Staudtstr. 2 91058 Erlangen
