Doctoral Students & Postdocs

PhD students

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Christopher Aleshire

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email: 
Phone: +49 3641-9-47826

Power Scaling of Ultrafast Fiber Lasers via Coherent Beam Combination

Coherent Beam Combination (CBC) has recently enabled the scaling of laser systems past the peak- and average-power limitations of single-emitter lasers. By matching their electric fields to sub-wavelength precision, large arrays of lasers can be made to act as a single laser system with extremely high intensity. Fiber lasers are particularly well-suited to CBC due to their intrinsically good beam quality, high efficiency, and compact footprint. CBC of ultrafast fiber lasers with pulse durations of only a few femtoseconds is particularly difficult, but significant advances have been recently made in the Fiber and Waveguide Lasers Group at FSU Jena. This GRK project will continue these advances by developing a densely-packed coherently-combined ultrafast fiber laser source with high repetition rate and high pulse energy. The development will rely on state-of-the-art CBC and Chirped Pulse Amplification (CPA) techniques, and will utilize advanced optical materials capable of generating and handling these powers. The laser system will support numerous research objectives, including generation of high-flux coherent Extreme Ultraviolet (XUV) light and development of next-generation particle accelerators based on laser-plasma wakefield acceleration.

 

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Neus Allande Calvet

Leibniz Institute of Photonic Technology (IPHT)
Research Field: Ultrafast Spectroscopy
Email:
Phone: +49 3641-206131

Femtosecond time-resolved cavity ring down spectroscopy

 Set up and characterization of a very sensitive spectroscopic system called cavity ring down spectroscopy (CRDS) in combination with femtosecond pump-probe spectroscopy. Such setup is intended to temporally resolve the transient absorption of thin films and monomolecular layers by measuring the decay of excited states with a lifetime as short as few tens of femtoseconds.

 

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Timothy Imogore

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Ultrafast optics
Email:  
Phone: +49 3641-9-47824

 Novel femtosecond written fiber Bragg gratings with tailored dispersion in advanced fibers 

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Kim Lammers

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Ultrafast optics
Email:  
Phone: +49 3641-9-47824

 Quantum operations in fs laser written integrated photonic circuits 

In my project I am fabricating waveguides in glass chips using the femtosecond direct-writing method. This method uses femtosecond laser pulses to create stable, high-fidelity and permanent waveguides whilst enabling tuning of the properties of every single waveguide. The aim of the project is to write tailored integrated photonic circuits by making use of the different modifications and structural changes that can be achieved with different processing parameters. The main advantages of integrated photonic circuits over large-scale bulk optics are possibly smaller dimensions, scalability and that the difficulties in the alignment and positioning of different optical components can be inherently overcome. These integrated circuits should be able to perform quantum operations with photons as qubits.  Especially birefringent modifications in the form of nanogratings are a promising candidate to enable the implementation of polarization encoded structures on a small chip. Integrated photonic quantum circuits could find important future applications in quantum information science and quantum computing. 

 

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André Muniz

Institute of Condensed Matter Theory and Solid State Optics (IFTO) , Friedrich Schiller University Jena
Research Field: Quantum Random Walks in discrete fiber networks
Email: 
Phone: +49 3641-9-47179

Nonlinearity and topology in two-dimensional photonic lattices

Fiber-based communication links for high-speed telecommunications have been highly demanded due to the steadily increasing usage of the internet and broadcasting of multimedia content. By using special techniques, the bandwidth bottleneck of optical fibers is overcome by encoding information in polarization, wavelength or the arrival time of an optical pulse. The latter method, also known as time multiplexing, is successfully used to implement photonic lattices, which have proven as a versatile platform for studying multifarious effects related to solid-state physics, the physics of cold atoms and nonlinear optics. In this project, we focus on the development of a two-dimensional photonic lattice by means of time multiplexing based on four coupled fiber loops of different lengths. For this goal, technical challenges are overcome by implementing a long-term stabilization of the fiber loops, which compensates temporal drifts such as rotation of the polarization. Additionally, a further step of this project is to expand experimental platforms by an advanced signal generation module, allowing for tailoring complex initial wave packets on demand and thereby to realize the light dynamics in a more deliberate manner. The main highlights of this project comprise of parity-time symmetry, nonlinear localization and topological effects in two discrete spatial dimensions.

 

 

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Mona Nissen

Leibniz Institute of Photonic Technology (IPHT), Friedrich Schiller University Jena
Research Field: Fiber sensors
Email:
Phone: +49 3641- 206 224

In-fiber detection of individual nanoobjects

Microstructured optical fibers are a versatile tool to manipulate the flow of light. One example is so called nanobore fibers that guide light along a solid core containing a nanofluidic channel. This channel can be filled by liquids with freely diffusing nanoobjects, such as viruses, large proteins, metal or dielectric nanoparticles, which scatter light elastically out of the fiber and can thus be detected and tracked. Especially the label-free tracking of individual nanoobjects can lead to a deeper understanding of physical, chemical and biological processes at the nanoscale, and opens new perspectives for disease diagnostics.
The current project's objective is the extension of the method’s applicability to the sub-20nm particle domain with the final target of detecting individual molecules.

 

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Ramona Scheibinger

Leibniz Institute of Photonic Technology (IPHT)
Research Field: Fiber sensors
Email:
Phone: +49 3641-206219

Tunable Mid-IR Supercontinuum Generation in Liquid-Core Optical Fibers

Spectral broadening of laser pulses by supercontinuum generation in optical fibers is a prominent method to transfer light to the mid-IR. Liquidcore optical fibers offer multiple advantages for supercontinuum generation in comparison to commonly used fibers (e.g. chalcogenide photonic crystal fibers). Besides their high transmission up to the mid-IR and their strong nonlinearity liquidcore fibers are sensitive to temperature due to the high thermooptical coefficients of the liquid in the core. Consequently, heating and cooling the fiber allows tailoring the dispersion with high flexibility in space and time. The aim of my PhD project is to apply well-adapted temperature landscapes along the liquidcore fibers to address specific wavelengths or to generate very broad and flat spectra in the midIR. Locally controlling the dispersion of the fiber may also allow investigating soliton dynamics that are known as driving forces for supercontinuum generation in the anomalous dispersion regime.

 

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Vittoria Schuster

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email: 
Phone: +49 3641-9-47813

 Ultraviolet dual comb spectroscopy

 Dual comb spectroscopy (DCS) is an advancement of Fourier transform spectroscopy (FTS), which due to its high spectral coverage and its high spectral resolution has been one of the leading methods in absorption spectroscopy for over forty years. By using two frequency combs with slightly different repetition rates in DCS, the necessity of a moving mirror is abandoned and this for example enables one million times shorter acquisition times while reaching the same spectral resolution.

The aim of this project is the introduction of DCS, which has proven an impressive tool in the THz, IR and optical region, to the (X)UV via high harmonic generation, thus allowing for the further spectroscopic investigation of physical properties of atoms, molecules and solids.

 

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Denizhan Sirmaci

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Funtional Photonic Nanostructures
Email: 
Phone: +49 3641-9-47573

Dielectric metamaterial‐inspired guided‐wave nanostructures based on Mie resonances

Dielectric nanoparticles were successfully and extensively used as optical nanoantennas and building blocks of highly efficient metasurfaces – nanostructured thin films that can tailor the wavefront, polarization and spectrum of a light field at will. So far, however, engineered Mie‐resonant nanoparticle structures and devices were almost exclusively studied in a free‐space geometry, while their deployment as guided wave structures and their integration in guided wave architectures remains largely unexplored. In my project, we aim to close this gap and to conceive, design, fabricate and experimentally characterize a range of dielectric metamaterial‐inspired guided‐wave architectures.

Light propagation along chains or arrays of dielectric nanoscale building blocks exhibiting electric and magnetic multipolar Mie-type resonances as well as specific functionalities like routing, mode conversion, or multiplexing of on‐chip guided light‐fields shall be explored using Mie-resonant nanoantenna architectures will be explored in this project.

 

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Ziyao Wang

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email: 
Phone: +49 3641-9-47649

High Power Mid-IR source via parametric down conversion pumped by 1.9 μm ultrafast fiber laser

Mid-IR laser sources associated with high pulse energies and ultrashort pulses are of long standing interest, regarding its substantial number of applications in medical diagnostics, spectroscopy and fundamental science. However, the output power from the direct mid-IR laser emission is strongly limited due to the lack of suitable active laser media. High-power ultrafast laser sources operating at around 2μm have recently been identified as a promising alternative for mid-IR generation by nonlinear frequency conversion, providing ultrashort pulses and coherent broadband mid-IR radiations.

The PhD project is dedicated to the evaluation and realization of experimental setups for high power mid-infrared light sources. For this purpose, power-scalable concepts for the nonlinear frequency conversion to the mid-infrared region pumped by Thulium-doped ultrafast fiber lasers operating at around 1.9 μm will be studied. In particular, concepts for ultrashort-pulse generation down to the few-cycle regime with unprecedented average powers are to be developed and experimentally implemented.

 

Associated PhD students

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Najmeh Abbasirad

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Nano Optics
Email:
Phone: +49 3641- 9-47568

Dual-probe scanning near-field optical microscopy for nanostructures characterization

Light interaction with nanostructures in the near-field region can only be investigated by scanning near-field optical microscopy (SNOM). In aperture SNOM, a small scanning aperture is used which can overcome the diffraction limit and provides a spatial resolution which is merely restricted by the aperture size. We are developing a fully automated dual-probe SNOM which uses two aperture tips for simultaneous illumination and collection of light. Some advantages of dual-probe measurement are the absence of a background signal from the illuminating laser, no diffraction limit for the illumination spot size and point-like emitter and detector to map the Green’s function. This technique has great potential to investigate nanostructures such as plasmonic devices, dielectric metasurfaces and surface waves on all-dielectric media.

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Arstan Bisianov

Institute of Condensed Matter Theory and Solid State Optics , Friedrich Schiller University Jena
Research Field: Quantum Random Walks in discrete fiber networks
Email: 
Phone: +49 3641-9-47179

Topological effects in fiber networks

Topological phases of matter to date remain one of the most active and fascinating fields of study in physics, being considered as an underlying explanatory framework for many fundamental phenomena like quantum Hall effect, topological insulation and Berry phase. By relying on a versatility of our optical setup based on time-multiplexed fiber networks, we implement the so-called Su-Schrieffer-Heeger model (SSH), in which the influence of the underlying topology is directly demonstrated. This includes, in particular, topologically protected interface and surface states. Interestingly, these states are protected by the symmetries inherent to the SSH lattice, thereby manifesting their strong robustness against external perturbations. In the ongoing experiments, the interplay between nonlinear phenomena, associated with the optical Kerr effect, and those topologically protected states is under consideration. From an experimental perspective such a combination is an almost unexplored field. Furthermore, symmetries do not only determine topological nature of a material, but when appropriately designed, they can even have striking effects like unidirectional invisibility. Such systems belong to a wide class of parity-time-symmetric materials, which are so far experimentally realized in one-dimensional lattices only. In this regard, our future plans concern the implementation of PT symmetry with higher dimensions.

 

Mario Chemnitz

Mario Chemnitz

Leibniz Institute of Photonic Technology (IPHT)
Email:
Phone: +49 3641-206278

Soliton dynamics in highly non-instantaneous liquid-core fibers

The high nonlinearity and low loss of some simple solvents (e.g., carbon disulfide) promise high efficiencies and a new degree of tuneability for nonlinear light generation up to mid-infrared wavelength region. The fission of solitons and their complex dynamics usually allow for the generation of ultra-broad supercontinuum spectra as soon as the waveguide dispersion is well designed and the nonlinearity of the core medium is high. In liquids, however, classical soliton fission processes are altered due to the yet unknown impact of the liquid's slow nonlinear response on the soliton dynamics. In my project I am investigating this non-instantaneous soliton dynamics to provide a deep understanding of the underlying physics and a pathway for efficient supercontinuum generation in liquid-core fibers tailorable for applications in biophotonics and atmospheric spectroscopy.

 

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Brenda Doherty

Leibniz Institute of Photonic Technology (IPHT)
Email:
Phone: +49 3641-206264

Plasmonic Microstructured Fibres for Biosensing

Detection of low quantities of target molecules, rapidly and specifically, is of major importance within bioanalytics for efficient disease diagnostics. Our sensing strategy is based on combining DNA-functionalised plasmonically-active waveguides with microfluidics yielding an easy-to-use sensing platform.
In this project we introduce suspended-core microstructured fibres containing immobilised gold nanoparticles deposited on the guiding core, as a concept for an entirely integrated optofluidic pathogen detection platform. Due to an extremely small optical fibre core and large adjacent microfluidic channels, so far over two orders of magnitude of gold nanosphere coverage densities have been realised in-fibre, with millimetre-long sample lengths yielding refractive index sensitivities of 170 nm/RIU for aqueous environments. We aim to further functionalise these particles with ssDNA and use this system to detect water contaminants such as legionella bacteria.
Our concept represents a fully integrated optofluidic sensing system requiring very low sample volumes and enabling real-time analyte monitoring, both of which are highly relevant within invasive bioanalytics, particularly within the fields of environmental science and molecular disease diagnostics.

 

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Friedrich Georg Fröbel

Institute of Physical Chemistry (IPC) , Friedrich Schiller University Jena
Research Field: Theoretical Chemistry
Email:  
Phone: +49 3641-9-48335 

Where the Born-Oppenheimer-approximation fails. Quantum dynamics of coupled nuclear-electronic dynamics in molecular model systems.

One of the most widely used approximations in molecular physics and chemistry is the Born-Oppenheimer (BO) approximation, in which the system's electronic dynamics are separated from the nuclear dynamics. This is possible as these dynamics take place on different time scales. In many cases, molecular vibration and rotation can be treated within the BO approximation. However, many photochemical and –physical pathways require including non-BO effects due to nuclear-electronic coupling.

This project develops and investigates molecular model systems enabling a fully quantum dynamical description of coupled nuclear-electronic motion ranging from weak to strong coupling strength. While the former case describes a situation, where the BO approximation is valid, the latter represents a system with one or more avoided crossings on its potential energy surfaces. Applying these model systems, we investigate characteristics and spectroscopic observables of non-BO dynamics in the presence of ultrashort weak and more intense laser pulses.

 

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Martin Gebhardt

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email:
Phone: +49 3641-9-47817

Performance scaling of ultrafast 2 µm fiber laser systems

Powerful laser sources delivering intense ultrashort pulses in the mid-infrared spectral region are enabling tools for demanding research activities in high-field or atto-science, as well as for a variety of subsequent applications like high-resolution coherent diffractive imaging and X-ray absorption edge spectroscopy. As a next step within the evolution of these emerging technologies, the driving laser sources must deliver few-cycle pulses with more average power/higher repetition rate in order to transform what nowadays are laboratory experiments into real world applications, which require high signal to noise ratio and fast data acquisition. Thulium-doped fiber laser systems, with an emission wavelength around 2 µm, are an average power scalable solid-state laser concept and also represent a promising choice for pushing the limits of their well-established ytterbium-based counterparts in terms of pulse duration and peak power. The research carried out at the IAP focuses on exploiting the full potential of this laser concept based on well-known fused silica fiber technology and the large-pitch fiber design, which has enabled the stellar ascent of intense 1 µm fiber laser systems in the past decade. Bringing this approach to the mid-infrared opens up numerous opportunities for performance scaling such as exploiting the fiber design towards larger fiber dimensions and thus, higher nonlinear limits. Additionally, the broad gain bandwidth offered by thulium-doped fused silica allows for the direct amplification of sub-100 fs pulses, with the opportunity to access the few-cycle regime using straightforward and power-scalable post-compression schemes. These prospects in conjunction with the opportunity to investigate the fundamental wavelength dependency of mode-instabilities, one of the most limiting challenges for the power scaling of 1 µm fiber lasers, emphasize the potential behind this research project.

 

 

Marta Gilaberte

Marta Gilaberte

Fraunhofer Institute for Applied Optics and Precision Engineering IOF
Research Field: Quantum Technologies
Email:  
Phone: +49 3641-807361

Quantum enhanced imaging

One of the main tasks in imaging systems is to find an optimum trade-off between the available detector technology, the spectral range to investigate a certain sample, and the requirements on image quality like resolution and contrast. A short example illustrated the situation: Si-based detection technology is most common, but naturally is not feasible to detect in the far infrared or THz-regime. In addition, one cannot expect to have molecular resolution in these spectral ranges. Those restrictions can be circumvent by novel imaging approaches utilizing quantum properties of certain light fields.

In particular, quantum imaging based on induced coherence allows illuminating objects with quantum light of an appropriate wavelength, while performing the actual detection with quantum light of another wavelength, allowing optimum detection efficiency. The two beams of quantum light can be generated by non-degenerated spontaneous parametric down conversion.

 

 

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Maximilian Heck

Institute of Applied Physics (IAP), Friedrich Schiller University Jena
Research Field: Ultrafast optics
Email:
Phone: +49 3641-9-47822

Mode conversion and polarization control in advanced fibers by ultrashort pulse laser structuring

The control of light propagation inside optical fibers is essential for a broad variety of applications from sensing to high-power fiber lasers. In particular, special fibers like large mode area or microstructured fibers open possibilities far beyond standard single mode fibers. In order to locally tailor their guiding properties, a precisely defined structure is required. This can be realized by means of the strong nonlinear multi-photon interactions of femtosecond laser light for the structuring process. The femtosecond laser pulses offer a flexible approach to concentrate and pattern the refractive index profile anywhere within the core waveguide as well as outside in the cladding. This opens a vast field of yet untapped possibilities to realize modifications specifically adapted for the spatial properties of the guided light in the fiber.
The goal of the PhD project is to seamlessly integrate novel functionalities into advanced optical fibers. Thereby the project intends to pursue fundamental research related to ultrafast laser-matter interaction and develop new fiber inscription technologies for the modal control and mode conversion as well as approaches for polarization control in fiber waveguides.

 

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Ria Krämer

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Ultrafast optics
Email:
Phone: +49 3641-9-47824

Mode selective in-fiber components inscribed by ultrashort laser pulses

The aim of the PhD project is the development of integrated mode selective components for monolithic high power fiber lasers. Due to limitations of nonlinear effects caused by the high power density in the fiber core, commonly large mode are (LMA) fibers are applied. However, LMA fibers support not only the fundamental mode, but also higher order modes leading to mode instabilities and a degrading beam quality, requiring mode controlling elements. One essential component are fiber Bragg gratings (FBG), narrowband reflectors consisting of periodic refractive index modulations in the fiber core, which are used as resonator mirrors. The cross section of the refractive index modification influences the coupling of the guided modes – a large homogeneous modification can suppress coupling between the modes ensuring a stable laser performance. Additionally, a mode modulator is developed, enabling an energy transfer between the guided modes. It is based on additional refractive index modifications alongside the fiber core in the cladding, which lead to a disturbance of the guidance of the modes. Depending on the geometries of the modifications, different modal contents can be adressed. 

 

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Athira Kuppadakkath

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Nano Optics
Email:
Phone: +49 3641- 9-47989

 Investigations of Fluorescent 2D-Nanoparticles as for Applications as Guide Stars for Adaptive Imaging

Monolayer and few layer transition metal dichalcogenides exhibit interesting optical properties. Their fluorescence properties make them an interesting candidate to substitute for fluorescent dyes in some modes of fluorescence imaging, as it doesn't suffer from photo-bleaching and does not exhibit phototoxicity, as is known from fluorescent dyes. Among these is adaptive optical imaging, which works by correcting the distortion in waves that results from propagation of light through scattering medium. This technique takes correction information about the wavefront distortion from a fluorescent guidestar, and uses it to configure the adaptive optical element.  This project involves developing an adaptive optical imaging system and investigating fluorescent properties of 2d nanomaterials.

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Franz Löchner

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Nano Optics
Email: 
Phone: +49 3641-9-47568

 Dynamics of coupled nonlinear cavity systems

Optical resonators composed from micro- and nanostructures have the advantage to enhance the nonlinear photonic interaction processes by concentration of light. Additionally, one can control the polarization and emission direction by designing the resonator geometry.
Among many photonic nonlinear interactions which can be enhanced by such resonators, parametric frequency conversion is a versatile tool to create light with specific spectral properties, e.g. Second Harmonic Generation, or light of quantum nature, e.g. by Spontaneous Parametric Down-Conversion.
In this work, we experimentally and numerically study several geometries:
- Plasmonic and dielectric nanoantennas to enhance the second order nonlinearity of two-dimensional membranes, so called monolayers of transition metal dichalcogenides.
- Integrated optical structures like photonic crystal cavities and ring resonators in Lithium niobate (LiNbO3) to enhance and control Spontaneous Parametric Down-Conversion.

 

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Tilman Lühder

Leibniz Institute of Photonic Technology (IPHT)
Email:
Phone: +49 3641-206281

 Investigation of the plasmonic drag effect inside plasmonic fibers

Light detection is essential to most photonic systems in research and technology. Classical light detectors use the excitation of electrons to the conduction band of semiconductors or to free carriers (photoelectric effect). In this project a new, fast and compact detection method based on the plasmon drag effect will be investigated. Similar to the photon drag, electrons are accelerated by light, but here, the drag originates from surface plasmon polaritons (SPP), excited by the photons and leading to a macroscopic photocurrent. SPPs are electromagnetic waves confined to a metal-dielectric interface and connected to electron density oscillations. In the past, kretschmann configuration or gratings were used to excite SPPs, here, fibers based solutions in two different approaches are prefered. First, a tapered fiber coated with gold and, second, a gold microwire parallel to the optical core inside the fiber are fabricated using PAMF (pressure assisted melt filling), allowing a tuning to support SPPs of a wide wavelength range from 0,4 to 2 µm. The objective of this project is to understand the basic physics of this light-electrical junction dependent on temperature, resonance wavelength, interaction length, SPP mode order, fiber and metal geometry and to evaluate applications in in-fiber sensing and optical circuitry.

 

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Kay Schaarschmidt

Leibniz Institute of Photonic Technologies (IPHT), Friedrich Schiller University Jena
Research Field: Fiber sensors
Email: 
Phone: +49 3641-206219

Light Generation in Nonlinear Liquid-Core-Fibers

Nonlinear phenomena in fibers had been studied extensively in the past decades. Sophisticated structures allowing for strong light confinement in both solid core and hollow core fibers were utilized to generate new frequencies based on the optical Kerr effect in either glass or gasses. However, in liquid-core-fibers filled with e.g. Carbon disulfide a much larger nonlinear refractive index than in silica based fibers is available. Designing the fiber structure and exploiting the liquids response to temperature and pressure enable dispersion tuning for both, efficient harmonic generation and soliton driven supercontinuum generation. In the latter case, rotational degrees of freedom of the molecules in the liquid lead to significant non-instantaneous molecular response if the pulse duration is chosen accordingly. Continua generated in such hybrid fibers are much less susceptible to noise and are a promising concept for future coherent broadband sources. 

 

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Evgeny Shestaev

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email: 
Phone: +49 3641-9-47642

 Carrier-envelope phase stability of high-power few-cycle fiber lasers

 

Rudru

Rudrakant Sollapur

Institute of Optics and Quantum Electronics, Friedrich Schiller University Jena
Research Field: Ultrafast Optics / Quantum Electronics
Email: 
Phone: +49 3641-9-47235

Nonlinear optics in hollow core fibers: generation of broadband supercontinuum sources from ultraviolet to mid-infrared wavelength

The interaction of intense laser pulses with matter is a vivid research area as it not only aims at investigating fundamental physical questions but also offers a variety of applications. The interaction of atomic and molecular gases with ultrashort infrared laser pulses generates new frequencies due to nonlinear effects. The central idea of this project is to study supercontinuum generation in gas filled anti-resonant hollow-core fiber (ARHCF), which enables efficient guiding of intense light. Different ARHCF features transmission windows between deep ultraviolet and mid infrared for single mode operation.
It is possible to selectively enhance the spectral output due to nonlinear effects by choice of gaseous nonlinear medium, pressure of the gas and fiber design. In perspective, these developments may lead to a new class of ultracompact high energy supercontinuum sources from ultraviolet to mid-infrared wavelengths, with applicability in spectroscopy, microscopy, metrology and biophotonics..

 

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Christoph Stihler

Institute of Applied Physics, Friedrich Schiller University Jena
Research Field: Fiber and waveguide lasers
Email: 
Phone: +49 3641-9-47819

Mitigation of Transverse Mode Instabilities in High-Power Fiber Laser Systems

The exponential evolution of the average output power of fiber laser systems with nearly diffraction-limited beam quality came to a sudden stop around 2009 when the effect of Transverse Mode Instabilities (TMI) was discovered. TMI is related to a thermally inscribed refractive index grating along the fiber, which enables a dynamic energy coupling between different transverse modes. Thus, the beam quality and stability is significantly decreased once that a certain average power threshold has been reached.

The aim of this project is to develop strategies to mitigate TMI. The overall approach is to wash out the refractive index grating along the fiber. Hence, the coupling between the modes is decreased. One technique developed in the scope of this project is the so‑called pump modulation which has already been successfully demonstrated. By modulating the pump power with an appropriate frequency, we have been able to achieve a significant improvement in beam stability and beam quality up to an average output power two times above the TMI threshold. This shows that further improvements in this technique and the development of new mitigation strategies could pave the way for a further average output power scaling of fiber laser systems with nearly diffraction-limited beam quality.

 

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Martin Wimmer

Institute of Condensed Matter Theory and Solid State Optics (IFTO) , Friedrich Schiller University Jena
Research Field: Quantum Random Walks in discrete fiber networks
Email: 
Phone: +49 3641-9-47179

Linear and nonlinear light propagation through optical mesh lattices

Based on a time-multiplexing setup consisting of two fiber loops of different length, light propagation through a temporally and spatially discretized mesh lattice is studied. In the linear regime, Bloch oscillations are induced by applying a phase gradient analogue to an electrical field in a solid state. In a very intriguing way, these oscillations are used for a tomography of the complex band structure of a dissipative system. By meticulously balancing gain and loss and an additional phase modulation, a so-called parity-time symmetry is established, where nonlinear localization and solitons are observed. In the nonlinear regime, the analogy between the nonlinear Schrödinger equation and the Gross-Pitaevskii equation forecast a superfluid mobility of light, which is successfully observed in experiments. Furthermore, echo-like phenomena are studied in these mesh lattices, that are related to the field of time reversal. Finally, the influence of the Berry curvature on light propagation through the lattice is also a topic of my research.

 

Postdoctoral scientists

Alessandro Alberucci

Alessandro Alberucci

Institute of Applied Physics (IAP), Friedrich Schiller University Jena
Research Field: Ultrafast optics
Email:
Phone: +49 3641-9-47987

Optical waveguides based upon the Pancharatnam-Berry phase

The aim of this project is the theoretical and experimental investigation of a new kind of optical waveguiding based upon the Pancharatnam-Berry phase, a geometric phase arising from polarization variations. Whereas standard waveguides are based upon local changes in the refractive index of the material, the proposed mechanism requires the local rotation of an anisotropic material. Experimentally, realization of these waveguides using femtosecond-laser writing in glasses and other dielectrics will be explored. Other possible implementations will be considered as well, including metamaterials and soft-matter. The proposed guiding mechanism minimizes the intramodal dispersion, a relevant property with respect to optical communications and nonlinear optical effects, such as second harmonic generation. Furthermore, the optical modes in these guides feature a complex polarization distribution, i.e., they are structured beams. Thus, waveguiding supported by the Pancharatnam-Berry phase represents a whole new platform for the realization of new demultiplexing protocols, both in the classical and quantum regimes.

 

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