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- ItemMulti-millijoule, few-cycle 5 µm OPCPA at 1 kHz repetition rate(Washington, DC : Soc., 2020) von Grafenstein, Lorenz; Bock, Martin; Ueberschaer, Dennis; Escoto, Esmerando; Koç, Azize; Zawilski, Kevin; Schunemann, Peter; Griebner, Uwe; Elsaesser, ThomasA table-top midwave-infrared optical parametric chirped pulse amplification (OPCPA) system generates few-cycle pulses with multi-10 GW peak power at a 1 kHz repetition rate. The all-optically synchronized system utilizes ZnGeP2 nonlinear crystals and a highly stable 2 µm picosecond pump laser based on Ho:YLiF4. An excellent energy extraction is achieved by reusing the pump pulse after the third parametric power amplification stage, resulting in 3.4 mJ idler pulses at a center wavelength of 4.9 µm. Pulses as short as 89.4 fs are achieved, close to only five optical cycles. Taking into account the pulse energy, a record high peak power of 33 GW for high-energy mid-IR OPCPAs beyond 4 µm wavelength is demonstrated. © 2020 OSA - The Optical Society. All rights reserved.
- ItemTerahertz absorption-saturation and emission from electron-doped germanium quantum wells(Washington, DC : Soc., 2020) Ciano, Chiara; Virgilio, Michele; Bagolini, Luigi; Baldassarre, Leonetta; Pashkin, Alexej; Helm, Manfred; Montanari, Michele; Persichetti, Luca; Di Gaspare, Luciana; Capellini, Giovanni; Paul, Douglas J.; Scalari, Giacomo; Faist, Jèrome; De Seta, Monica; Ortolani, MicheleWe study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1→3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model. In the emission spectroscopy experiment, we observed a photoluminescence peak at 4 THz, which can be attributed to the 3→2 intersubband transition with possible contribution from the 2→1 intersubband transition. These results represent a step towards silicon-based integrated terahertz emitters.
- ItemEnabling time-resolved 2D spatial-coherence measurements using the Fourier-analysis method with an integrated curved-grating beam monitor(Washington, DC : Soc., 2020) Bagschik, Kai; Schneider, Michael; Wagner, Jochen; Buss, Ralph; Riepp, Matthias; Philippi-Kobs, Andre; Müller, Leonard; Roseker, Wojciech; Trinter, Florian; Hoesch, Moritz; Viefhaus, Jens; Eisebitt, Stefan; Grübel, Gerhard; Oepen, Hans Peter; Frömter, RobertDirect 2D spatial-coherence measurements are increasingly gaining importance at synchrotron beamlines, especially due to present and future upgrades of synchrotron facilities to diffraction-limited storage rings. We present a method to determine the 2D spatial coherence of synchrotron radiation in a direct and particularly simple way by using the Fourier-analysis method in conjunction with curved gratings. Direct photon-beam monitoring provided by a curved grating circumvents the otherwise necessary separate determination of the illuminating intensity distribution required for the Fourier-analysis method. Hence, combining these two methods allows for time-resolved spatial-coherence measurements. As a consequence, spatial-coherence degradation effects caused by beamline optics vibrations, which is one of the key issues of state-of-the-art X-ray imaging and scattering beamlines, can be identified and analyzed. © 2020 Optical Society of America.
- Item2 MW peak power generation in fluorine co-doped Yb fiber prepared by powder-sinter technology(Washington, DC : Soc., 2020) Leich, Martin; Kalide, André; Eschrich, Tina; Lorenz, Adrian; Lorenz, Martin; Wondraczek, Katrin; Schönfeld, Dörte; Langner, Andreas; Schötz, Gerhard; Jäger, MatthiasWe report on the first, to the best of our knowledge, implementation of a fluorine co-doped large-mode-area REPUSIL fiber for high peak power amplification in an ultrashort-pulse master oscillator power amplifier. The core material of the investigated step-index fiber with high Yb-doping level, 52 µm core and high core-to-clad ratio of 1:4.2 was fabricated by means of the REPUSIL powder-sinter technology. The core numerical aperture was adjusted by fluorine codoping to 0.088. For achieving high beam quality and for ensuring a monolithic seed path, the LMA fiber is locally tapered. We demonstrate an Yb fiber amplifier with near-diffraction-limited beam quality of M2 = 1.3, which remains constant up to a peak power of 2 MW. This is a record for a tapered single core fiber. © 2020 Optical Society of America
- Item27 W 2.1 µm OPCPA system for coherent soft X-ray generation operating at 10 kHz(Washington, DC : Soc., 2020) Feng, Tianli; Heilmann, Anke; Bock, Martin; Ehrentraut, Lutz; Witting, Tobias; Yu, Haohai; Stiel, Holger; Eisebitt, Stefan; Schnürer, MatthiasWe developed a high power optical parametric chirped-pulse amplification (OPCPA) system at 2.1 µm harnessing a 500 W Yb:YAG thin disk laser as the only pump and signal generation source. The OPCPA system operates at 10 kHz with a single pulse energy of up to 2.7 mJ and pulse duration of 30 fs. The maximum average output power of 27 W sets a new record for an OPCPA system in the 2 µm wavelength region. The soft X-ray continuum generated through high harmonic generation with this driver laser can extend to around 0.55 keV, thus covering the entire water window (284 eV - 543 eV). With a repetition rate still enabling pump-probe experiments on solid samples, the system can be used for many applications. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
- ItemImportance of substrates for the visibility of "dark" plasmonic modes(Washington, DC : Soc., 2020) Fiedler, Saskia; Raza, Søren; Ai, Ruoqi; Wang, Jianfang; Busch, Kurt; Stenger, Nicolas; Mortensen, N. Asger; Wolff, ChristianDark plasmonic modes have interesting properties, including longer lifetimes and narrower linewidths than their radiative counterpart, and little to no radiative losses. However, they have not been extensively studied yet due to their optical inaccessibility. In this work, we systematically investigated the dark radial breathing modes (RBMs) in monocrystalline gold nanodisks, specifically their outcoupling behavior into the far-field by cathodoluminescence spectroscopy. Increasing the substrate thickness resulted in an up to 4-fold enhanced visibility. This is attributed to breaking the mirror symmetry by the high-index substrate, creating an effective dipole moment. Furthermore, the resonance energy of the dark RMBs can be easily tuned by varying the nanodisk diameter, making them promising candidates for nanophotonic applications. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
- ItemThin-disk laser-pumped OPCPA system delivering 4.4 TW few-cycle pulses(Washington, DC : Soc., 2020) Kretschmar, Martin; Tuemmler, Johannes; Schütte, Bernd; Hoffmann, Andreas; Senfftleben, Björn; Mero, Mark; Sauppe, Mario; Rupp, Daniela; Vrakking, Marc J.J.; Will, Ingo; Nagy, TamasWe present an optical parametric chirped pulse amplification (OPCPA) system delivering 4.4 TW pulses centered at 810 nm with a sub-9 fs duration and a carrier-envelope phase stability of 350 mrad. The OPCPA setup pumped by sub-10 ps pulses from two Yb:YAG thin-disk lasers at 100 Hz repetition rate is optimized for a high conversion-efficiency. The terawatt pulses of the OPCPA are utilized for generating intense extreme ultraviolet (XUV) pulses by high-order harmonic generation, achieving XUV pulse energies approaching the microjoule level. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
- ItemDeep learning as phase retrieval tool for CARS spectra(Washington, DC : Soc., 2020) Houhou, Rola; Barman, Parijat; Schmitt, Micheal; Meyer, Tobias; Popp, Juergen; Bocklitz, ThomasFinding efficient and reliable methods for the extraction of the phase in optical measurements is challenging and has been widely investigated. Although sophisticated optical settings, e.g. holography, measure directly the phase, the use of algorithmic methods has gained attention due to its efficiency, fast calculation and easy setup requirements. We investigated three phase retrieval methods: the maximum entropy technique (MEM), the Kramers-Kronig relation (KK), and for the first time deep learning using the Long Short-Term Memory network (LSTM). LSTM shows superior results for the phase retrieval problem of coherent anti-Stokes Raman spectra in comparison to MEM and KK. © 2020 OSA - The Optical Society. All rights reserved.
- ItemPerformance limits of astronomical arrayed waveguide gratings on a silica platform(Washington, DC : Soc., 2020) Stoll, Andreas; Madhav, Kalaga; Roth, MartinWe present a numerical and experimental study of the impact of phase errors on the performance of large, high-resolution arrayed waveguide gratings (AWG) for applications in astronomy. We use a scalar diffraction model to study the transmission spectrum of an AWG under random variations of the optical waveguide lengths. We simulate phase error correction by numerically trimming the lengths of the optical waveguides to the nearest integer multiple of the central wavelength. The optical length error distribution of a custom-fabricated silica AWG is measured using frequency-domain interferometry and Monte-Carlo fitting of interferogram intensities. In the end, we give an estimate for the phase-error limited size of a waveguide array manufactured using state-of-the-art technology. We show that post-processing eliminates phase errors as a performance limiting factor for astronomical spectroscopy in the H-band.
- ItemNanofiber-based high-Q microresonator for cryogenic applications(Washington, DC : Soc., 2020) Hütner, Johanna; Hoinkes, Thomas; Becker, Martin; Rothhardt, Manfred; Rauschenbeute, Arno; Skoff, Sarah M.We demonstrate a cryo-compatible, fully fiber-integrated, alignment-free optical microresonator. The compatibility with low temperatures expands its possible applications to the wide field of solid-state quantum optics, where a cryogenic environment is often a requirement. At a temperature of 4.6 K we obtain a quality factor of (9.9 ± 0.7) × 106. In conjunction with the small mode volume provided by the nanofiber, this cavity can be either used in the coherent dynamics or the fast cavity regime, where it can provide a Purcell factor of up to 15. Our resonator is therefore suitable for significantly enhancing the coupling between light and a large variety of different quantum emitters and due to its proven performance over a wide temperature range, also lends itself for the implementation of quantum hybrid systems. © 2020 OSA - The Optical Society. All rights reserved.