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- ItemLow-temperature atmospheric pressure plasma conversion of polydimethylsiloxane and polysilazane precursor layers to oxide thin films(Weinheim : Wiley VCH, 2023) Rudolph, Martin; Birtel, Peter; Arnold, Thomas; Prager, Andrea; Naumov, Sergej; Helmstedt, Ulrike; Anders, André; With, Patrick C.We study the conversion of two polymeric silicon precursor compound layers (perhydropolysilazane and polydimethylsiloxane) on a silicon wafer and polyethylene terephthalate substrates to silicon oxide thin films using a pulsed atmospheric pressure plasma jet. Varying the scan velocity and the number of treatments results in various film compositions, as determined by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The mechanism suggested for the conversion process includes the decomposition of the precursor triggered by plasma-produced species, the oxidation of the surface, and finally, the diffusion of oxygen into the film, while gases produced during the precursor decomposition diffuse out of the film. The latter process is possibly facilitated by local plasma heating of the surface. The precursor conversion appears to depend sensitively on the balance between the different contributions to the conversion mechanism.
- ItemDiode-Pumped Laser Operation of Tb3+:LiLuF4 in the Green and Yellow Spectral Range(Weinheim : Wiley VCH, 2020) Castellano-Hernández, Elena; Kalusniak, Sascha; Metz, Philip W.; Kränkel, ChristianHere, a diode-pumped laser based on trivalent terbium (Tb3+) as the active ion is reported. Optical pumping of a Tb3+-doped lithium-lutetium-fluoride (LiLuF4) crystal with up to 200 mW from a diode laser emitting at a wavelength of 488.2 nm enables continuous-wave lasing directly in the green and in the yellow. At an emission wavelength of 542 nm, the laser reaches an output power of up to 43.8 mW with a high slope efficiency of 52% with respect to the absorbed pump power. The yellow laser at 587 nm exhibits a slope efficiency of 22% and the output power of 13.8 mW is only limited by the available pump power. Laser thresholds as low as 14 and 27 mW of absorbed pump power are observed for the green and yellow, respectively. The investigations toward further optimization of the laser performance reveal that highly Tb3+-doped materials are suitable for compact, efficient, and affordable diode-pumped solid-state lasers with direct emission in the visible spectral range. These results are of high relevance, as in particular for the yellow spectral range such systems are currently not available. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemResonance-Induced Dispersion Tuning for Tailoring Nonsolitonic Radiation via Nanofilms in Exposed Core Fibers(Weinheim : Wiley VCH, 2020) Lühder, Tilman A.K.; Schaarschmidt, Kay; Goerke, Sebastian; Schartner, Erik P.; Ebendorff-Heidepriem, Heike; Schmidt, Markus A.Efficient supercontinuum generation demands for fine-tuning of the dispersion of the underlying waveguide. Resonances introduced into waveguide systems can substantially improve nonlinear dynamics in ultrafast supercontinuum generation via modal hybridization and formation of avoided crossings. Using the example of exposed core fibers functionalized by nanofilms with sub-nanometer precision both zero-dispersion and dispersive wave emission wavelengths are shifted by 227 and 300 nm, respectively, at tuning slopes higher than 20 nm/nm. The presented concept relies on dispersion management via induced resonances and can be straightforwardly extended to other deposition techniques and film geometries such as multilayers or 2D materials. It allows for the creation of unique dispersion landscapes, thus tailoring nonlinear dynamics and emission wavelengths and for making otherwise unsuitable waveguides relevant for ultrafast nonlinear photonics. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemFemtosecond Field‐Driven On‐Chip Unidirectional Electronic Currents in Nonadiabatic Tunneling Regime(Weinheim : Wiley VCH, 2021) Shi, Liping; Babushkin, Ihar; Husakou, Anton; Melchert, Oliver; Frank, Bettina; Yi, Juemin; Wetzel, Gustav; Demircan, Ayhan; Lienau, Christoph; Giessen, Harald; Ivanov, Misha; Morgner, Uwe; Kovacev, MilutinRecently, asymmetric plasmonic nanojunctions have shown promise as on-chip electronic devices to convert femtosecond optical pulses to current bursts, with a bandwidth of multi-terahertz scale, although yet at low temperatures and pressures. Such nanoscale devices are of great interest for novel ultrafast electronics and opto-electronic applications. Here, the device is operated in air and at room temperature, revealing the mechanisms of photoemission from plasmonic nanojunctions, and the fundamental limitations on the speed of optical-to-electronic conversion. Inter-cycle interference of coherent electronic wavepackets results in a complex energy electron distribution and birth of multiphoton effects. This energy structure, as well as reshaping of the wavepackets during their propagation from one tip to the other, determine the ultrafast dynamics of the current. It is shown that, up to some level of approximation, the electron flight time is well-determined by the mean ponderomotive velocity in the driving field.
- ItemTaming Ultrafast Laser Filaments for Optimized Semiconductor–Metal Welding(Weinheim : Wiley VCH, 2021) Chambonneau, Maxime; Li, Qingfeng; Fedorov, Vladimir Yu.; Blothe, Markus; Schaarschmidt, Kay; Lorenz, Martin; Tzortzakis, Stelios; Nolte, StefanUltrafast laser welding is a fast, clean, and contactless technique for joining a broad range of materials. Nevertheless, this technique cannot be applied for bonding semiconductors and metals. By investigating the nonlinear propagation of picosecond laser pulses in silicon, it is elucidated how the evolution of filaments during propagation prevents the energy deposition at the semiconductor–metal interface. While the restrictions imposed by nonlinear propagation effects in semiconductors usually inhibit countless applications, the possibility to perform semiconductor–metal ultrafast laser welding is demonstrated. This technique relies on the determination and the precompensation of the nonlinear focal shift for relocating filaments and thus optimizing the energy deposition at the interface between the materials. The resulting welds show remarkable shear joining strengths (up to 2.2 MPa) compatible with applications in microelectronics. Material analyses shed light on the physical mechanisms involved during the interaction. © 2020 The Authors. Laser & Photonics Reviews published by Wiley-VCH GmbH
- ItemNumerical and Experimental Demonstration of Intermodal Dispersive Wave Generation(Weinheim : Wiley VCH, 2021) Lüpken, Niklas M.; Timmerkamp, Maximilian; Scheibinger, Ramona; Schaarschmidt, Kay; Schmidt, Markus A.; Boller, Klaus‐J.; Fallnich, CarstenEvidence of intermodal dispersive wave generation mediated by intermodal cross-phase modulation (iXPM) between different transverse modes during supercontinuum generation in silicon nitride waveguides is presented. The formation of a higher-order soliton in one strong transverse mode leads to phase modulation of a second, weak transverse mode by iXPM. The phase modulation enables not only supercontinuum generation but also dispersive wave generation within the weak mode, that otherwise has insufficient power to facilitate dispersive wave formation. The nonlinear frequency conversion scheme presented here suggests phase-matching conditions beyond what is currently known, which can be exploited for extending the spectral bandwidth within supercontinuum generation.
- ItemOptical Vernier Effect: Recent Advances and Developments(Weinheim : Wiley VCH, 2021) Gomes, André D.; Bartelt, Hartmut; Frazão, OrlandoThe optical analog of the Vernier effect applied to fiber interferometers is a recent tool to enhance the sensitivity and resolution of optical fiber sensors. This effect relies on the overlap between the signals of two interferometers with slightly detuned interference frequencies. The Vernier envelope modulation generated at the output spectrum presents magnified sensing capabilities (i.e., magnified wavelength shift) compared to that of the individual sensing interferometers that constitute the system, leading to a new generation of highly sensitive fiber sensing devices. This review analyses the recent advances and developments of the optical Vernier effect from a fiber sensing point-of-view. Initially, the fundamentals of the effect are introduced, followed by an extensive review on the state-of-the-art, presenting all the different configurations and types of fiber sensing interferometers used to introduce the optical Vernier effect. This paper also includes an overview of the complex case of enhanced Vernier effect and the introduction of harmonics to the effect.