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- ItemHybrid Optical Fibers – An Innovative Platform for In‐Fiber Photonic Devices(Weinheim : Wiley-VCH, 2015) Alexander Schmidt, Markus; Argyros, Alexander; Sorin, FabienThe field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.
- ItemA general approach for all-visible-light switching of diarylethenes through triplet sensitization using semiconducting nanocrystals(London [u.a.] : RSC, 2022) Hou, Lili; Larsson, Wera; Hecht, Stefan; Andréasson, Joakim; Albinsson, BoCoupling semiconducting nanocrystals (NCs) with organic molecules provides an efficient route to generate and transfer triplet excitons. These excitons can be used to power photochemical transformations such as photoisomerization reactions using low energy radiation. Thus, it is desirable to develop a general approach that can efficiently be used to control photoswitches using all-visible-light aiming at future applications in life- and materials sciences. Here, we demonstrate a simple ‘cocktail’ strategy that can achieve all-visible-light switchable diarylethenes (DAEs) through triplet energy transfer from the hybrid of CdS NCs and phenanthrene-3-carboxylic acid, with high photoisomerization efficiency and improved fatigue resistance. The size-tunable excitation energies of CdS NCs make it possible to precisely match the clear spectral window of the relevant DAE photoswitch. We demonstrate reversible all-visible-light photoisomerization of a series of DAE derivatives both in the liquid and solid state, even in the presence of oxygen. Our general strategy is promising for fabrication of all-visible-light activated optoelectronic devices as well as memories, and should in principle be adaptable to photopharmacology.
- ItemSubwavelength population density gratings in resonant medium created by few-cycle pulses(Bristol : IOP Publ., 2017) Arkhipov, R.M.; Arkhipov, M.V.; Pakhomov, A.V.; Babushkin, I.; Demircan, A.; Morgner, U.; Rosanov, N.N.We consider theoretically recently proposed a new possibility of creation, erasing and ultrafast control of population density grating. Such grating can be created in resonant medium when ultrashort pulses with duration smaller than relaxation times in the resonant medium (coherent light matter interactions) propagate without overlapping in this medium. Possible applications in the ultrafast optics such as optical switcher and laser beam deflector are discussed.
- ItemFrom atomistic tight-binding theory to macroscale drift–diffusion: Multiscale modeling and numerical simulation of uni-polar charge transport in (In,Ga)N devices with random fluctuations(Melville, NY : American Inst. of Physics, 2021) O’Donovan, Michael; Chaudhuri, Debapriya; Streckenbach, Timo; Farrell, Patricio; Schulz, Stefan; Koprucki, ThomasRandom alloy fluctuations significantly affect the electronic, optical, and transport properties of (In,Ga)N-based optoelectronic devices. Transport calculations accounting for alloy fluctuations currently use a combination of modified continuum-based models, which neglect to a large extent atomistic effects. In this work, we present a model that bridges the gap between atomistic theory and macroscopic transport models. To do so, we combine atomistic tight-binding theory and continuum-based drift–diffusion solvers, where quantum corrections are included via the localization landscape method. We outline the ingredients of this framework in detail and present first results for uni-polar electron transport in single and multi- (In,Ga)N quantum well systems. Overall, our results reveal that both random alloy fluctuations and quantum corrections significantly affect the current–voltage characteristics of uni-polar electron transport in such devices. However, our investigations indicate that the importance of quantum corrections and random alloy fluctuations can be different for single and multi-quantum well systems.
- ItemTowards a life-time-limited 8-octave-infrared photoconductive germanium detector(Bristol : IOP Publ., 2015) Pavlov, S.G.; Deßmann, N.; Pohl, A.; Abrosimov, N.V.; Mittendorff, M.; Winnerl, S.; Zhukavin, R.K; Tsyplenkov, V.V.; Shengurov, D.V.; Shastin, V.N.; Hübers, H.-W.Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times.
- ItemThe new ultra high-speed all-optical coherent streak-camera(Bristol : IOP Publ., 2015) Arkhipov, R.M.; Arkhipov, M.V.; Egorov, V.S.; Chekhonin, I.A.; Chekhonin, M.A.; Bagayev, S.N.In the present paper a new type of ultra high-speed all-optical coherent streak-camera was developed. It was shown that a thin resonant film (quantum dots or molecules) could radiate the angular sequence of delayed ultra-short pulses if a transverse spatial periodic distribution of the laser pump field amplitude has a triangle shape.
- ItemTerahertz emission from lithium doped silicon under continuous wave interband optical excitation(Bristol : IOP Publ., 2015) Andrianov, A.V.; Zakhar'in, A.O.; Zhukavin, R.K.; Shastin, V.N.; Abrosimov, N.V.We report on experimental observation and study of terahertz emission from lithium doped silicon crystals under continuous wave band-to-band optical excitation. It is shown that radiative transitions of electrons from 2P excited states of lithium donor to the 1S(A1) donor ground state prevail in the emission spectrum. The terahertz emission occurs due to capture of nonequilibrium electrons to charged donors, which in turn are generated in the crystal as a result of impurity assisted electron-hole recombination. Besides the intracentre radiative transitions the terahertz emission spectrum exhibits also features at about 12.7 and 15.27 meV, which could be related to intraexciton transitions and transitions from the continuum to the free exciton ground state.
- ItemSelective area growth of AlGaN nanopyramid arrays on graphene by metal-organic vapor phase epitaxy(Melville, NY : American Inst. of Physics, 2018) Munshi, A. Mazid; Kim, Dong-Chul; Heimdal, Carl Philip; Heilmann, Martin; Christiansen, Silke H.; Vullum, Per Erik; van Helvoort, Antonius T. J.; Weman, HelgeWide-bandgap group III-nitride semiconductors are of special interest for applications in ultraviolet light emitting diodes, photodetectors, and lasers. However, epitaxial growth of high-quality III-nitride semiconductors on conventional single-crystalline substrates is challenging due to the lattice mismatch and differences in the thermal expansion coefficients. Recently, it has been shown that graphene, a two-dimensional material, can be used as a substrate for growing high-quality III-V semiconductors via quasi-van der Waals epitaxy and overcome the named challenges. Here, we report selective area growth of AlGaN nanopyramids on hole mask patterned single-layer graphene using metal-organic vapor phase epitaxy. The nanopyramid bases have a hexagonal shape with a very high nucleation yield. After subsequent AlGaN/GaN/AlGaN overgrowth on the six {10 (1) over bar1} semi-polar side facets of the nanopyramids, intense room-temperature cathodoluminescence emission is observed at 365 nm with whispering gallery-like modes. This work opens up a route for achieving III-nitride opto-electronic devices on graphene substrates in the ultraviolet region for future applications.
- ItemPhase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties(Washington, DC : ACS, 2021) Martín-García, Beatriz; Spirito, Davide; Biffi, Giulia; Artyukhin, Sergey; Francesco Bonaccorso, null; Krahne, RomanHalide double perovskites are an interesting alternative to Pb-containing counterparts as active materials in optoelectronic devices. Low-dimensional double perovskites are fabricated by introducing large organic cations, resulting in organic/inorganic architectures with one or more inorganic octahedra layers separated by organic cations. Here, we synthesized layered double perovskites based on 3D Cs2AgBiBr6, consisting of double (2L) or single (1L) inorganic octahedra layers, using ammonium cations of different sizes and chemical structures. Temperature-dependent Raman spectroscopy revealed phase transition signatures in both inorganic lattice and organic moieties by detecting variations in their vibrational modes. Changes in the conformational arrangement of the organic cations to an ordered state coincided with a phase transition in the 1L systems with the shortest ammonium moieties. Significant changes of photoluminescence intensity observed around the transition temperature suggest that optical properties may be affected by the octahedral tilts emerging at the phase transition.