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- ItemGraphene Q-switched Yb:KYW planar waveguide laser(New York, NY : American Inst. of Physics, 2015) Kim, Jun Wan; Young Choi, Sun; Aravazhi, Shanmugam; Pollnau, Markus; Griebner, Uwe; Petrov, Valentin; Bae, Sukang; Jun Ahn, Kwang; Yeom, Dong-Il; Rotermund, FabianA diode-pumped Yb:KYW planar waveguide laser, single-mode Q-switched by evanescent-field interaction with graphene, is demonstrated for the first time. Few-layer graphene grown by chemical vapor deposition is transferred onto the top of a guiding layer, which initiates stable Q-switched operation in a 2.4-cm-long waveguide laser operating near 1027 nm. Average output powers up to 34 mW and pulse durations as short as 349 ns are achieved. The measured output beam profile, clearly exhibiting a single mode, agrees well with the theoretically calculated mode intensity distribution inside the waveguide. As the pump power is increased, the repetition rate and pulse energy increase from 191 to 607 kHz and from 7.4 to 58.6 nJ, respectively, whereas the pulse duration decreases from 2.09 μs to 349 ns.
- ItemPhotoluminescence lineshape of ZnO(New York, NY : American Inst. of Physics, 2014) Ullrich, B.; Singh, A.K.; Bhowmick, M.; Barik, P.; Ariza-Flores, D.; Xi, H.; Tomm, J.W.The merger of the absorption coefficient dispersion, retrieved from transmission by the modified Urbach rule introduced by Ullrich and Bouchenaki [Jpn. J. Appl. Phys. 30, L1285, 1991], with the extended Roosbroeck-Shockley relation reveals that the optical absorption in ZnO distinctively determines the photoluminescence lineshape. Additionally, the ab initio principles employed enable the accurate determination of the carrier lifetime without further specific probing techniques.
- ItemInfrared spectroscopy in superfluid helium droplets(Abingdon : Taylor and Francis Ltd., 2019) Verma D.; Tanyag R.M.P.; O’Connell S.M.O.; Vilesov A.F.For more than two decades, encapsulation in superfluid helium nanodroplets has served as a reliable technique for probing the structure and dynamics of molecules and clusters at a low temperature of ≈0.37 K. Due to weak interactions between molecules and the host liquid helium, good spectral resolution can usually be achieved, making helium droplets an ideal matrix for spectroscopy in a wide spectral range from infrared to ultraviolet. Furthermore, rotational structure in the spectra of small molecules provides a unique probe for interactions with the superfluid on an atomic scale. This review presents a summary of results and a discussion of recent experimental developments in helium droplet spectroscopy with the emphasis laid on infrared studies. Initially, studies focused on single molecules and have been expanded to larger species, such as metal-molecular clusters, biomolecules, free radicals, ions, and proteins. © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
- ItemBosonic spectral function and the electron-phonon interaction in HTSC cuprates(New York : Hindawi Publishing Corporation, 2010) Maksimov, E.G.; Kulić, M.L.; Dolgov, O.V.In this paper we discuss experimental evidence related to the structure and origin of the bosonic spectral function α2 F(ω) in high-temperature superconducting (HTSC) cuprates at and near optimal doping. Global properties of α2 F(ω), such as number and positions of peaks, are extracted by combining optics, neutron scattering, ARPES and tunnelling measurements. These methods give evidence for strong electron-phonon interaction (EPI) with 1<λep3.5 in cuprates near optimal doping. We clarify how these results are in favor of the modified Migdal-Eliashberg (ME) theory for HTSC cuprates near optimal doping. In Section 2 we discuss theoretical ingredientssuch as strong EPI, strong correlationswhich are necessary to explain the mechanism of d-wave pairing in optimally doped cuprates. These comprise the ME theory for EPI in strongly correlated systems which give rise to the forward scattering peak. The latter is supported by the long-range part of EPI due to the weakly screened Madelung interaction in the ionic-metallic structure of layered HTSC cuprates. In this approach EPI is responsible for the strength of pairing while the residual Coulomb interaction and spin fluctuations trigger the d-wave pairing. Copyright © 2010 E. G. Maksimov et al.
- ItemNear-field dynamics of broad area diode laser at very high pump levels(New York, NY : American Inst. of Physics, 2011) Hempel, M.; Tomm, J.W.; Baeumler, M.; Konstanzer, H.; Mukherjee, J.; Elsaesser, T.Near-field properties of the emission of broad area semiconductor diode lasers under extremely high pumping of up to ∼50 times the threshold are investigated. A transition from a gain to thermally-induced index guiding is shown under operation with single pulses of 300 ns duration. At highest output powers, catastrophic optical damage is observed which is studied in conjunction with the evolution of time-averaged filamentary near-field properties. Dynamics of the process is resolved on a picosecond time scale.
- ItemDynamical studies on the generation of periodic surface structures by femtosecond laser pulses(Les Ulis : EDP Sciences, 2013) Rosenfeld, A.; Höhm, S.; Bonse, J.; Krüger, J.The dynamics of the formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800 nm center wavelength) is studied experimentally using a double pulse experiment with cross polarized pulse sequences and a trans illumination femtosecond time-resolved (0.1 ps - 1 ns) pump-probe diffraction approach. The results in both experiments confirm the importance of the ultrafast energy deposition and the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.
- ItemScanning single quantum emitter fluorescence lifetime imaging: Quantitative analysis of the local density of photonic states(Washington, DC : American Chemical Society, 2014) Schell, A.W.; Engel, P.; Werra, J.F.M.; Wolff, C.; Busch, K.; Benson, O.Their intrinsic properties render single quantum systems as ideal tools for quantum enhanced sensing and microscopy. As an additional benefit, their size is typically on an atomic scale that enables sensing with very high spatial resolution. Here, we report on utilizing a single nitrogen vacancy center in nanodiamond for performing three-dimensional scanning-probe fluorescence lifetime imaging microscopy. By measuring changes of the single emitter's lifetime, information on the local density of optical states is acquired at the nanoscale. Three-dimensional ab initio discontinuous Galerkin time-domain simulations are used in order to verify the results and to obtain additional insights. This combination of experiment and simulations to gather quantitative information on the local density of optical states is of direct relevance for the understanding of fundamental quantum optical processes as well as for the engineering of novel photonic and plasmonic devices.
- ItemExcitation of H2 at large internuclear separation: F1∑+g outer well states and continuum resonances(London : Taylor & Francis, 2019) Trivikram, T.M.; Salumbides, E.J.; Jungen, Ch.; Ubachs, W.Bound and free quantum resonances of molecular hydrogen exhibiting wave-function density at large internuclear separation, (Formula presented.) 4–5 a.u., are excited via multi-step laser spectroscopy. Highly excited vibrational levels of H (Formula presented.) are prepared via two-photon UV-photolysis of H (Formula presented.) S. Subsequent two-photon Doppler-free precision measurements are performed connecting (Formula presented.) levels with (Formula presented.) outer-well levels. Detection and spectroscopic labelling of the quantum states is assisted by further laser excitation into the auto-ionisation continuum employing a third UV-laser. Level energies of high rotational states ((Formula presented.)) in the outer-well state (Formula presented.) are accurately determined. The three-laser study demonstrates a method for probing resonances in the H (Formula presented.) ionisation continuum with wave-function density at large internuclear separation (Formula presented.) 4–5 a.u., large angular momenta J, and energy range 131,100–133,000 cm-1, a hitherto unexplored territory. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
- ItemNonlinear optical mechanism of forming periodical nanostructures in large bandgap dielectrics(Les Ulis : EDP Sciences, 2013) Grunwald, R.; Das, S.K.; Debroy, A.; McGlynn, E.; Messaoudi, H.Nonlinear excitation mechanisms of plasmons and their influence on femtosecond-laser induced sub-wavelength ripple generation on dielectric and semiconducting transparent materials are discussed. The agreement of theoretical and experimental data indicates the relevance of the model.
- ItemGeneration of millijoule few-cycle pulses at 5 μm by indirect spectral shaping of the idler in an optical parametric chirped pulse amplifier(Washington, DC : Soc., 2018) Bock, Martin; Grafenstein, Lorenz von; Griebner, Uwe; Elsaesser, ThomasSpectral pulse shaping in a high-intensity midwave-infrared (MWIR) optical parametric chirped pulse amplifier (OPCPA) operating at 1 kHz repetition rate is reported. We successfully apply a MWIR spatial light modulator (SLM) for the generation of ultrashort idler pulses at 5 μm wavelength. Only bulk optics and active phase control of the 3.5 μm signal pulses via the SLM are employed for generating compressed idler pulses with a duration of 80 fs. The 80-fs pulse duration corresponds to less than five optical cycles at the central wavelength of 5.0 μm. The pulse energy amounts to 1.0 mJ, which translates into a peak power of 10 GW. The generated pulse parameters represent record values for high-intensity MWIR OPCPAs.