Laser à colorant | EPFL Graph Search

vignette|316x316px|Gros plan d'un laser à colorant CW de table à base de rhodamine 6G, émettant à 580 nm (jaune). Le faisceau laser émis est visible sous forme de lignes jaunes pâles entre la fenêtre jaune (au centre) et l'optique jaune (en haut à droite), où il se reflète à travers l'image vers un miroir invisible, et revient dans le jet de colorant depuis le coin inférieur gauche. La solution de colorant orange entre dans le laser par la gauche et sort par la droite, toujours brillante de phosphorescence triplet, et est pompée par un faisceau de 514 nm (bleu-vert) provenant d'un laser à argon. Le laser de la pompe peut être vu entrant dans le jet de colorant, sous la fenêtre jaune. Un laser à colorant est un laser qui utilise un colorant organique comme milieu laser, généralement sous forme de solution liquide. Par rapport aux gaz et à la plupart des supports laser à semi-conducteurs, un colorant peut généralement être utilisé pour une gamme de longueurs d'onde beaucoup plus large ,

Functional Elements for Quantum-Dot-Based Integrated Quantum Photonics

Antoine Maxime Delgoffe

Quantum Integrated Photonics (QIP) harnesses quantum-states of light on tiny chips, from generation to processing and eventual detection. Within this context, this thesis explores functional QIP elements resulting from the monolithic integration of semiconductor quantum dots (QDs) in tailored photonic crystal systems of coupled cavities and waveguides. QDs present atom-like optical and electronic properties, which make them ideal for a deterministic, on-demand generation of single photons. Such QD-based devices can be expected to provide solutions for applications of QIP in quantum computing, communication and metrology. Here, we exploit the pyramidal site-controlled QD technology to reproducibly fabricate quantum photonic elements in which an arbitrary number of QD quantum emitters are embedded in photonic crystal (PhC) structures with alignment precision better than 50nm. Systematic investigation of reference structures with dense arrays of QDs to observe optical mode structures, and identical structures with only a few QDs for selective excitation and coupling to prescribed modes, is conducted using spatially-resolved micro-photoluminescence spectroscopy. Observations are consolidated by quantitative comparisons to 2D FDM numerical simulations. First, defect-potential PhC cavities are made by precise transverse shifts of selected holes in a PhC defect waveguide. In these structures, defect modes confined by a local mismatch in the photonic dispersion are observed, with peculiar polarization signatures. The fundamental defect modes display quality factors and mode volumes on par with conventional Ln=3 cavities. Defect modes can be selectively excited, and weak coupling of a single QD to cavity modes is demonstrated using thermal tuning. Next, tilted-potential PhC cavities supporting Airy-Bloch photonic modes are realized by staggered shifts of holes from 0 to smax along the axis. Such modes are suitable for local interaction and extraction of single photons from site-controlled QDs and their transmission to remote locations. Selective excitation of several modes with properly positioned QDs is demonstrated. Weak coupling of a QD to a single mode is achieved by thermal tuning, showing features of Purcell effect. The quasi linear energy-position dispersion of the Airy-Bloch modes maxima provides a mean for constructing an efficient wavelength-multiplexed single-photon injector. Finally, a monolithic model structure, consisting of two PhC waveguides side-coupled to a center Ln=3 cavity, with four ports connected to suspended nanobeams and grating couplers for light extraction/injection, is fabricated and tested. Five QDs are embedded in specific positions; four can act as on-chip single photon sources while the fifth, embedded in the center cavity, could be used for photon processing functions. The quasi-resonant excitation of this fifth QD via its p-shell is demonstrated using a pump laser beam that is injected into a waveguide through the grating coupler. Part of the s-shell emission is coupled to another targeted optical channel, demonstrating a complete photonic connectivity of all elements, a fundamental requirement towards on-chip processing. The results of this thesis consolidate the assets of the site-controlled pyramidal QD technology and tailored PhC confinement towards the realization of functional elements for quantum integrated photonics circuits.

EPFL2020

Doping-induced charge trapping in organic light-emitting devices

Detlef Berner, Frank Nüesch, Eduard Tutis, Xiao Wang, Libero Zuppiroli

By using pyran-containing donor-acceptor dyes as doping molecules in organic light-emitting devices (OLEDs), we scrutinize the effects of charge trapping and polarization induced by the guest molecules in the electro-active host material. Laser dyes 4-(dicyanomethylene)-2-methyl-6-[2-[(julolidin-9-yl)phenyl]ethenyl]-4H-pyran (DCM2) and the novel 4-(dicyanomethylene)-2-methyl-6-[2-[(4-diphenylamino)phenyl]ethenyl]-4H-pyran (DCM-TPA) are used as model compounds. The emission color of these polar dyes depends strongly on doping concentration, which we have attributed to polarization effects induced by the doping molecules themselves. Their frontier orbital energy levels are situated within the bandgap of the tris(8-hydroxyquinoline)aluminum (Alq3) host matrix and allow the investigation of either electron trapping or both electron and hole trapping. In the case of DCM-TPA doping, we were able to show that electron trapping leads to a partial shift of the recombination zone out of the doped Alq3 region. To impede charge-recombination processes taking place in the undoped host matrix, a charge-blocking layer efficiently confines the recombination zone inside the doped zone and gives rise to increased luminous efficiency. For a doping concentration of 1 wt.-% we obtain a maximum luminous efficiency of 10.4 cd A-1. At this doping concentration, the yellow emission spectrum shows excellent color saturation with CIE chromaticity coordinates x, y of 0.49 and 0.50, respectively. In the case of DCM2 the recombination zone is much less affected for the same doping concentrations, which is ascribed to the fact that both electrons and holes are being trapped. The experimental findings are corroborated with a numerical simulation of the doped multilayer devices

Wiley-VCH2005

Functional Elements for Quantum-Dot-Based Integrated Quantum Photonics

Antoine Maxime Delgoffe

EPFL2020