High-Speed Modulation of a Terahertz Quantum Cascade Laser by Coherent Acoustic Phonon Pulses

The fast modulation of lasers is a fundamental requirement for applications in optical communications, high-resolution spectroscopy and metrology. In the terahertz-frequency range, the quantum-cascade laser (QCL) is a high-power source with the potential for high-frequency modulation. However, conventional electronic modulation is limited fundamentally by parasitic device impedance, and so alternative physical processes must be exploited to modulate the QCL gain on ultrafast timescales. Here, we demonstrate an alternative mechanism to modulate the emission from a QCL device, whereby optically-generated acoustic phonon pulses are used to perturb the QCL bandstructure, enabling fast amplitude modulation that can be controlled using the QCL drive current or strain pulse amplitude, to a maximum modulation depth of 6% in our experiment. We show that this modulation can be explained using perturbation theory analysis. While the modulation rise-time was limited to ~800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible

High-speed modulation of a terahertz-frequency quantum-cascade laser using coherent acoustic phonon pulses

We demonstrate a new method for high-speed modulation of the electron transport and photon generation within a terahertz-frequency quantum-cascade laser (THz QCL). An amplified femtosecond laser is used to generate coherent acoustic-phonon pulses, which are injected into the device, resulting in an electronic bandstructure perturbation, with ~1-ns rise-time. The corresponding change in optical gain allows up to ~6% amplitude modulation, with results explained accurately using a perturbation-theory model

Synthesis and spectroscopic properties of a novel perylenediimide derivative

A novel symmetric 3,4,9,10-perylenetetracarboxylic acid derivative (PDI1) dye based on thiophene donor group was synthesized and characterized by FT-IR and 1H NMR. Cyclic Voltammetry analysis is performed to determine the energy levels of the perylene derivative. Optical characteristics were determined by visible absorption and fluorescence emission spectra. Spectral behavior and fluorescence quantum yield of PDI1 have been measured in different solvents. The dye exhibits high fluorescence quantum yield ( Φf: 0.94-0.99). But the quantum yield PDI1 is very low in the n-butanol solution ( Φf: 0.12). The photophysical properties have important implications for use in a variety of electroactive and photovoltaic applications. A photovoltaic device was fabricated with PDI1 as transporting material. The conversion efficiency for DSSC sensitized by PDI1 is 0.0065%. PDI1 exhibits electrochromic behavior by switching between neutral (red) and oxidized (blue) states. Electron transfer capacity of PDI to the TiO2 was investigated by incorporation of dye as sensitizer in dye sensitized solar cell (DSSC). Soluble dye molecules are very important to prepare dye sensitized solar cell. Solubility was increased with thiophene group

Modulation of the THz Emission by a Quantum Cascade Laser using Coherent Acoustic Phonon Pulses

We use laser-generated coherent acoustic phonon (strain) pulses to modulate the electronic transport and THz emission of a 2.6 THz Ga(Al)As quantum cascade laser. The modulation amplitude is of the order of a few % and the rise time, limited by the measurement system response, is less than 1 nanosecond

High-Speed Modulation of a Terahertz Quantum Cascade Laser Using Coherent Acoustic Phonon Pulses

We demonstrate a new method for high-speed modulation of terahertz emission and electronic transport of a Ga(Al)As quantum cascade laser using coherent acoustic phonon pulses. The modulation, which is on the order of 6%, can be partially explained by a perturbation-theory analysis. The 100 GHz are possible

Photophysical and photochemical properties of a water-soluble perylene diimide derivative

WOS: 000089411700003The absorbance maximum of synthesized water soluble perylene 4-carboxylphenyl-bis-diimide (PECA) is found to be about 50 nm lower in water, as compared to absorbance in organic solvents, and the singlet energy is 61.4 kcal mol(-1) in aqueous solutions, compared to 54.4 kcal mol(-1) in organic solvents. The fluorescence quantum yields were similar in both media but radiative and fluorescence lifetimes are found to be enhanced about twice (tau(f) from 8 to 15 ns), and the rate of fluorescence is decreased twofold in aqueous solution, as compared to organic solutions. PECA is proven to produce reactive superoxide anion and/or hydroperoxy radical in aqueous solutions, in the pH range of 6-12 (phi(O2 .-)(PECA) = 0.062 at pH=9). The superoxide/hydroperoxy formation is found to be enhanced in the presence of ferric ions (phi(O2 .-)(PECA) = 0.10 at pH=9). The quantum yield of flouresence emmission, Q(f), was measured to be 1.00 at pH 11.85, and 0.87 at pH 6.60. The difference is attributed to an aggregation effect due to low solubility in neutral aqueous solution. Fluorescence quenching by Co+2 ions has yielded a quenching rate of 2.3 x 10(12) M-1 s(-1) for perylene diimide. The degradation of bromacil and 2,4-dichlorophenoxyacetic acid (2,4-D) pesticides in neutral aqueous solutions has proven that PECA/Fe+3 solar photocatalyst is as reactive as singlet oxygen in photo oxidations for organic pollutants. High thermal and photo stabilities and the regain of catalysts on precipitation, are the advantages with respect to classical triplet organic photosensitizers (methylene blue, rose bengal, etc.) employed for singlet oxygen photodegradations. (C) 2000 Elsevier Science S.A. All rights reserved

Optical and electrochemical properties of polyether derivatives of perylenediimides adsorbed on nanocrystalline metal oxide films

We report optical and electrochemical properties of polyether derivatives of perylenediimides (PDIs) thin films formed in various materials (semiconductor, insulator, amorphous and self-assembly). Perylenediimides adsorbed on nanocrystalline TiO2 (NT) nanocrystalline alumina (NA), amorphous silicon (PS) and neat self-assemblied (SA) films were prepared and characterized based on spectroscopic, electrochemical, spectro-electrochemical techniques. The absorption and fluorescence spectra of PDIs in chloroform exhibit vibronic features. The fluorescence quantum yields (?f) of PDIs with end amino substituents in chloroform solutions are over 0.95, while the quantum yield of triethoxyphenyl substituted PDI ?f value is 0.024 in solution. Optical spectroscopy proves that PDIs in metal oxide thin films form aggregated type complexes. An electrochromism, a color change from red to blue/violet, is observed on metal oxide films, that indicates existence of mono and dianion forms of PDIs. Reversibility of electrochemical reductions in NT film depends on the scanning rate. However, electrochromism in NA films is stable and reversibility is independent from scanning rate. Stable mono and diaionic species are formed on NA films. SA films show broad absorption peaks during the voltammetric scan. On the other hand, the first reduction onset potentials of PDIs are almost equal to the onset potential of capacitive current of TiO2 which lead to low efficiency in dye-sensitized solar cells. © 2008 Elsevier B.V. All rights reserved.European Commission: FP6 MOLYCELL project-SES-CT-2003-502783 NATO A-2We acknowledge partial funding by the European Commission (FP6 MOLYCELL project-SES-CT-2003-502783), Scientific and Technical Research Council of Turkey (TUBITAK, NATO A-2 support funds) and Alexander von Humbolt Foundation of Germany. We appreciate the project support funds of the State Planning Organization of Turkey (DPT). -

Spectrophotochemical and electrochemical characterization of perylene derivatives adsorbed on nanoporous metaloxide films

ECHOS 2006 Conference -- JUN 28-30, 2006 -- Paris, FRANCEWOS: 000244839000009Electrochemistry of perylene imide and anhydride derivatives adsorbed on semiconductor TiO2 (NT) and insulator Al2O3 (NA) metal oxide films were presented. Adsorption rates on metal oxide surface are observed to be strongly depending on molecular structure. Monoanhydride-monoimide derivatives show two reversible reductions in solution and one reversible reduction in films. Color change from red to blue and violet is observed indicating the formation of monoanion and dianion radicals. Spectroelectrochemical measurements support this interpretation. The color reversal is quite stable in NA films in comparison with NT films