Femtosecond laser crystallization of amorphous Ge

Cataloged from PDF version of article.Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm(-1) as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601356

Crystallization of Ge in SiO2 matrix by femtosecond laser processing

Cataloged from PDF version of article.Germanium nanocrystals embedded in a siliconoxide matrix has been fabricated by single femtosecond laser pulse irradiation of germanium doped SiO2 thin films deposited with plasma enhanced chemical vapor deposition. SEM and AFM are used to analyze surface modification induced by laser irradiation. Crystallization of Ge in the oxide matrix is monitored with the optic phonon at 300 cm(-1) as a function of laser fluence. Both the position the linewidth of the phonon provides clear signature for crystallization of Ge. In PL experiments, strong luminescence around 600 nm has been observed. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3677829

Electrochemically tunable ultrafast optical response of graphene oxide

Cataloged from PDF version of article.We demonstrate reversible and irreversible changes in the ultrafast optical response of multilayer graphene oxide thin films upon electrical and optical stimulus. The reversible effects are due to electrochemical modification of graphene oxide, which allows tuning of the optical response by externally applied bias. Increasing the degree of reduction in graphene oxide causes excited state absorption to gradually switch to saturable absorption for shorter probe wavelengths. Spectral and temporal properties as well as the sign of the ultrafast response can be tuned either by changing the applied bias or exposing to high intensity femtosecond pulses. © 2011 American Institute of Physics

Attractive versus repulsive excitonic interactions of colloidal quantum dots control blue- to red-shifting (and non-shifting) amplified spontaneous emission

Tunable, high-performance, two-photon absorption (TPA)-based amplified spontaneous emission (ASE) from near-unity quantum efficiency colloidal quantum dots (CQDs) is reported. Besides the absolute spectral tuning of ASE, the relative spectral tuning of ASE peak with respect to spontaneous emission was shown through engineering excitonic interactions in quasi-type-II CdSe/CdS core/shell CQDs. With core-shell size adjustments, it was revealed that Coulombic exciton-exciton interactions can be tuned to be attractive (type-I-like) or repulsive (type-II-like) leading to red- or blue-shifted ASE peak, respectively, and that nonshifting ASE can be achieved with the right core-shell combinations. The possibility of obtaining ASE at a specific wavelength from both type-I-like and type-II-like CQDs was also demonstrated. The experimental observations were supported by parametric quantum-mechanical modeling, shedding light on the type-tunability. These excitonically engineered CQD-solids exhibited TPA-based ASE threshold as low as 6.5 mJ/cm2 under 800 nm excitation, displaying one of the highest values of TPA cross-section of 44 660 GM. © 2013 American Chemical Society

Nonlinear absorption behaviors of filled and unfilled d shell metal complexes of 5, 10, 15, 20-tetrakis(4-hydroxyphenyl)porphyrin

We study nonlinear absorption behaviors of 5, 10, 15, 20-tetrakis(4-hydroxyphenyl)porphyrins with the central metal ions: Zn(2+), Ni(2+), Co(2+), and Fe(3+) by open aperture Z-scan technique with 65 ps or 4 ns pulse duration. For 65 ps pulse duration the filled d shell compounds exhibit nonlinear absorption while the unfilled d shell compounds exhibit saturable absorption. For 4 ns pulse duration Ni, Co and Fe compounds exhibit nonlinear absorption at high fluence while Ni compound exhibits saturable absorption at low fluence. The observed nonlinear absorption behaviors depending on the central metal ion and pulse duration are discussed using excited-state lifetimes found from pump-probe spectroscopy. (C) 2011 Elsevier B. V. All rights reserved

Blue-and red-shifting amplified spontaneous emission of CdSe/CdS core/shell colloidal quantum dots

We report blue-and red-shifting amplified spontaneous emission of CdSe/CdS quantum dots, controlled by varying core/shell dimensions and modifying exciton-exciton interactions, with low optical gain threshold of two-photon absorption pumping. © OSA 2013

Soil Moisture Product Validation Good Practices Protocol Version 1.0

The role of soil moisture in the water, energy and carbon cycle of the Earth cannot be understated. Soil moisture has a major impact on agriculture, land surface hydrology, weather and climate forecasting. Soil moisture is responsible for the partitioning of solar energy into latent and sensible heat flux at the Earth's surface, which is a key element of the energy cycle. Soil moisture also partitions precipitation into soil water, ground water, and surface runoff. Thus, land surface hydrology is critically concerned with monitoring and modeling surface soil moistureas it influences infiltration and therefore land surface runoff (Figure 1). Soil moisture is a primary concern for agriculture where it is a necessary element for growth and also the mechanism for movement of nutrients towards crops, impacting yield and productivity. Weather and climate forecasting can see great advances in skill with the incorporation of soil moisture state into models