Showing papers by "John B Ketterson published in 2010"
TL;DR: The theoretical studies confirm the experimental results and show that gamma-NaAsSe(2) has the highest static SHG coefficient known to date, 337.9 pm/V, among materials with band gaps larger than 1.0 eV.
Abstract: AAsSe(2) (A = Li, Na) have been identified as a new class of polar direct-band gap semiconductors These I-V-VI(2) ternary alkali-metal chalcoarsenates have infinite single chains of (1/infinity)[AsQ(2)(-)] derived from corner-sharing pyramidal AsQ(3) units with stereochemically active lone pairs of electrons on arsenic The conformations and packing of the chains depend on the structure-directing alkali metals This results in at least four different structural types for the Li(1-x)Na(x)AsSe(2) stoichiometry (alpha-LiAsSe(2), beta-LiAsSe(2), gamma-NaAsSe(2), and delta-NaAsSe(2)) Single-crystal X-ray diffraction studies showed an average cubic NaCl-type structure for alpha-LiAsSe(2), which was further demonstrated to be locally distorted by pair distribution function (PDF) analysis The beta and gamma forms have polar structures built of different (1/infinity)[AsSe(2)(-)] chain conformations, whereas the delta form has nonpolar packing A wide range of direct band gaps are observed, depending on composition: namely, 111 eV for alpha-LiAsSe(2), 160 eV for LiAsS(2), 175 eV for gamma-NaAsSe(2), 223 eV for NaAsS(2) The AAsQ(2) materials are soluble in common solvents such as methanol, which makes them promising candidates for solution processing Band structure calculations performed with the highly precise screened-exchange sX-LDA FLAPW method confirm the direct-gap nature and agree well with experiment The polar gamma-NaAsSe(2) shows very large nonlinear optical (NLO) second harmonic generation (SHG) response in the wavelength range of 600-950 nm The theoretical studies confirm the experimental results and show that gamma-NaAsSe(2) has the highest static SHG coefficient known to date, 3379 pm/V, among materials with band gaps larger than 10 eV
191 citations
TL;DR: It is demonstrated that starting from noncentrosymmetric phase-change materials such as APSe(6) (A = K, Rb), the authors can obtain optical glass fibers with strong, intrinsic, and temporally stable second-order nonlinear optical (NLO) response.
Abstract: We report that the one-dimensional polar selenophosphate compounds APSe6 (A = K, Rb), which show crystal−glass phase-change behavior, exhibit strong second harmonic generation (SHG) response in both crystal and glassy forms. The crystalline materials are type-I phase-matchable with SHG coefficients χ(2) of 151.3 and 149.4 pm V−1 for K+ and Rb+ salts, respectively, which is the highest among phase-matchable nonlinear optical (NLO) materials with band gaps over 1.0 eV. The glass of APSe6 exhibits comparable SHG intensities to the top infrared NLO material AgGaSe2 without any poling treatments. APSe6 exhibit excellent mid-IR transparency. We demonstrate that starting from noncentrosymmetric phase-change materials such as APSe6 (A = K, Rb), we can obtain optical glass fibers with strong, intrinsic, and temporally stable second-order nonlinear optical (NLO) response. The as-prepared glass fibers exhibit SHG and difference frequency generation (DFG) responses over a wide range of wavelengths. Raman spectroscopy...
79 citations
TL;DR: RbAg( 2)TeS(6) and CsAg(2) TeS( 6) are air- and water-stable, wide-band-gap semiconductors exhibiting nonlinear-optical second-harmonic generation.
Abstract: The layered compounds RbAg(2)TeS(6) and CsAg(2)TeS(6) crystallize in the noncentrosymmetric space group P6(3)cm, with a = 19.15 A, c = 14.64 A, and V = 4648 A(3) and a = 19.41 A, c = 14.84 A, and V = 4839 A(3), respectively. The structures are composed of neutral [Ag(2)TeS(3)] layers alternating with charge-balanced salt layers containing polysulfide chains of [S(6)](2-) and alkali-metal ions. RbAg(2)TeS(6) and CsAg(2)TeS(6) are air- and water-stable, wide-band-gap semiconductors (E(g) ∼ 2.0 eV) exhibiting nonlinear-optical second-harmonic generation.
25 citations
TL;DR: This work fabricated line gratings from periodically etched fused silica on which a thin silver film is deposited that is in turn covered with a silica index-matched fluid and an ultrasharp LRSPP linewidth of 4 nm is observed.
Abstract: We have fabricated line gratings from periodically etched fused silica on which a thin silver film is deposited that is in turn covered with a silica index-matched fluid. This dielectrically symmetric geometry supports an independent long-range surface plasmon-polariton (LRSPP) and a short-range surface plasmon polariton, and the associated plasmonic band structure has been probed. Coupling to external light is achieved via the patterned grating, and an ultrasharp LRSPP linewidth of 4 nm is observed. The experimental results are compared with finite-difference time-domain simulations.
18 citations
TL;DR: In this article, the authors estimate the experimental polariton density achievable and propose a direction for polariton-based Bose-Einstein condensation in Cu.O when the input laser frequency is tuned to the two-photon quadrupole polariton resonance.
Abstract: O when the input laser frequency is tunedto the two-photon quadrupole polariton resonance. The Z-scan response at allows us to accurately estimatethe absolute number of polaritons generated via two-photon absorption. A striking dip is observed near the 2Z-scan focus which basically arises fromAuger-type recombination of polaritons. Under high excitation levels,the 3 Z-scan shows strong third harmonic generation. Based on the nonlinear optical parameters determined,we estimate the experimental polariton density achievable and propose a direction for polariton-based Bose-Einstein condensation in Cu
10 citations
TL;DR: Qualitatively, some strategies to probe single particle and collective responses in normal and superfluid 3He in a frequency and wave-vector specific manner with the goal of stimulating such experiments in the future are described.
Abstract: Techniques for studying the combined temporal and spatial response of 3He are few in number. Here we describe, qualitatively, some strategies to probe single particle and collective responses in normal and superfluid 3He in a frequency and wave-vector specific manner with the goal of stimulating such experiments in the future.
2 citations
TL;DR: In this article, the new compounds (III) crystallize in the noncentrosymmetric space group P63cm with Z = 18.5 cm and Z = 0.
Abstract: The new compounds (III) crystallize in the noncentrosymmetric space group P63cm with Z = 18.
1 citations
TL;DR: AAsSe(2) (A = Li, Na) has been identified as a new class of polar direct-band gap semiconductors as mentioned in this paper, which can be used for solution processing.
Abstract: AAsSe(2) (A = Li, Na) have been identified as a new class of polar direct-band gap semiconductors. These I-V-VI(2) ternary alkali-metal chalcoarsenates have infinite single chains of (1/infinity)[AsQ(2)(-)] derived from corner-sharing pyramidal AsQ(3) units with stereochemically active lone pairs of electrons on arsenic. The conformations and packing of the chains depend on the structure-directing alkali metals. This results in at least four different structural types for the Li(1-x)Na(x)AsSe(2) stoichiometry (alpha-LiAsSe(2), beta-LiAsSe(2), gamma-NaAsSe(2), and delta-NaAsSe(2)). Single-crystal X-ray diffraction studies showed an average cubic NaCl-type structure for alpha-LiAsSe(2), which was further demonstrated to be locally distorted by pair distribution function (PDF) analysis. The beta and gamma forms have polar structures built of different (1/infinity)[AsSe(2)(-)] chain conformations, whereas the delta form has nonpolar packing. A wide range of direct band gaps are observed, depending on composition: namely, 1.11 eV for alpha-LiAsSe(2), 1.60 eV for LiAsS(2), 1.75 eV for gamma-NaAsSe(2), 2.23 eV for NaAsS(2). The AAsQ(2) materials are soluble in common solvents such as methanol, which makes them promising candidates for solution processing. Band structure calculations performed with the highly precise screened-exchange sX-LDA FLAPW method confirm the direct-gap nature and agree well with experiment. The polar gamma-NaAsSe(2) shows very large nonlinear optical (NLO) second harmonic generation (SHG) response in the wavelength range of 600-950 nm. The theoretical studies confirm the experimental results and show that gamma-NaAsSe(2) has the highest static SHG coefficient known to date, 337.9 pm/V, among materials with band gaps larger than 1.0 eV.
TL;DR: In this paper, a two-photon four-wave mixing experiment was conducted to probe for Bose-Einstein condensation of excitons in thin films, and a relatively simple set of equations describing the dynamics of the system was obtained for a particular configuration of the three incident beams, and numerical and approximate analytical solutions were found.
Abstract: We propose and theoretically investigate a two-photon four-wave mixing experiment to probe for Bose-Einstein condensation of excitons in ${\text{Cu}}_{2}\text{O}$ thin films. A relatively simple set of equations describing the dynamics of the system is obtained for a particular configuration of the three incident beams, and numerical and approximate analytical solutions are found. When one takes into account the boundary conditions, which result in reflections from the interfaces, the characteristics of the resulting phase-conjugated signal will exhibit Fabry-Perot-type oscillations. For film thicknesses equal to a multiple of a half wavelength in the film the resulting signal is enhanced by more than an order of magnitude relative thicknesses that are an odd multiple of a quarter wavelength. In this case the contribution from accompanying excitonic condensates with wave vectors $\ifmmode\pm\else\textpm\fi{}2\mathbf{k}$ is minimal. Therefore, the resulting phase-conjugated signal vs the delay time between the pump and probe pulses yields a direct measure of the time evolution only of the exciton condensate with wave vector $\mathbf{k}=\mathbf{0}$.