Group-velocity-matched cascaded quadratic nonlinearities of femtosecond pulses in periodically poled MgO:LiNbO3

Large nonlinear phase shifts were generated with femtosecond pulses at 1560 nm through cascaded quadratic interactions in periodically poled MgO-doped LiNbO3. The off-diagonal component of the nonlinear coefficient was utilized for simultaneous quasi phase matching and group-velocity matching. The effective nonlinear refractive index was varied from -2.9 x 10(-14) to +3.3 x 10(-14) cm2/W by tuning the phase-mismatch conditions.     

Reactivity of cobaloxime bound to polystyrene chain by carbon–cobalt σ bond

The (alkyl)-bis(dimethylglyoximato)pyridinecobalt attached to polychloromethylstyrene by a cobalt–carbon bond was prepared by the reaction of Co(II)(DH)₂Py with polychloromethylstyrene in benzene. The fraction of p-vinylbenzyl·Co(DH)₂Py introduced to the polymer was 8.1 and 2.1 mole %. The photodecomposition of the polymer-bonded cobaloxime was investigated by following the change of the visible spectrum. The rate constant k_dec of the polymer-bonded cobaloxime was 1.1 × 10^?2 sec^?1 in benzene; it is one-fourth of that of its monomeric analog, benzyl·Co(DH)₂Py. The k_dec values of the cobaloximes were also measured in benzene–dimethyl sulfoxide mixed solvents, and the polymer effects were discussed. The dependence of the photodecomposition on energy of the irradiation light was investigated, and it was found that the absorption band near 470 nm is important for the photodecomposition of the cobalt–carbon bond. Spectroscopic measurements of the ligand exchange reaction of polymer-bonded cobaloxime with pyridine in dimethyl sulfoxide gave a larger equilibrium constant (1.2 × 10⁴ liter/mole) than that of benzyl·Co(DH)₂Py (9.4 × 10² liter/mole). The kinetic data of the ligand exchange reaction indicated that the larger equilibrium constant for the polymeric system is due to the smaller rate constant of the reverse reaction. The thermodynamic parameters were also obtained.     

Effect of the Conformation of Polymer Chain on the Reduction Rate of Polyacrylatopentaamminecobalt(III) by Polymer-Bound Ferrous Chelates and the Excited State of Tris(Bipyridine)Ruthenium(Ii)

Electron transfer reactions of Co(NH₃)₅PAA (PAA = polyacrylic acid) with either the polyanionic polymer-bound ferrous chelate, Fe¹¹P-SS (P-SS = vinylbenzylaminediacetate-co-styrenesulfonate) or the uncharged polymer-bound ferrous chelate, Fe¹¹P-VPRo (P-VPRo = vinylbenzylaminediacetate-co-vinylpyrrolidone), and the Ru(bpy)²⁺ ₃ photosensitized reduction of Co(NH₃)₅PAA have been investigated in aqueous solutions at pH 5.4, I = 0.06 (I is ionic strength), and 25°C. For the ferrous chelate reductions, the second-order rate constants for Fe¹¹-PSS and Fe¹¹P-VPRo were almost equal to that for the corresponding nonpolymer-bound ferrous chelate, Fe¹¹BDA (BDA = benzylaminediacetate). The results indicate that there is no appreciable steric hindrance due to the polymer chains of the polymer-bound ferrous chelates and that the effect of columbic repulsion force between the polyanion chains can be ignored for the reaction of Co(NH₃)₅PAA with Fe¹¹P-SS. The results also suggest that there are two kinds of the pendant Co(III) species, “reactive” and “inert.” The inert Co(III) species are shielded by the polymer chains from attack of the Fe(II) chelates that are present in the bulk solutions. A similar reaction behavior was observed in the Ru(bpy)²⁺ ₃ photosensitized reduction of Co(NH₃)₅PAA at pH 5.4. For the Co(III) complex having an extremely few Co(III) complex moieties on the polymer chain, almost all of the Co(III) groups were hardly reduced by the excited state of Ru(bpy)²⁺ ₃, and reverse quenching occurred due to binding of the Ru(bpy)²⁺ ₃ to the polyacrylic acid chain of the polymer complex. On the other hand, for Co(NH₃)₅PAA with a relatively large number of the Co(III) moieties on the polymer chain, lifetime measurements at a higher concentration of the Ru(bpy)²⁺ ₃ showed a double-exponential fit, which suggests that there are two parallel decay processes. The fast and slow components mainly correspond to the decays: Ru(bpy)²⁺ ₃ quenched by Co(III) and reverse quenching due to binding of Ru(bpy)²⁺ ₃ into the compact polymer chains.     

Joint temporal density measurements for two-photon state characterization

We demonstrate a technique for characterizing two-photon quantum states based on joint temporal correlation measurements using time-resolved single-photon detection by femtosecond up-conversion. We measure for the first time the joint temporal density of a two-photon entangled state, showing clearly the time anticorrelation of the coincident-frequency entangled photon pair generated by ultrafast spontaneous parametric down-conversion under extended phase-matching conditions. The new technique enables us to manipulate the frequency entanglement by varying the down-conversion pump bandwidth to produce a nearly unentangled two-photon state that is expected to yield a heralded single-photon state with a purity of 0.88. The time-domain correlation technique complements existing frequency-domain measurement methods for a more complete characterization of photonic entanglement.     

Room temperature femtosecond optical parametric generation in MgO-doped stoichiometric LiTaO3

We demonstrate room temperature femtosecond optical parametric generation with high average output power in periodically poled MgO-doped stoichiometric LiTaO₃. Direct pumping with 725-fs pulses from a passively mode-locked thin disk laser at 1030 nm resulted in stable 1.5 W average signal power at 1484 nm at the full laser repetition rate of 59 MHz. With this demonstration we achieved a significant simplification of our recently presented red-green-blue laser source because no temperature stabilization of any nonlinear crystal is required. PACS 42.65.Yj; 42.70.Mp; 42.79.Nv     

Synthesis of optically active lipopeptide analogs from the outer membrane of Escherichia coli.

The synthesis of optically active lipopeptide derivatives has been accomplished by the use of chiral glycerol derivatives. Lipopeptide derivatives with (R)-glycerol moieties showed higher mitogenic activities than those with the (S)-configuration. N-2,2,2-Trichloroethoxycarbonyl lipopeptide derivatives increased mitogenic activity.     

Preparation and properties of some water-soluble cobalt (III)–poly-4-vinylpyridine complexes

Water-soluble cobalt(III) chelates having a polymeric ligand such as cis-[Co(en)_2-PVPCl]Cl₂ and cis-[Co-(trien)PVPCl]Cl₂ (PVP = poly-4-vinylpyridine) were prepared by substitution reactions between cobalt(III) chelate and PVP in water–alcohol solution. PVP of different degrees of polymerization was used as the ligand in preparation of these complexes. The PVP complexes were identified and their properties ascertained by microanalysis and by a study of the infrared, ultraviolet, visible, and PMR spectra. Most of the characteristic properties of these complexes may be ascribed to the polymeric structure of the PVP ligand.     

Green-pumped high-power optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3

A high-power 532 nm-pumped multikilohertz nanosecond optical parametric oscillator using a periodically poled 1.0 mol.% MgO-doped stoichiometric lithium tantalate crystal that could be operated from room temperature to 200 degrees C without damage is reported. A broad continuous tuning range from 855 to 1410 nm was achieved within a single domain period. Efficient operation of high peak power and watt level average power with a power conversion of 62.5% was measured. These results show that a high-resolution high average power visible tunable source can be realized.