Adaptive femtosecond pulse shaping to control supercontinuum generation in a microstructure fiber

Efficient confinement of laser radiation in the core of a photonic crystal fiber increases the nonlinear processes resulting in supercontinuum generation. The technique of adaptive pulse shaping using an evolutionary algorithm provides a method to gain control over such highly nonlinear processes. Adaptive pulse shaping of the driving laser radiation passing through the photonic crystal fiber is employed to modify the shape and composition of the output supercontinuum. Amplitude and phase shaping are used to optimize the broadband emission between 500 and 700 nm, as well as a soliton centered at 935 nm. The intensities of the emission and of the soliton driven by a shaped laser pulse increase in comparison to an unshaped pulse by factors of 4 and 3, respectively. The spectral width in the range of 500-600 nm is increased by approximately 40%. In addition, the suppression of self-steepening effects in supercontinuum spectra is demonstrated.     

Thiolated cyclodextrin self-assembled monolayer-like characterized with secondary ion mass spectrometry

In the work the focus is on the preparation of self-assembled monolayer-like films consisting of thiolated cyclodextrin on gold substrate and a characterization by using secondary ion mass spectrometry. The short (1 min) and long (1 h) time preparations of self-assembled monolayer-like films, resulting in submonolayer and monolayer regimes, are investigated, respectively. The observed species of thiolated cyclodextrin (M as molecular ion) self-assembled monolayer-like films are assigned to three groups: Au_xH_yS_z clusters, fragments with origin in cyclodextrin molecule associated with Au, and molecular ions. The group of Au_xH_yS_z (x = 2-17, y = 0-2, z = 1-5) clusters have higher intensities than other species in the positive and even more in negative mass spectra. Interestingly, the dependence between the number of Au and S atoms shows that with the increasing size of Au_xH_yS_z clusters up to 11 Au atoms, the number of associated S atoms is also increasing and then decreasing. Molecular species as (M−S+H)Na⁺, (M+H)Na⁺, AuMNa⁺, (M₂−S)Na⁺, and M₂Na⁺ are determined, and also in cationized forms with K⁺. The intensities of thiolated cyclodextrin fragments at the long time preparation are approximately 10 times higher than the intensities of the same fragments observed at the short time. The largest observed ions in thiolated cyclodextrin self-assembled monolayer-like films are AuM₂ and Au₂M. The thiolated cyclodextrin molecular ions are compared with hexadecanethiol molecular ions in the form of Au_xM_w where the values of x and w are smaller for thiolated cyclodextrin than for hexadecanethiol. This result is supported with larger, more compact, and more stabile thiolated cyclodextrin molecule.     

Preparation of Cyclodextrin–Iron Species in Water by Laser Ablation: Secondary Ion Mass Spectrometry

Supramolecular complexes between cyclodextrin and iron species are studied by using secondary ion mass spectrometry. The iron species are prepared by pulsed‐laser ablation of bulk iron in water; this gives Fe⁺ (56 m/z) and Fe_xO_y⁺ (x, y=1–7) species. Cyclodextrin is added to the water either before or after the laser ablation. When it is added before laser ablation, molecular fragments of cyclodextrin are detected as dehydrated glucopyranose units (C₆H₈O₄⁺) associated with Fe⁺, FeO⁺, and Fe₂O⁺ species. The focus is to observe supramolecular host–guest complexes or adducts between intact molecules of cyclodextrin and iron species. When cyclodextrin is added after laser ablation, the relevant peak at 1210 m/z is observed and assigned as C₄₂H₆₇O₃₅FeNa⁺, which corresponds to a cyclodextrin molecule minus three H atoms. Two possible explanations of this finding are the presence of the host–guest C₄₂H₆₇O₃₅Na–Fe complex, in which Fe is in the cavity, or the presence of the adduct C₄₂H₆₇O₃₄Na–FeO with FeO on the outer surface; the formation of these complexes are supported by the hydrophobicity of Fe and hydrophilicity of FeO, respectively. Due to the presence of 12 % of intact C₄₂H₇₀O₃₅Na–Fe complex and an estimated Fe/FeO ratio of approximately 10², host–guest formation is assumed to be more significant.     

含双脲基团大环化合物的合成及其对卤素阴离子检测研究

通过片段偶联法方便地合成了骨架上含有两个脲基团的O-杂大环化合物骨架cycle 1,并对cycle 1进一步修饰得到了化合物cycle 2和cycle 3.紫外吸收光谱滴定实验表明,二氯甲烷中cycle 2和cycle 3可与卤素阴离子1∶1结合,结合常数为105～108L mol-1,核磁滴定实验证实环上脲基团是阴离子与大环结合的主要位点.     

Fluorescence Dynamics of Coumarin C522 as a Function of Micelle Confinement along with Cyclodextrin Supramolecular Complex Formation

Our aim is to doubly confine a molecule of coumarin C522 in a host–guest supramolecular complex with β‐cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n‐heptane and polar water solvents. Varying the volumes of coumarin C522 and β‐cyclodextrin dissolved in water allows us to control the water‐pool diameters of the reverse micelle in n‐heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n‐heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady‐state and time‐resolved dependences are compared for the two systems coumarin C522(water)/AOT(n‐heptane), denoted C522/micelle, and coumarin C522/β‐cyclodextrin(water)/AOT(n‐heptane), referred to as C522/CD/micelle. The formation of the supramolecular host–guest complex CD–C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n‐heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n‐heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3–5, and w=10–40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3–5 and 10–40 in the steady‐state and time‐resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60–80) and for bound water (25–60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.     

Linear and nonlinear properties of multicomponent glass photonic crystal fibers

Processes resulting in supercontinuum generation in multicomponent glass photonic crystal fibers are reviewed in this paper. Multicomponent glass photonic crystal fibers are shown to have a broad transmission range, extending up to 4.5 μm in selected cases. Pumping with a 1240-nm femtosecond pulse at very low sub-nJ energies resulted in soliton formation and dispersive wave generation in a multicomponent PCF sample having a double-core square-lattice structure. These processes were described using a phase-matching model derived from the simulated dispersive properties of the fiber. Third-harmonic generation was observed in the radiation modes of a different cobweb sample with the simultaneous formation of a soliton in the NIR.     

Nonlinear refractive index of multicomponent glasses designed for fabrication of photonic crystal fibers

The second order nonlinear refractive index n ₂ of various multicomponent glasses was measured at the wavelength of 1240 nm close to the 1.3-μm fiber transmission window. With the refractive index covering the range from 1.45 to 2.3, a comparatively broad range of n ₂ with values from 1.1×10^?20 m²/W for boro-silicate based glass NC21 to 4.3×10^?19 m²/W for lead–bismuth-gallate based glass PBG08 was measured using the Z-scan method. Considering the broad infrared transmission range of multicomponent glasses, these materials pose a great potential for future applications as photonic crystal fiber sources of infrared supercontinuum.     

TOF-SIMS surface analysis of L-Tryptophan self assembled monolayer

This paper dealt with the preparation and characterization of self — assembled monolayersSAM-s of 1-hexadecanethiole and mercapto acetic acid on the silver nanostructure and subsequently the immobilization with amino acid L-Tryptophane. In order to achieve it, we used the electrodeposition of silver onto nanostructured surface of paraffin impregnated graphite electrode (PIGE). Subsequently, we assembled SAM by choosing the 1-hexadecanethiole and mercaptoacetic acid. These two kinds of SAM underwent the functionalization by L-Tryptophan. The observations of silver on PIGE surfaces were performed by scanning electron microscope (SEM). For surface analysis of the SAM functionalized by L-tryphophan, the TOF-SIMS technique was chosen. Finally, the fragmented ions of the immobilized-L-Tryptophan SAM were determined on the basis of suggested residues and three-dimensional structure. The residues show that the ability of L-Tryptophan to build homogeneous structure is better by mercaptoacetic acid SAM structure than by 1-hexadecanethiol. It was observed that L-Tryptophan built compact surface, which, due its chemical properties, can represent very interesting side regarding biocompatibility, homochirality and robustness in the area of life science.