Ionization energies of cesium and cesium oxide clusters

The vertical ionization potentials of 7 cesium and 86 oxidized cesium clusters were determined using the technique of photoionization mass spectrometry. The spectra were obtained using a tunablecw dye laser for clusters in a mass range 1 to 2024 amu. The vertical ionization potentials (IP) are presented as a function of size and composition. The ionization energies of cesium clusters, Cs_n, decrease with cluster size. Unusually low IP were observed for the enneamer, Cs₉, and for the cesium monoxide Cs₁₁ O. With increasing oxidation of the cesium metal clusters the IP decreases (suboxides) reaches a minimum at Cs(Cs₂O)_n and then increases (superoxides).     

Determination of mazindol in human oral fluid by high performance liquid chromatography–electrospray ionization mass spectrometry

Brazil is one of the countries most affected by abuse of stimulant medications by professional drivers, especially fenproporex, amfepramone and mazindol. Even though their sale is banned, they can be found in illegal markets, such as those located on the country's borders. The use of oral fluid to monitor drug levels has many advantages over plasma and urine because it is noninvasive, easier to collect and more difficult to adulterate. The aim of this study was to develop and validate a sensitive and specific method to quantify mazindol in human oral fluid by liquid chromatography–mass spectrometry (LC‐MS). The LC system consisted of an LC‐MS system operated in selected ion monitoring mode. The mobile phase was composed of water at pH 4.0, acetonitrile and methanol (60:15:25 v/v/v) at a flow rate of 1.0 mL/min and propranolol was used as internal standard. Total running time was 10 min. The lower limit of quantification was 0.2 ng/mL and the method exhibited good linearity within the 0.2–20 ng/mL range (r = 0.9987). A rapid, specific, sensitive, linear, precise and accurate method was developed for determination of mazindol in human oral fluid according to European Medicines Agency guidelines, and is suitable for monitoring mazindol levels in oral fluid of professional drivers. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of drawing tension on the photosensitivity of Sn-Ge- and B-Ge-codoped core fibers

The influence of drawing tension on the formation of Bragg gratings in B-Ge- and Sn-Ge-codoped core fibers is investigated by transmission and stress measurements. With increasing drawing tension, the axial stress is reduced in the B-Ge-codoped core but increased in the Sn-Ge-codoped core. A higher drawing tension leads to a photosensitivity enhancement and an increase of the core stress during the grating formation in B-Ge-codoped fibers. For Sn-Ge-codoped fibers, increased drawing tension results in an UV-induced stress decrease accompanied by a reduction of the photosensitivity. The results are discussed on the basis of an UV-induced compaction of the core network.     

Fabrication of high-mechanical-resistance Bragg gratings in single-mode optical fibers with continuous-wave ultraviolet laser side exposure

The mechanical resistance of single-mode fibers containing fiber Bragg gratings inscribed with cw UV laser irradiation is almost identical to that of pristine fiber. The median breaking strength of the gratings' Weibull distribution is more than 5 GPa, and the m value is of the order of 70. Based on a dynamic fatigue model, a Bragg grating lifetime of 50 years with a failure probability of 0.001 is predicted, assuming a constant applied stress of 0.96 GPa.     

Birefringence writing and erasing in ultra-low-birefringence fibers by polarized ultraviolet side-exposure: origin and applications

This paper presents a new method for writing and erasing a birefringence in optical fibers by polarized ultra violet side-exposure. This experiment gives new insight into the origin of the induced birefringence and some applications are outlined.     

Phenoxy-benzothiadiazole dyes: Synthesis,photophysical properties and preliminary application in OLEDs

The synthesis of a phenoxy-benzothiadiazole (BTD) derivative is reported for the first time. This derivative was employed as an intermediate in the obtention of two novel highly fluorescent aryl-phenoxy-BTD dyes. Their photophysical properties were evaluated in solution and the results indicate a strong intramolecular charge transfer (ICT) character in the excited state. The luminophore 3a, possessing a donor-BTD-phenoxide architecture, exhibits superior fluorescence quantum yield (0.67) than the designed acceptor-BTD-phenoxide dye (0.06). After electrochemical and photoluminescence characterization of thin films of 3a, an OLED with the configuration ITO/PEDOT:PSS/3a/TPBi/LiF/Al was constructed. This device displayed a green emission centered at 547?nm, with CIE coordinates of (0.40, 0.55). For comparison, an OLED using a previously reported luminescent BTD-pyridyl derivative was also constructed. The OLED made with the phenoxy-BTD derivative operated using less current density and led to higher irradiance and electrical stability, indicating the high potential of ArO-BTD dyes for future application in electroluminescent devices.     

Efficient broadband intracore grating LP(01)-LP(02) mode converters for chromatic-dispersion compensation

LP(01)-LP(02) mode converters based on UV-written intracore gratings have been fabricated for chromatic-dispersion compensation. The mode converters operate in transmission at wavelengths near 150 nm with spectral bandwidths of 14-25 nm and coupling efficiencies of as much as 90%. A large negative dispersion of -335 ps/(nm km) is obtained for a compensator consisting of the mode converter and a 1490-m-long few-mode fiber. The compensator shows negative dispersion over a wavelength region of 5 nm. Its figure of merit is estimated to be 370 ps/(nm dB).     

Embedded optical fiber Bragg grating sensor in a nonuniform strain field: Measurements and simulations

This paper investigates the use of embedded optical fiber Bragg gratings to measure strain near a stress concentration within a solid structure. Due to the nature of a stress concentration (i.e., the strong nonuniformity of the strain field), the assumption that the grating spectrum in reflection remains a single peak with a constant bandwidth is not valid. Compact tension specimens including a controlled notch shape are fabricated, and optical fiber Bragg gratings with different gage lengths are embedded near the notch tip. The form of the spectra in transmission varies between gages that are at different distances from the notch tip under given loading conditions. This variation is shown to be due to the difference in the distribution of strain along the gage length. By using the strain field measured using electronic speckle pattern interferometry on the specimen surface and a discretized model of the grating, the spectra in transmission are then calculated analytically. For a known strain distribution, it is then shown that one can determine the magnitude of the applied force on the specimen. Thus, by considering the nonuniformity of the strain field, the optical fiber Bragg gage functions well as an embedded strain gage near the stress concentration.     

Actively mode-locked visible upconversion fiber laser

Active mode locking of a Pr(3+)/Yb (3+) -doped upconversion fluoride fiber laser with an all-fiber ZnO acousto-optic phase modulator is demonstrated for the first time to the authors' knowledge. Optical pulses of ~550-ps duration with a repetition rate of 239 MHz at a wavelength of 635 nm have been generated.