Relation between the cavity detuning and the output opticalintensity in free-electron lasers

The authors use a simple model of saturation in free-electron lasers operating with pulsed beams to study the intensity growth as a function of the cavity mismatch and of the coupling parameter. In spite of the simplicity of the model, the dependence of the intracavity power, as a function of the cavity detuning, is reproduced remarkably well. It is also pointed out that an enhancement of the optical power is obtained by adjusting the cavity length while the optical signal grows. The problem is analyzed qualitatively and realization schemes are proposed     

Scalable arrays of chemical vapor sensors based on DNA-decorated graphene

Arrays of chemical vapor sensors based on graphene field effect transistors functionalized with single-stranded DNA have been demonstrated. Standard photolithographic processing was adapted for use on large-area graphene by including a metal protection layer, which protected the graphene from contamination and enabled fabrication of high quality field-effect transistors （GFETs）. Processed graphene devices had hole mobilities of 1,640 ± 250 cm2.V-1.s-1 and Dirac voltages of 15 ± 10 V under ambient conditions. Atomic force microscopy was used to verify that the graphene surface remained uncontaminated and therefore suitable for controlled chemical functionalization. Single-stranded DNA was chosen as the functionalization layer due to its affinity to a wide range of target molecules and π-π stacking interaction with graphene, which led to minimal degradation of device characteristics. The resulting sensor arrays showed analyte- and DNA sequence-dependent responses down to parts-per-billion concentrations. DNA/GFET sensors were able to differentiate among chemically similar analytes, including a series of carboxylic acids, and structural isomers of carboxylic acids and pinene. Evidence for the important role of electrostatic chemical gating was provided by the observation of understandable differences in the sensor response to two compounds that differed only by the replacement of a （deprotonating） hydroxyl group by a neutral methyl group. Finally, target analytes were detected without loss of sensitivity in a large background of a chemically similar, volatile compound. These results motivate further development of the DNA/graphene sensor family for use in an electronic olfaction system.     

Gain parameterization formulas in FEL optical-klystronconfigurations

We discuss simple formulas useful to analyze the free-electron laser dynamics when an optical-klystron configuration is employed. The small-signal gain dependence on the length of the dispersive section is discussed, as well as the effects of the inhomogeneous broadening contributions. We introduce the concept of saturation intensity for the optical-klystron and study the dependence on the various parameters of the device. We investigate the high gain effects and the saturated behavior. Regarding this last point, we present a formula accounting for the optical gain dependence on the intracavity power     

Lawson-Penner limit and single passage free electron lasers performances

The limits of the performances of a single passage FEL device imposed by the Lawson-Penner law are discussed within the framework of the super mode theory.     

Free electron lasers operating with variably polarization undulators

We discuss the properties of Free Electron Lasers (FEL) operating with variably polarizing undulators. We study the characteristics of the electron motion in this type of undulators and analyze the spectral properties of the emitted radiation. We also derive general expressions for the small signal gain coefficient and for the saturation intensity. Finally, we explore the characteristics of FEL operation in the hypothesis of Optical-Klystron configuration with particular reference to devices exploiting undulators with opposite polarizations. Regarding this last point, we show that interference may produce undesidered effects which may reduce rather than increase the small signal gain.     

Optimisation of sintered glass–ceramics from an industrial waste glass

Industrial plasma melting of municipal solid waste (MSW) incinerator fly ashes leads to a glass that may be easily crystallised to gehlenite glass–ceramics, by the sintering of fine glass powders. However, since the glass composition is not optimised for glass–ceramic manufacturing, the viscous flow is much hindered by a very significant surface crystallisation and dense glass–ceramics are feasible only by sintering above 1000 °C. This paper reports a new strategy for obtaining dense and strong glass–ceramics at 950 °C, with a holding time of only 30 min, consisting of the mixing of waste glass with a secondary recycled glass, such as soda-lime–silica glass or borosilicate glass. For an optimum balance between the two types of glass also the addition of kaolin clay, in order to favour the shaping, was found to be feasible. The approach had a positive effect, besides on the mechanical properties (e.g. bending strength exceeding 100 MPa), on the chemical stability.