Hans-Jurgen Lydtin

Emission properties of top-layer scandate cathodes prepared by LAD

Abstract In the first part an overview of scandate cathode types, their historical development and the current status of research is given. Then recent improvements obtained by our group are elucidated: A new type of top-layer scandate cathode has been prepared with the aid of laser ablation deposition. Emission current characteristics have been measured as a function of voltage and temperature. Zero field emission i10% is determined as 10% deviation from space-charge law. At 965°CMo-Br i10% of about 400 A/cm2 and at 760°CMo-Br of 32 A/cm2 were achieved, which is more than a factor of 3 higher than the best values for other scandate type cathodes given in literature. It corresponds to a work-function of about 1.16 eV with a Richardson constant of 7.8 A cm−2 K−2. Other emission properties such as uniformity and cathode life are discussed. A description of I U characteristics via the superposition model is given.

Low‐loss optical fibers prepared by plasma‐activated chemical vapor deposition (CVD)

A modified method for the preparation of low‐loss optical fibers by means of chemical vapor deposition (CVD) techniques has been developed. In this method, a nonisothermal plasma is used to stimulate the reactions. Deposition of oxides then occurs only heterogeneously on the substrate. Results obtained by this method show optical losses well below 10 dB/km—having a minimum of 1.4 dB/km at a wavelength of 1050 nm—and a pulse dispersion of 0.8 ns/km.

Hybrid technology for large SM fiber performs

A hybrid technology for the preparation of standard and dispersion-modified single-mode (SM) fibers is discussed. Only the most important central region of the fibers is prepared by plasma chemical vapor deposition (PCVD) techniques. The optical cladding is as a high-purity jacket tube using the normal rod-in-tube obtained from low-cost shaping and sintering technologies. Due to in situ plasma etching, no disturbance is caused by the interfaces. Low attenuation is achieved with less than 5% of the fiber volume consisting of PCVD core region. The hybrid technology allows economic mass production of preforms containing more than 300 km of fiber. >