High-quality single phase Nd1+xBa2−xCu3O7−d thin films have been fabricated on SrTiO3 substrates by the laser ablation method. The resistivity of the deposited films are usually lower than that of the YBCO film. The Tc(onset) and Tc(R=0) in the optimized thin films are as high as 91 and 88 K, respectively. The crystallinity of our films are higher than the best YBCO films ever reported. The rocking curve FWHM of the (005) peaks in our thin films is typically 0.05°, which is superior to the best reported YBCO films.

We propose and demonstrate the operation of Q-switched mode-locked square-wave pulses in a thulium-holmium co-doped fiber laser. By using a nonlinear amplifying loop mirror, continuous square-wave dissipative soliton resonance pulse is obtained with 4.4 MHz repetition rate. With the increasing pump power, square-wave pulse duration can be broadened from 1.7 ns to 3.2 ns. On such basis Q-switched mode-locked operation is achieved by properly setting the pump power and the polarization controllers. The internal mode-locked pulses in Q-switched envelope still keep square-wave type. The Q-switched repetition rate can be varied from 41.6 kHz to 74 kHz by increasing pump power. The corresponding average single-pulse energy increases from 2.67 nJ to 5.2 nJ. The average peak power is also improved from 0.6 W to 1.1 W when continuous square-wave operation is changed into Q-switched mode-locked operation. It indicates that Q-switched mode-locked operation is an effective method to increase the square-wave pulse energy and peak power.

The rate of growth of F centres and thermoluminescence studies in highly pure additively coloured and then X-irradiated KC1 crystals show that the first stage of coloration is considerably suppressed and the second stage is enhanced in these crystals. The value of the parameter a defining the linear rate of growth of F centres in the second stage is also high in additively coloured crystals.The thermoluminescence peak positions and the ratio of the excess concentrations of F centres generated during x-irradiation and the corresponding thermoluminescence areas for the additively coloured and then X-irradiated KC1 crystals are the same as observed earlier by Jain and Mehendru for highly pure KC1 crystals which were not additively coloured prior to x-irradiation.sities, respectively. G7

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Practical applications of the MgB 2 prepared by the in situ method are usually limited because of the pores formed by the volatility of Mg. In order to improve the performance of MgB 2 bulks, MgB 2 bulks were fabricated through an in situ synthesis method with composites of B powder, Mg powder, and 10-100 wt% Mg(BH 4 ) 2 powder. The superconducting properties and grains structure of these MgB 2 bulks were investigated, such as onset superconducting transition temperature (T c ), critical current density (J c ), porosity, resistivity (ρ), and grain connectivity. For the MgB 2 bulk prepared from 80 wt% Mg(BH 4 ) 2 powder added composites, the J c (1 T) value at 5 K was 4.1×10 5 A cm −2 and the onset T c value was 37.5 K. Moreover, the microstructure of these MgB 2 bulks was also analyzed using scanning electron microscope (SEM). The MgB 2 bulk with less pores can be prepared with moderate Mg(BH 4 ) 2 powder added composite as precursor. The composites also provide raw materials for preparing high-quality in situ MgB 2 superconducting wires. Keywords: Mg(BH 4 ) 2 , MgB 2 , composite precursor, porosity, high J c