In direct-drive laser fusion, the sufficient uniformity of focal spot for realizing high efficient compression and central ignition is required. However, the laser beams are difficult to achieve sufficient uniform for compressing the shell symmetrically inward. We proposed a novel scheme to achieve controllable focal length based on electro-optic effect. The electro-optic crystal was placed in the front of the laser fusion system and applied the electro field with approximate spherical distribution. Since the wavefront of laser beam is transformed through the electro-optic crystal, the focal spot of the transformed laser beam would be changed on the target. Theoretical analysis and numerical simulation have been made, and the results show that the proposed scheme could achieve enough controllable focal spot on the target.
Semiconductive ceramic humidity sensors based on ZnO2 * SiO2 * P2O5 doped with Y2O3 and Nb2O5 are prepared by the solid phase reaction at high temperature. Y2O3 and Nb2O5 change ZrO2 character from an isolator to N- and P-type semiconductor separately. The Y2O3-, Nb2O5- and non-doped samples have extremely different total resistance at the room temperature and a certain relative humidity. The former is far less than the later. By means of X-ray diffraction, Fourier infrared absorption and Raman backward scattering spectra, the microstructure of ZrO2 grain in non-doped and Y2O3- or Nb2O5-doped samples are known to belong respectively to monoclinic and tetragonal symmetrical crystal systems. On the basis of the standard absorption peak sites, four fundamental phonon energies of ZrO2 are calculated: TO equals 0.0457, LO equals 0.0365, TA equals 0.0069, LA equals 0.0249 ev. All the Fourier infrared absorption speaks of ZrO2 in each and every ZrO2 * SiO2 * P2O5 humidity sensor consist of two or more out of the four elementary phonons in different combinations. Any and every Raman backward scattering peak of ZrO2 is made up of two or more out of these phonons too.
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