Terahertz time-domain spectroscopy was used to make experiment and investigation for the characteristics of high quality 0.3BaSrTiO3-0.7NdAlO3 ceramics in the terahertz range, which was made by the solid state reaction method. The frequency resolution of experiment system was 4.5 GHz, and all-solid-state 532nm laser was used as external optical pump, which obliquely incidence on the surface of the sample at the angle of 45°. From the experiment that when the external optical pump’s intensity increased from 0 mW to 300 mW at room temperature, the 0.3BaSrTiO3-0.7NdAlO3 ceramics’ transmission waveform time shifts could be obviously observed, and with the increasing power of pump laser, the absorption coefficient could be modulated, the modulation range varied from 21.38 cm-1 to 13.77 cm-1 and the modulation depth nearly reached up to 36% at 0.55 THz. Further analysis showed that the micro-mechanism of absorption coefficient modulation with the intensity of external optical pump was attributed to the internal space charge field in the 0.3BaSrTiO3-0.7NdAlO3 ceramics caused by the excited free carriers. The experiment and analysis proved that the 0.3BaSrTiO3-0.7NdAlO3 ceramics have higher tunability, lower dielectric loss and good temperature stability in THz range, which will have good reference value and wide application for communication in THz range.
In order to improve manufacture quality and machining efficiency, this paper studies the technology of rectangular flat-topped beam. Flat-topped beam can effectively reduce the region of heat affected zone. Rectangular beam can reduce overlap rate. So, it is very important to convert the circular Gaussian beam to rectangular flat-topped beam. The fiber laser has been widely used to laser manufacture Industry at this present. The fiber has better coupling capability with laser spot. We choose double-cladding fiber to acquire uniform rectangular beam. Laser beam transmission model was created up with RP fiber power soft. We also make the model of the double-cladding fiber. When the Gaussian beam is transmitting along fiber, high-order mode lights appear and mixture with each other. Because the double-cladding fiber has central-dip profile index, the energy transfers from central to edge. The results show that the double-cladding fiber can be used to improve the uniformity of transmitting beam. When the shape of fiber core is rectangular and the chamfer is circle arc work, we can get rectangular uniformity beam.
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