In this work, the effect of storing time on the variation of surface and volume resistance of the 10 MeV electron beam irradiated LDPE and HDPE samples was investigated. This study was carried out about one month after irradiation. The samples were prepared in sheet form with thickness of 2 AE 0.1 mm and irradiated at the doses of 70 to 370 kGy. All the samples were kept at room temperature. The results show a peak at about 25 days after irradiation in surface resistance for all the samples. The volume resistance measurements did not show any significant variation.
Cross linking of the HDPE was performed with high energy electron beam. EPR spectroscopy was used to study the life time of unpaired electron in the irradiated samples. Dielectric constant and dielectric strength almost remained unchanged but, volume resistively and dissipation factor increased and decreased respectively, after irradiation. The results shows that the dissipation factor is going to be recovered slowly with the storing time at room temperature. It is believed that variation of some electrical properties during time after irradiation are due to the effects of free radical and charge trapping remained in the bulk of material.
In this paper, the Gaussian, Lorentz and Lorentz-Gaussian beams are used as the pump beam in a diode side pumped Nd:YAG leaser and the effects of these beams on the absorption efficiency of the laser are investigated. It is illustrated that the absorption efficiency for Lorentz-Gaussian profile is higher than the two others. Also has been shown that for entrance Lorentz-Gaussian profile, the absorption efficiency is increasing with decreasing the distance from the diodes to the slits and increasing the diameter of the laser rod. It is shown that there is an optimum slit width corresponding to the maximum absorption efficiency for any laser diode side-pumped solid-state lasers.
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