تم دراسة المرنانات غير المستقرة في المنظومة الليزريه بشكل عام والتركيز على أحد المشاكل التي يواجهها هذا النوع من المرنانات وهي تأتيرات الحيود. فرغم ان هذه الظاهرة تعتبرالوسيله التي يخرج عن طريقها الشعاع من المنظومه الليزريه الا انها تسبب في فقدا كبيرا في قدرة الشعاع الليزري الخارج . احدي الطرق المقترحه للتقليل من تاتيرات الحيود السلبيه في هذه الحاله هو احدات تدرج في المرآه , فقد تم في هذا البحث مقارنة نتائج متقاربه وعليه تم استنباط معادلة خاصه بالحيود عبر مرآة بتدرجين وحساب القيمة الذاتية للشعاع الليزري الخارج وتحدي مدي التحسن في التقليل من الخسارة الناتجه من خلال التغير في قيمة عدد فرنيل وذلك بمقارنة العلاقات البيانية لمرآة عادية ومرآة بتدريج واحد وبتدرجين للمرنان نفسه , و تم أيضا دراسة تاثير القيمة الذاتية بعرض الدرجة في المرآة وعرض المنحنيات الخاصة بها . Abstract Unstable resonators in laser systems have been studied in general and the focus was on one of the problem facing this type of resonators namely the effect of diffraction .although diffraction Is the mean to get the laser rays out of the system, it causes major loss of power in the output If it is treated adequately. One of the suggested method to reduce the negative effect of diffraction is to make a gradual step on the output mirror. a comparison has been made between the results for a single step mirror with result from previous study . the two results agreed with each other to an acceptable range . an equation for a two-step mirror was derived and the Eigen Values of the outgoing laser beam were calculated . the amount of improvement in the output power was calculated by changing the value of Fresnel number and comparing the situation for an ordinary mirror , single step mirror and two-step mirror. The results show good improvement for the two-step mirror. also the dependence of the step with on the eigen value was studied. We can conclude from the current work that by introducing certain step width specific width could improve the output power from unstable resonators by minimizing the negative diffraction effect. The amount of improvement seems to increase with increasing number of steps. For future work we suggest that more exact methods to calculate the eigen values, such as proni method, should be tried and the effect of the output mirror tilt must be taken into account.
سهير محمود احمد ابو حجر (2001)

This paper, emphasis different growth techniques of two-dimensional hole gas of strained germanium (sGe) heterostructure, molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). sGe heterostructure has become an important material as a replacement material to Silicon in P-type devices because of its higher hole mobility and lower effective mass. Researchers study this material in terms of electrical and spintronic devices according to technology demands for devices with higher efficiency and low power consumption. High hole mobility up to 1×10cm/Vs at temperature of 1.5 K has been reported for normal structure declaring high quality samples with low density dislocation and low interface roughness. arabic 14 English 105
Adel Diyaf, A.H. A. Hassan , U. Elfurawi , A. E. Abubkr (6-2019)

Thin films of cobber doped ZnO have been prepared on glass substrate using the Sol-Gel spin coating technique. The effect of doping percentage of Cu to ZnO thin films on the optical properties and optical constants are concluded from absorption and transmission measurements which are obtained by using double beam UV-Visible 1800 spectrophotometer in the wavelength (300-800)nm. It was found that the transmittance increases with increasing the doping percentage (0.01, 0.02,0.03 and 0.04)mol%, while the Absorbance is decreased. The optical energy band gaps have been evaluated and their values seem to be decreased by increasing the doping concentration level in the range (0.01, 0.02, 0.03)mol% followed by a rise with increasing the doping level to 0.04mol%. arabic 17 English 84
Fawzeia Khamis(9-2020)