كليدواژه :
فيبر ليزر , بلور ايتربيم:ياگ , چهارهسته , دمش طولي , آناليز حرارت - سازه
چكيده فارسي :
هدف اين نوشتار بررسي رفتار ترمومكانيكي يك فيبر ليزر تك‌غلافه‌ي ايتربيم:ياگ (Yb:YAG) تحت دمش طولي پيوسته است. بدين منظور فيبر به دو صورت تك‌هسته‌يي و چهارهسته‌يي مدل‌سازي شده و در محيط نرم‌افزاري المان محدود شبيه‌سازي مي‌شود. براي تعيين توزيع دما و تنش در بلور، به دليل تقارن در بار حرارتي و هندسه، مدل يك‌چهارم به كار رفته است. از آناليز ميدان‌هاي كوپله‌ي حرارت ـ سازه در محيط نرم‌افزاري بهره گرفته شده و ابتدا توزيع دما در بلور محاسبه و سپس ميدان تنش در دو فيبر تك‌هسته‌يي و چهارهسته‌يي تعيين مي‌شود. نتايج نشان مي‌دهد كه در يك توان مشخص، فيبر چهارهسته‌يي نسبت به فيبر تك‌هسته‌يي بيشينه تنش كوچك‌تري دارد و توان دمشي شكست آن به مراتب بزرگ‌تر از فيبر تك‌هسته‌يي است. در نهايت، آثار حرارتي دمش شامل عدسي شدگي در دو بلور چهارهسته‌يي و تك‌هسته‌يي با هم مقايسه شده و نشان داده مي‌شود كه از نظر ترمومكانيكي فيبر چهارهسته‌يي عملكرد مناسب‌تري دارد.
چكيده لاتين :
The solid state lasers consist of host mediums that are doped by an active ions. The host environment is built in the form of slab, rod, disk and fiber according to the geometric shape. In most cases, the solid lasers can be stimulated by diode pumping. During the pumping, some of the pumping energy at the crystal is converted to heat and this heat causes the temperature gradient in the crystal. The temperature gradient can produce thermal stresses and even lead to fracture in the crystals. In the fiber lasers, these phenomena disturb the laser operation and decrease the maximum input power of the laser. In this paper, the thermo-mechanical behavior of single clad Yb:YAG fiber laser is discussed under continuous end pumping. The single clad fibers have been modeled with single and four cores and they are simulated by finite element software (Ansys). Since the thermal loading and geometry of the fiber have symmetry planes, in the modeling, one quarter model is used to determine the temperature and stress distributions. In the Ansys software, the coupled thermal-structural analysis is utilized. First, the temperature distribution is calculated in the thermal environment of the software and then thermal stress fields for single core and four-core fiber lasers are obtained by applying the temperature distributions calculated through the thermal analysis. In the analysis, the mesh dependency is evaluated and for achieving convergence, the required number of element is determined. The temperature distributions in single and four core fibers, with two positions for cores, are calculated. For any case, the calculated temperatures are compared with each other and the position of core related to smaller temperature is selected. The results show that, in comparison to single-core fiber, a four core fiber has smaller maximum stress at the same power and higher pumping fracture power. Finally the other thermal effects of the pumping, including thermal lensing, for single and four core fiber are compared with each other and it is shown that the four core
fiber laser has better performance in terms of thermomechanical output.
