چكيده به لاتين
High-power and high-efficiency lasers are very important in military and industrial applications. Some physical phenomena including scattering, Aerosols/moleucules absorption, turbulence due to air density fluctuations and thermal blooming affecting high-power laser beams propagation through atmosphere are investigated. In this thesis, method of incoherent beam combining for fiber laser is presented which is based on spectral and lens array combining. Regarding the propagation of optical/IR wave through random media such as atmospheric turbulence, to describe amplitude and phase fluctuations of the field, a brief review on theorical methods based on the scalar wave equations solution is presented. Parameters of single-mode and multi-mode laser beams such as intensity, spot size and propagation efficiency at the target are formulated and laser beam propagation are studied and analyzed by MATLAB programming software.
Finally, laser parameters such as spot size, peak intensity and propagation efficiency at the target in coherent and incoherent beam combining are investigated and compared in various turbulence conditions. The results demonstrate that the behavior of beam propagation in incoherent beam combining is very close to coherent method in moderate to strong turbulence levels. Therefore, incoherent beam combining can be used instead of coherent method in many applications due to problems and technical complexities in coherent beam combining. By investigation of beam quality factor effect in propagation of incoherent combined beam, it was shown that in moderate to strong turbulence, using very good beam quality is not essential.
Keywords: fiber laser, thermal blooming, atmospheric turbulence, incoherent beam combining, lens array
