Use of mechanical stress in design of a Faraday isolator for high power radiation

Abstract

Summary form only given. Many laser applications require propagation of high power radiation through transmissive optical elements such as Faraday isolators. Absorption of laser radiation in the optical element leads to not only thermal lensing but also self-induced depolarization, resulting in a limitation of the maximum isolation ratio. The spatial nonuniform distribution of temperature causes two effects contaminating laser polarization: temperature dependence of the Verdet constant and linear birefringence due to the photoelastic effect of thermal stress. The last phenomenon is more efficient for most magneto-optical materials and hence limits the isolation ratio. In order to suppress the absorption induced depolarization, we have developed a method in which we apply force to induce stress into a magneto-optical sample. The direction of stress is maintained (in contrast to thermal stress) over the entire cross-sectional area. Due to the photoelastic effect, the induced stress leads to linear birefringence with a uniform direction of eigenpolarizations (they are along x and y axes) and various phase delays between them.