Permanent-magnet Faraday isolator with the field intensity of more than 3 tesla

Abstract

A permanent-magnet system with a maximum magnetic field exceeding 3 T, which is a record value for Faraday isolators, has been created. The magnitude of the field in the system is close to the theoretical limit that can be achieved at an optimal magnetization distribution. This is possible thanks to the use in the central area of the system of magnetic conductors that possess a saturation induction higher than the residual induction of the strongest magnets and provide more optimal magnetization distribution than magnets. But the main feature of the system is control of demagnetizing fields in the center of the system by optimizing the position and shape of magnetic conductors, thus retaining the maximum volume of the magnets in the core of the system without the risk of their magnetization reversal. The technology of controlling demagnetizing fields by means of magnetic conductors is proven for the first time. The created system is promising for the development of Faraday isolators for high-power lasers as it allows decreasing the length of the magneto-optical element and reducing parasitic heat generation. Record results on the maximum permissible operating power of Faraday isolators based on CeF3 and TSAG crystals were obtained with the use of this system. It is also promising for the development of Faraday isolators for ‘eye-safe’ and mid-infrared radiation since the Verdet constant of magneto-active crystals in these wavelength ranges reduces substantially compared to the near-infrared. The creation of strong magnetic field becomes of principal importance for providing a needed angle of Faraday rotation.