Some Explorations in Magneto-Optics and
Opto-Magnetics
مقناطیسی نوریات اور نوری مقناطیسیت
کے چند گوشے
Dr. Ali Akbar
Magneto-optic effects are manifestations of light-matter interaction and their role in development of modern technology is central. From the discovery of the Faraday effect and the Kerr effect to the development of devices for optical isolation, optical modulation, polarization control and nonreciprocal phase-shifters manifest the overarching role of these physical phenomena in different forms. The change in optical response of a medium in the presence of magnetic field is referred to as magnetic birefringence, ascribed to the asymmetry and anisotropy introduced by magnetic field. The induced birefringence results in the rotation of the plane of polarization of the incident polarized light and association of ellipticity to the light coming out of the magnetically active medium. Depending on the relative orientation between applied magnetic field and propagation vector, magnetically induced birefringence phenomena are categorized as circular and linear birefringence.
In this presentation, we’ll set forth the discussion with the phenomenological description of these asymmetries—the various forms of birefringence and intermixing of these effects. Magnetic birefringence effects are miniscule and require phase sensitive detection. We’ll also present several experimental techniques which have been devised, designed and implemented in order to quantify these asymmetries.
With technological advancement in femtosecond laser technology, the conventional role of magneto-optics has been widened from probing to controlling the magnetization of magnetic systems. This is dubbed as opto-magnetics. In this context, all-optical deterministic magnetization switching for rare earth-transition metal (RE-TM) alloys and magnetic nano-structures in the form of bilayers, core shell and alloys is simulated, when excited with femtosecond laser pulses.
Finally, we explore the mainstream magneto-optic effect (The Faraday effect) in the quantum realm which requires special tools and skills in order to get realized in an experimental setting. The Faraday rotation for quantum light encompasses the generation of single photons through spontaneous parametric down-conversion and state estimation by quantum state tomography. The tomographic results are then analyzed and various kinds of minimization algorithms are adopted to extract Faraday rotation angles. The extracted Faraday rotation angles from the estimated state are corroborated with the previous experimental findings. The trajectories are also mapped as rotations with tilted axes on the Bloch sphere. The position of the axis of rotation yields ellipticity of the single photon’s quantum state.
