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Title: Relation between magnetization and Faraday angles produced by ultrafast spin-flip processes within the three-level Λ-type system

Ultrafast magneto-optical (MO) experiments constitute a powerful tool to explore the magnetization dynamics of diverse materials. Over the last decade, there have been many theoretical and experimental developments on this subject. However, the relation between the magnetization dynamics and the transient MO response still remains unclear. In this work, we calculate the magnetization of a material, as well as the magneto-optical rotation and ellipticity angles measured in a single-beam experiment. Then, we compare the magnetization to the MO response. The magnetic material is modeled by a three-level Λ-type system, which represents a simple model to describe MO effects induced by an ultrafast laser pulse. Our calculations use the density matrix formalism, while the dynamics of the system is obtained by solving the Lindblad equation taking into account population relaxation and dephasing processes. Furthermore, we consider the Faraday rotation of the optical waves that simultaneously causes spin-flip. We show that the Faraday angles remain proportional to the magnetization only if the system has reached the equilibrium-state, and that this proportionality is directly related to the population and coherence decay rates. For the non-equilibrium situation, the previous proportionality relation is no longer valid. We show that our model is able to interpretmore » some recent experimental results obtained in a single-pulse experiment. We further show that, after a critical pulse duration, the decrease of the ellipticity as a function of the absorbed energy is a characteristic of the system.« less
Authors:
 [1] ;  [2]
  1. Departamento de Física e Astronomia, Instituto de Física dos Materiais da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal)
  2. Departement of Ultrafast Optics and Nanophotonics, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS, Université de Strasbourg, 23, Rue du Loess, BP 43, 67034 Strasbourg-Cedex 2 (France)
Publication Date:
OSTI Identifier:
22494687
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DENSITY MATRIX; EQUATIONS; FARADAY EFFECT; LASER RADIATION; MAGNETIC MATERIALS; MAGNETIZATION; MAGNETO-OPTICAL EFFECTS; PULSES; RELAXATION; ROTATION; SPIN FLIP