Magneto Optical Kerr effects are generally described macroscopically by dielectric tensor theory [Zak et al (1990)], or the effects can also be described microscopically, where the coupling between the electric field of the light and the magnetisation occurs by the spin-orbit interaction [Daalderop et al (1988)]. In the present work the effects are described less formally, in a pictorial fashion, using the idea of a Lorentz force. To understand the magneto optical Kerr effects, one needs to understand the terminologies associated with the effect, how the state of polarisation of reflected light is dependent upon the initial polarisation and the magneto optical geometry in which it is being used.Light is a transverse electromagnetic wave which can be manipulated optically into plane, circularly or elliptically polarised light (Fig. 2.1). Generally, the plane of polarisation is the plane which contains the electric field E and the direction of propagation. However in some texts [Corson & Lorrain (1970)], the definition of plane of polarisation refers to the plane containing the B field. Any reference to the plane of polarisation in the present work will assume the former definition. If the electric field is polarised in the plane of incidence, it is referred to as p-polarised light as shown in Figure 2.2. Conversely, if the electric field is polarised perpendicular to the plane of incidence, then it is referred to as s-polarised light. The plane of incidence is also known as the scattering plane - the plane which contains the incident and reflected light beam. Circularly polarised light can be further referred to as L-circularly polarised and R-circularly polarised light, where L and R signify the electric field rotating in either a clockwise or an anticlockwise direction with respect to the direction of propagation.
Plane polarised light which is reflected off a metallic surface, is generally elliptically polarised. However if the incident light is either p or s-polarised, then the reflected light will still be plane polarised upon reflection (p or s) [Hecht (1989)]. This is because the reflecting surface is a plane of symmetry for the system. This symmetry is destroyed in the situation where plane polarised light is reflected off a magnetised surface. When p-polarised light is reflected off a magnetic surface, the reflected light has a p-component as in the ordinary metallic reflection but, in addition, a small s-component also appears in the beam. In general, this second electric field component is out of phase with the reflected p-component. This causes the light to become elliptically polarised with its major axis rotated from its initial incident polarisation plane. This magneto optic interaction is shown schematically in Figure 2.3. A similar effect occurs for s-polarised light. The two effects are know as the Kerr ellipticity and the Kerr rotation. As mentioned earlier, the effects are described macroscopically using dielectric tensor theory. In this theory, plane polarised light is viewed as being Therefore the two circular modes travel with different velocities and attenuate differently in the material. Upon reflection from the material, the two modes recombine to produce the Kerr rotation and ellipticity. The macroscopic description of Kerr effects relies on the two modes having different refractive indices within the material. The general form of the dielectric tensor which represents the effects of a magnetic medium is given by [see Zak et al (1990) for details]
Magneto Optical Kerr effects are generally described macroscopically by dielectric tensor theory [Zak et al (1990)], or the effects can also be described microscopically, where the coupling between the electric field of the light and the magnetisation occurs by the spin-orbit interaction [Daalderop et al (1988)]. In the present work the effects are described less formally, in a pictorial fashion, using the idea of a Lorentz force. To understand the magneto optical Kerr effects, one needs to understand the terminologies associated with the effect, how the state of polarisation of reflected light is dependent upon the initial polarisation and the magneto optical geometry in which it is being used.Light is a transverse electromagnetic wave which can be manipulated optically into plane, circularly or elliptically polarised light (Fig. 2.1). Generally, the plane of polarisation is the plane which contains the electric field E and the direction of propagation. However in some texts [Corson & Lorrain (1970)], the definition of plane of polarisation refers to the plane containing the B field. Any reference to the plane of polarisation in the present work will assume the former definition. If the electric field is polarised in the plane of incidence, it is referred to as p-polarised light as shown in Figure 2.2. Conversely, if the electric field is polarised perpendicular to the plane of incidence, then it is referred to as s-polarised light. The plane of incidence is also known as the scattering plane - the plane which contains the incident and reflected light beam. Circularly polarised light can be further referred to as L-circularly polarised and R-circularly polarised light, where L and R signify the electric field rotating in either a clockwise or an anticlockwise direction with respect to the direction of propagation.
Plane polarised light which is reflected off a metallic surface, is generally elliptically polarised. However if the incident light is either p or s-polarised, then the reflected light will still be plane polarised upon reflection (p or s) [Hecht (1989)]. This is because the reflecting surface is a plane of symmetry for the system. This symmetry is destroyed in the situation where plane polarised light is reflected off a magnetised surface. When p-polarised light is reflected off a magnetic surface, the reflected light has a p-component as in the ordinary metallic reflection but, in addition, a small s-component also appears in the beam. In general, this second electric field component is out of phase with the reflected p-component. This causes the light to become elliptically polarised with its major axis rotated from its initial incident polarisation plane. This magneto optic interaction is shown schematically in Figure 2.3. A similar effect occurs for s-polarised light. The two effects are know as the Kerr ellipticity and the Kerr rotation. As mentioned earlier, the effects are described macroscopically using dielectric tensor theory. In this theory, plane polarised light is viewed as being Therefore the two circular modes travel with different velocities and attenuate differently in the material. Upon reflection from the material, the two modes recombine to produce the Kerr rotation and ellipticity. The macroscopic description of Kerr effects relies on the two modes having different refractive indices within the material. The general form of the dielectric tensor which represents the effects of a magnetic medium is given by [see Zak et al (1990) for details]
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