Chapter
2 Optics of Gaussian Beams
2.1. Definitions and Basic Properties
2.1.2. Fourier transform of the beam profile
2.2. Gaussian-beam Propagation in Free Space
2.4. Effect of Lens on Gaussian Beam
2.4.2. Numerical aperture, spot size at focus, and depth of focus
3.1. Stationary-phase Approximation
3.2. Application of Stationary-phase Method to Diffraction Problems
3.3. Near-field and Far-field Diffraction
3.4. Diffraction in the Presence of a Lens
3.4.1. Primary aberrations
3.5. Vector Effects in Diffraction
4 Diffraction of Gaussian Beams from Sharp Edges
4.1. Formulation of the Problem
4.2. Diffraction from Knife-edge
4.3. Diffraction from 180° Phase-step
4.4. Diffraction from 90° Phase-step
4.5. Detecting Phase-steps by Spatial Matched Filtering
5 Optics of Thin Films and Multilayers
5.1. Notation and Formalism
5.2. Maxwell's Equations and Plane-wave Propagation
5.3. Plane Wave in an Isotropic Medium
5.4. Reflection at the Interface of Free Space and an Isotropic Medium
5.5. Reflection at the Interface of Free Space and a Birefringent Medium
5.6. Reflection at the Interface of Free Space and a Magnetic Medium;the Magneto-optical Kerr Effect
5.7. Plane Wave in Medium with Arbitrary Dielectric Tensor
5.8. Boundary Conditions at the Interface between Adjacent Layers; Iterative Formula for Computing the Reflectivity of Multilayers
5.9. Plane-wave Transmission Through Multilayers
5.10. Power Computation using Poynting's Theorem
Appendix 5.A. Transformation of Dielectric Tensor under Rotation of Coordinates
Appendix 5.B. Method of Computing the Roots of Fourth-order Polynomials
6 Magneto-optical Readout
6.1. States of Circular, Linear, and Elliptical Polarization
6.2. Quarter-wave Plate (QWP)
6.3. Polarizing Beam-splitter (PBS)
6.4. Differential Detection Scheme and Magneto-optical Readout
6.4.1. Effect of retardation plate
6.5. Wavelength-dependence of Polar Magneto-optical Kerr Effect
6.5.2. Mathematical analysis
6.5.3. Results and discussion
6.6. Edge Detection using Diffraction from Domain Walls
6.7. Figure of Merit for Magneto-optical Media
7 Effects of High-numerical-aperture Focusing on the State of Polarization
7.1. Focused Beams, Oblique Rays, and Polarization Conversion
7.2.1. The case of a perfect reflector
7.2.2. The case of a front-surface aluminum mirror
7.2.3. Thin dielectric layer on a glass substrate
7.2.4. Magneto-optical film with a dielectric coating
7.2.5. Quadrilayer magneto-optical disk
7.2.6. Plastic substrate and the effects of birefringence
7.3. Summary and Conclusions
8 Computer Modeling of the Optical Path
8.1. Collimation and Focusing of the Laser Diode Beam
8.1.1. Effect of beam profile on the focused spot
8.2. Diffraction Gratings and Grooved Optical Disks
8.2.1. Near-field and far-field patterns of gratings
8.2.2. Reading preformat and track information from grooved disk
8.3. Analysis of Focus-error Detection by the Astigmatic Method
8.3.1. The acquisition range
8.3.2. Diffraction analysis
8.3.3. Push-pull tracking, track-crossing signal, and feedthrough
8.4. Analysis of Focus-error Detection by a Ring-Toric Lens
8.5. Diffraction Effects in Magneto-optical Readout
8.5.1. Magneto-optical readout by differential detection
8.5.2. Magneto-optical readout by diffraction from domain walls
9 Noise in Magneto-optical Readout
9.1. Noise in the Electronic Circuitry
9.2. Shot Noise in Photodetection
9.2.1. Spectral analysis of shot noise
9.2.2. Dark-current noise
9.4. Noise due to Disk Reflectivity Fluctuations and Depolarization
9.5. Jitter and Signal-amplitude Fluctuations
9.5.1. Effects of finite beam size on signal and noise spectra
10 Modulation Coding and Error Correction
10.1. Preliminary Remarks
10.2. The State-transition Table
10.3. The Trellis Diagram
10.4. Encoding and Decoding Algorithms
10.5. Burst-error Correction
10.7. Random-error Correction
10.8. Numerical Results and Discussion
11 Thermal Aspects of Magneto-optical Recording
11.1. The Heat Diffusion Equation
11.1.1. Heat diffusion in one-dimensional space
11.1.2. Heat diffusion in two-dimensional problems with circular symmetry
11.1.3. A three-dimensional heat diffusion problem
11.2. Numerical Solution of the Heat Diffusion Equation
11.2.1. The implicit method of solving linear partial differential equations
11.2.2. The alternating-direction implicit technique
11.2.3. Extension to moving media
11.3. Light Absorption and Heat Diffusion in Multilayers
11.3.1. Thermal engineering of the media
12 Fundamentals of Magnetism and Magnetic Materials
12.1. Magnetic Fields in Free Space
12.1.1. Units of electric charge
12.1.3. H-field and B-Field
12.1.4. Vector potential A
12.2. Current Loops and the Magnetic Dipole Moment
12.2.1. Angular momentum of a current loop
12.2.2. Torque on a current loop in a magnetic field
12.2.3. Larmor precession
12.2.4. Force on a current loop in a magnetic field
12.2.5. Equivalence of current loops and slabs of magnetic material; relation between B, H and M
12.3. Larmor Diamagnetism
12.4. Ground State of Atoms with Partially Filled Shells - Hund's Rules
12.4.1. Spectroscopic splitting factor
12.5.1. Langevin paramagnetism of a collection of identical atoms
12.5.2. Conduction electron (Pauli) paramagnetism
12.6. Exchange Interaction
12.6.1. The Heisenberg model
12.6.2. Exchange stiffness coefficient
12.7.2. Antiferromagnetism
12.8. Electronic Structure and Magnetic Properties of the Rare Earths
12.9. Transition Metals of the Iron Group
12.10. Magnetic Anisotropy
12.10.1. Single-ion anisotropy
12.10.2. Anisotropy by pair-ordering
12.10.3. Shape anisotropy
12.10.4. Anisotropy due to classical dipole-dipole interactions
13 Magnetostatics of Thin-film Magneto-optical Media
13.1. Domain Walls in Perpendicular Films
13.1.1. Domain-wall energy density
13.1.2. Effect of demagnetizing field; Bloch and Neel walls
13.2. Mathematical Analysis of Stray and Demagnetizing Fields
13.2.1. Computation of H-field from the vector potential
13.2.2. Averaging the H-field through the film thickness
13.2.3. Energy of demagnetization
13.2.4. Field computation on the hexagonal lattice
13.3. Micromagnetics of Circular Domains
13.3.1. External field energy
13.3.2. Anisotropy energy
13.3.4. Demagnetizing energy
13.4. Measurement of the Energy Density of Domain Walls
14 Mean-field Analysis of Amorphous Rare Earth-Transition Metal Alloys
14.1. The Mean-field Model
14.1.1. Computing the Curie temperature
14.2. Comparison with Experiment
14.3. Single-ion Anisotropy and the Mean-field Model
14.4. Exchange Stiffness Coefficient
14.5. Macroscopic Anisotropy Energy Constant
14.6. Domain Wall Characteristics
15 Magnetization Dynamics
15.1. Magnetization Dynamics for a Lattice of Interacting Dipoles
15.1.1. Effective magnetic field
15.1.2. The Landau - Lif shitz - Gilbert equation
15.1.3. Energy considerations
15.2. Domain Wall Structure and Dynamics; Analytic Treatment
15.2.1. Static domain wall equations
15.2.2. Structure and energy density of straight walls
15.2.3. Structure and energy density of circular walls
15.2.4. Domain walls and the effect of the demagnetizing field
15.2.5. Wall motion caused by a perpendicular magnetic field
15.2.6. Doring mass and Walker breakdown
15.3. Computer Simulations
15.3.2. Structure and dynamics of simple walls
15.3.3. Nucleation coercivity and effects of random anisotropy
16.1. The Stoner-Wohlfarth Theory of Magnetization Reversal
16.2. Nucleation Coercivity
16.2.1. Dependence of coercivity on cone angle
16.2.2. Dependence of Hc on the strength of exchange
16.2.4. Resident reverse-magnetized nuclei
16.2.5. Weakly anisotropic defects
16.2.6. Defects with tilted easy axis
16.3. Coercivity of Domain Wall Motion
16.3.1. Walls and random-axis anisotropy
16.3.2. Motion of domain walls
16.3.3. Wall coercivity and patch-to-patch random anisotropy
16.3.4. Pinning of domain wall by voids
16.3.5. Lattice with in-plane defects
16.3.6. Isolated or weakly coupled patches
16.3.7. Patches with different anisotropy constants
17 The Process of Thermomagnetic Recording
17.1. Facts and Observed Phenomena
17.2. Magnetostatic Model of the Recording Process
17.3. Dynamic Simulation of the Recording Process
17.3.1. The LLG equation for the strongly coupled ferrimagnet
17.3.2. The simulation algorithm
17.3.3. Temperature profile and material parameters
17.3.4. Observations concerning the nature of nucleation
17.3.5. Simulation results and discussion
17.4. Exchange-coupled Magnetic Multilayers
17.4.1. Magnetic capping layer for lowering the write/erase field
17.4.2. Direct overwrite in exchange-coupled multilayer
17.4.3. Magnetically induced super resolution (MSR)
18 Media Characterization
18.1. Magnetic, Magneto-optical and Galvanomagnetic Measurements
18.1.1. Magnetoresistance and the Hall effect
18.1.2. Measurements on Co/Pt sample
18.1.3. Measurements on Tb28Fe72 sample
18.1.4. Measurements on Tb24Fe76 sample
18.2. Polarized-light Microscopy
18.2.1. Observations and discussion
18.3. Lorentz Electron Microscopy
18.3.1. Mathematical analysis
18.3.2. Numerical results and discussion
18.4. Magnetic Force Microscopy (MFM)
18.4.1. Experimental observations
18.4.2. A model for the needle in MFM and the method of force calculation
18.4.3. Results of numerical simulations
The Physical Principles of Magneto-optical Recording
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