L2 Flashcards
Artificial Crystals
- Artificial crystals for optical frequencies behave like natural crystals at X-ray frequencies.
- Key approximation: light at optical frequencies has a much longer wavelength than the inter-atomic spacing.
Bound / Free Charges / Currents
- Bound charges: immobile (core electrons and localized valence electrons).
- Free charges: charges that can move.
- Bound currents: small current loops (intrinsic spin, orbital angular momentum).
- Free currents: macroscopic currents (current in a copper wire).
Polarization Density
context? meaning?
- Introduce electric flux density D (displacement field)
- define polarization density P
Magnetization Density
change / add context
New magnetic field vector H and definition of magnetization density. Rewritten curl equation, removing explicit dependence on bound currents.
Macroscopic Approximation
what does it approximate and how?
- Approximate free charge/current as average over the cube volume.
- Bound charge/current approximated as boundary effects.
Assumption 1
Context!
- P depends on E
- M depends on B
- Good in most cases, but not when magnetoelectric coupling is significant.
Assumption 2
- P and M depend on local values of E and B.
- Equivalent to the long wavelength assumption.
Assumption 3
add to combined card
- Dependence of P and M on E and B is not location-dependent (homogeneity).
- Easily corrected with boundary conditions.
Assumption 4
add to list of assumptions, then delete
- P and M depend on immediate values of E and B (dispersionless).
- Often invalid, but repaired using dispersion.
Assumption 5
add to combined card
- P and M are linear in E and B (linearity)
Assumption 6
make a card with a list of all the names of assumptions
P and M are in the same or opposite direction as E and B (isotropy).
Laser in sugar solution
Laser light passes through a sugar solution. The gradient in refractive index causes curvature of the light beam.
Refractive Indices
Representative refractive indices (@20℃):
- Vacuum: 1
- Air: 1.00027
- Water: 1.33
- Silicon: 3.48 (1550nm)
Plane Waves
Wave equation is linear. Linear combination of plane wave solutions is also a solution. E and B lie in a plane normal to the direction of propagation k (TEM).
Optical Impedance
In vacuum, Z0 = 377 Ω. This gives the amplitude ratio between electric and magnetic fields in an EM wave.
Linear Polarization
Electric field points either parallel or antiparallel to a fixed direction.
Polarization Effects
Polarization affects reflection, absorption, and scattering of light. Optically active materials rotate the polarization plane of linearly polarized light.
Light Absorption
Green light is absorbed more strongly by a red balloon than by a transparent or green balloon.
Energy Transport by Light
Light transports energy. Examples include laser machining and two-photon polymerization.
