Reading Quiz For a conductor which quantity is set to zero in last time’s Lorentz oscillator model? decay frequency, wD resonance frequency, w0 light frequency, w reflection frequency, wR

Reading Quiz The vector that gives the direction of energy transfer through space in an E-M wave is called the: Clausius vector flow vector Michelson vector polarization vector Poynting vector

Index of refraction

Common optical glass indices vs wavelength

Hint: what would these curves look like in the limit of N  0? P3. If we increase the density of a gas (N), index n a) increases for all w b) decreases for all w c) increases with density below resonance, decreases above d) decreases with density below resonance, increases above Hint: what would these curves look like in the limit of N  0?

P6. In a glass that absorbs green light the index , imaginary index k is greatest for ______ (same choices) yellow green blue P4. In a glass that absorbs green light best, the real index n is probably greatest for ______ light. yellow green blue

Last time: optical properties of spring-like oscillating dipoles: dielectric (i.e. insulator)

Optical properties of a conductor Why do metals reflect so well? If there’s no damping, how to they respond to a steady E-field? A What will their motion be in an oscillating field?

Optical properties of a conductor We can start with the math done for dielectric (insulator): A …and modify for free electrons:

Optical properties of a conductor Case of very little damping g<<w: For w< wp , check the sign of . Which must be nonzero? n b) k

Complex index, dielectric constant, k g=0 n, k A What does n = 0 mean here? For dielectric, k creates absorption. For metal, k creates strong reflection

n,k for metal. Plasma frequency divides two regimes g=wp/10 g=0 n, k A Which frequencies are transmitted well? Which are reflected well?

Typical plasma frequencies   density N (m-3) (Hz) metals 1028 1016 semicond. (pure) 1024 1014 semicond. (doped), fusion expts 1020 1012 ionosphere (60 to 450 km) 1011 107 interplanetary space 105

Reflectance vs. Wavelength Plasma frequency of silver

Poynting Vector energy density in a vacuum Its magnitude is the intensity: Power/area What equation in this course does this look like? So S is an energy flow vector: energy/area/time

For a plane wave in index n, derive the time average intensity S or intensity For a plane wave in index n, derive the time average intensity From Maxwell Eqns

Directions of vectors The following are always true:! (definition and Maxwell eqn for plane wave) Which vector pair is not guaranteed to be perpendicular? E, S E, k E, B S, B B, k

Preview of a birefringent crystal