c

velocity of light in free space

D

displacement vector

d _mn

Kleinman s d-coefficient

E

electric field in lightwave

complex amplitude of electric field

e

electronic charge

f

oscillator strength

Planck s constant

I

intensity of lightwave

k

propagation vector

m

mass of electron

N

number of equivalent harmonic or anharmonic oscillators per volume

n _1,2

index of refraction at the fundamental and second-harmonic frequencies, respectively

P

macroscopic polarization

P ^{( n )}

nth-order macroscopic polarization

P _0,2,+,?

power of lightwave at the fundamental, second-harmonic, sum-, and difference-frequencies, respectively

complex amplitude of macroscopic polarization

Q

amplitude of vibrational wave or optic phonons

S

strain of acoustic wave or acoustic phonons

T _mn

relaxation time of the density matrix element ? _mn

? j

damping constant of jth optical transition mode

?

Miller s coefficient

?( E)

field-dependent optical dielectric tensor

? _n

nth-order optic dielectric tensor

? ₀

optical dielectric constant of free space

?

amplitude of plasma wave or plasmons

?

wavelength

? _mn

density matrix element

?( E)

field-dependent optic susceptibility tensor

? ₁ or ?(1)

linear optic susceptibility tensor

? _n or ?( n)

nth-order optic susceptibility tensor

? _p

plasma frequency

dipole moment between states a and b