LIGHT-MATTER INTERACTION
Einstein's Law of Radiation
ABSORPTION
light intensity spectral density
in J/m2
Absorption process
Note: We will see below, when stating the equilibrium rate, why we
have to consider Pnm as a probability per unit time.
EMISSION
Einstein suggested there should be two types of emission
processes
Spontaneous Emission
Stimulated Emission
probability per second
to the light intensity spectral density I(ω)
per second
emission probability per second
Equilibrium Conditions
[ Number of atoms
per second ]
[ Numbers of atoms
per second ]
Rate at which atoms transit
from the energy level m to
the energy level n.
Has to be in units of sec-1
light intensity
spectral density I(ω)
light intensity
spectral density I(ω)
stimulated