Rare earth doped gain media
Rare earth ions doped in the dielectric materials seem to be ideal
quantum-dots with much smaller size than those of artificial quantum dots
made of semi-conductors. Therefore, rare earth trivalents can act as
eminently effective luminous ions in laser gain media.
The advantage of the rare-earth trivalent as a luminous ion
Narrow emission bandwidth
Narrow bandwidth is due to the small interaction with other electrons in
dofferent energy level/ the crystal field/ lattice vibrations. This narrow
bandwidth enables stored energy inside laser gain media to be effectively
connected to the laser output.
Long lifetime of the excited state
Since the dipole transition between laser upper and lower level is parity
forbidden, the lifetime of excited states in rare-earth trivalent is 1,000
- 1,000,000 times longer than other luminous materials.
Large radiative quantum efficiency
Dielectric shielding by 5s/5p octet around HOMO consisted by 4f-electrons
suppresses the quenching and diffusion processes caused by the interaction
to other rare-earth trivalent. As a result of this suppression, the energy
leakage from laser gain media become weakened.