Emissions and absorption Flashcards
stimulated emission
Emission of photon by atom under influence of an applied EM field, 2 photons rpduced from one incoming photon. outgoing photons have the same phase, frequency and travels in the same direction as the incoming photon
electrical pumping
electrical discharge used to give al the atoms the same energy
optical pumping
put gain medium in the middle of a flash lamp. The lamp flashes and emits photons. into the gain medium, the gain medium absorbs these photons and they get promoted.
cavity
Stores energy, collecting photons to cause even more stimulated emission
3-level laser
ground state is terminal level of lasing transition
excitatino is supplied to populate the pump level -pump transition
pump level decays primarily to the lasing level
lasing level decays to the ground level via radioactive decay
4-level laser
ground state is not the terminal level of the lasing transition
lasing level decays to the terminal level via radioactive decay
Q switching
modyfining the cavity Q by introducing a huge loss (such as covering the mirror. This allows the lasing level of the gain medium to be populated above its normal level when the cavity loss is suddenly reduced, a short intense pulse of radiation is emitted by the laser.
what does thermal equilibrium in the laser cavity mean
means any radiation will be blackbody radiation. Equilibrium is reached when the upward and downward transition rates are equal
A positive gain coefficient is gained by…
pumping electrons from a lower to upper quantum states of laser transition
why is it not possible to pump from level 1 to level 2 directly
stimulated emission rate would approach the rate of pumping
pressure Broadening
THe collision of the other particles with the emitted particle interrupts the emission process
By shortening the characteristic lifetime, this increases the uncertanty in the emitted energy
Inhomogeneous Brodening
eMitting atoms are in different local environments therefore they have a different line profile. The addition of each line profil from all atoms five the total line profile
Natural Broadening
Due to uncertanty principle
Relates lifetime of an excited state to the uncertanty of its energy.
Doppler Broadening
The atoms in a gas emitting radiation have a distribution of velocities. Each photon will be red or blue shifted by the doppler effect.
Depending on the realtive velocities of the atom the observer.
Cavity provides …
Cavity provides the positive feedback that turns an amplifier into an oscillator
