3-11. LASER OPERATION AND USES
a. How does the light amplification by the stimulated emission of radiation (laser)
work? We must obtain a lasing material, an energy source to excite the atoms, a fully
reflecting mirror, and a partially reflecting mirror before we can put our laser into
b. Looking at the figure below (Figure 3-2), we show a laser crystal containing
many atoms in a ground state (white dots) and a few in the excited state (black dots).
The pumping light, or energy source (wavy arrows in A), raises most of the atoms to the
excited state, creating a population inversion--that is, more atoms in the excited state
than the ground state.
A - Pumping light raises many atoms to excited state.
B - Lasing begins when a photon is spontaneously emitted along the axis of the
crystal. This stimulates other atoms in its path to emit.
C - The resulting wave is reflected back and forth many times between the ends of
the crystal and builds in intensity until finally it flashes out of the partially silvered
Figure 3-2. Sequence of operations in a solid crystal laser.