The broadband optical pumping of a synthetic pink ruby crystal using a flash lamp
is capable of raising a substantial fraction of the chromium ions to the upper laser level.
published their paper on the possibility of laser
action in the infrared and visible spectrum it wasn't long before many
researchers began seriously considering practical devices.
Most experts were speculating that gases would be the first to lase in the
optical and infrared. It came as surprise that ruby was the first substance
to produce laser action in the visible spectrum (Maiman, 1960).
There was a bitter legal battle over who invented the laser (see
Initially it was thought that broadband optical pumping would be inefficient
but this was only for ions with very narrow resonances such as those in gases
and plasmas. When ions are embedded in a solid, they can absorb radiation in a
much wider band of wavelengths. Optical radiation of about 550 nanometers is absorbed
by dilute population of Cr+3 ions lightly doped in a corundum crystal matrix
(0.05% by weight Cr2O3 versus Al2O3 ) then a rapid non-thermal transition is made to a
lower metastable level whose lifetime is 5 milliseconds.
If the pump power exceeds a certain threshold, a population inversion can build
up between the ground state and this metastable state. The laser's performance
is greatly improved by enclosing it in an
The first successfully optical laser constructed by
(1960), consisted of
a ruby crystal surrounded by a helicoidal flash tube enclosed within a polished
aluminum cylindrical cavity cooled by forced air.
The ruby cylinder forms a Fabry-Perot cavity by optically polishing the ends to be
parallel to within a third of a wavelength of light. Each end was coated with
evaporated silver, one end was made less reflective to allow some radiation to
escape as a beam.
Photo-pumped by a fast discharge flash-lamp, the first ruby lasers operated
in pulsed mode for reasons of heat dissipation and the need for high pumping
powers. Nelson and Boyle (1962) constructed a continuous lasing ruby by
replacing the flash lamp with an arclamp.
A short while after the initial announcement of the first successful optical
laser, other labs around the world jumped on the bandwagon trying out
many different substrates and ions such as rare earths like
Nd, Pr, Tm, Ho, Er, Yb, Gd
even Uranium was successfully lased !
Many different substrates were tried such as
Yttrium Aluminum Garnet (YAG), glass (which was easier to manufacture), CaF2.
As manufacturing techniques improved these lasers rapidly made the transition
from the lab bench to commercial applications.
Dr. T H Maiman
with the first ruby laser
Initially, the laser was called an invention looking for a job.
- Harry Stine.
- Maiman,T.H.: 1960, Nature, 187, 493.
- Nelson,D.F., Boyle,W.S.: 1962, Appl.Opt. 1, 181.
- Schawlow and Townes : ...