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Basic Concept
Optical pumping of Nd:YAG lasers is
of particular interest because they have become widely accepted
for industrial and medical use, along with the CO2 laser. The
laser active material which, in the case of the Nd:YAG laser,
consists of Neodymium ions accommodated in a transparent YAG
host crystal (Yttrium Aluminium Garnet). Where only up to few
years ago, Nd:YAG lasers were mainly excited using powerful
discharge lamps, optical pumping with laser diodes is becoming
more and more important. This is because powerful laser diodes
are nowadays available economically and they emit light at high
optical power levels with a narrow spectral bandwidth, which
matches perfectly with the energy levels of the Nd:YAG crystal.
The great advantage over the discharge lamp is that the emission
of the laser diodes are almost completely absorbed by the Nd:YAG,
whereas the relatively broad spectral emission of discharge
lamps is absorbed to only a small extent.
Experimental Set-up
The light of the pump laser is transferred via a fibre cable to
the fibre telescope (FT-1) which transforms the beam to an
almost parallel beam. The lens (C) focuses the radiation into
the Nd:YAG rod, which has a mirror coating on its back side and
forms the cavity with the laser mirror. The generated laser
emission at 1064 nm passes the filter (Fi) and the residual pump
light is blocked. The passed laser emission can be transferred
by means of the fibre telescope (FT-2) either to the optical
multi-channel analyzer (OMA) or to the photodetector.
When the laser mirror is removed, the excitation spectra can be
recorded by means of the OMA. By varying the temperature of the
laser diode its wavelength will change. This effect can be
studied first and then exploited to obtain the absorption
spectrum of the Nd:YAG crystal. By modulating the pump laser,
the time resolved emission spectrum allows the measurement of
life-time of the excited state. The measurements can be
performed either in local mode or through computer control via
the USB connection of the base housing.
This set-up is ideally suited to demonstrate the fundamental
behaviour of a solid state laser system, its excitation process
as well as its spectroscopic characteristics. |
