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). Before, Nd:YAG lasers were mainly excited using powerful discharge lamps, optical pumping with laser diodes is becoming more and more important. Today powerful laser diodes are available at low cost 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 used 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.