Optical pumping in conjunction with Nd:YAG lasers is of particular interest, because these have become widely accepted for industrial use, along with the CO2 laser. The laser-active material which, in the case of the Nd:YAG laser, is excited by optical pumping, consists of Neodymium atoms that are accommodated in a transparent YAG host crystal (Yttrium Aluminium Garnet).
Whereas up to a few years ago Nd:YAG lasers were always excited using discharge lamps, optical pumping with laser diodes is becoming more and more significant. This is because laser diodes are available economically and they emit narrow band light at high optical powers, which matches the energy levels of the Nd:YAG crystal. The advantage over the discharge lamp is that the emission of laser diodes is nearly completely absorbed by the Nd:YAG, whereas the very wide spectral emission of discharge lamps is absorbed to only a small extent only.
The four level system is explained, a theoretical analysis of the Nd:YAG laser is performed, and a rate equation model derived. The steady state solution is presented, and the dynamic situation considered to investigate spiking.
The kit contains all components necessary to assemble a diode pumped Nd:YAG laser - a 1 W diode with driver and Peltier controller, collimating and focusing optics, Nd:YAG crystal, laser mirrors, a photodiode detector and all necessary mounts etc.
The stability criterion of the resonator are verified experimentally. The dependence of the pump wavelength on diode temperature and drive current are proven, and the absorption spectrum of Nd:YAG derived. By using a few additional modules, this basic set-up can be up-graded to LE-0700 „Frequency Doubling with KTP“ or LE-0800 „Generation of short pulses“. Furthermore the components for the oscillation at 1.3 µm including frequency doubling to "red" or an active or passive Q-switch are available as options.
Laser operation of Neodymium was first demonstrated by J. E. Geusic et al. at Bell Laboratories in 1964. In the same way as for Chromium atoms of the ruby laser the Neodymium atoms are embedded in a host crystal which in this case is a composition of Yttrium, Aluminium and Oxygen (Y3Al5O12) forming a clear crystal of the structure of a garnet. The Neodymium is replacing a small fraction of the Yttrium atoms and due to the integration inside the lattice it is triply ionized (Nd3+). The outstanding property of such a Nd:YAG laser lies in the fact that the laser process takes place inside a 4 level energy system as shown on the left. This and the possibility of creating more than 10.000 W output power made this laser to an indispensable tool for a great variety of applications. Furthermore this laser system is an integral part of the lectures in photonics since it exhibits the important level laser system. In this system the population inversion is created between the energy levels (3) and (4) and since (2) is far above the ground state its population is zero. So even a single excited Neodymium ion provides an population inversion.
For the excitation of the Neodymium ions a laser diode (LD) is used which emits laser radiation at a wavelength of 808 nm. A collimator transforms the emission in an almost parallel light bundle which is focussed by the lens (FL) into the Nd:YAG rod. The optically cavity is formed by the mirror M1 and M2 whereby the plane mirror M1 is coated to ones side of the Nd:YAG rod and the spherical mirror M2 has a radius of 100 mm.