Basic Concept

Within this experiment, the first step discusses the theory of laser operation with Nd:YAG and the steady state as well as the time dependent solution of the four level rate equation. A two level rate equation model is introduced to explain the saturation behaviour of an optical absorber applied as passive q-switch.
In the second step, a saturable absorber for passive q-switching is introduced. The dynamics of the pulse generation, like the repetition rate, pulse width and peak power are determined. In the final step, Pockel��s cell as an active q-switch is applied.
The experiment consists of the laser diode pumped Nd:YAG laser, with an additional passive (Cr:YAG) and active Q-switch (Pockels��s cell).
The time dependant signals are displayed and evaluated using an optional oscilloscope. Beside the generation of short pulses, the behaviour of the Nd:YAG laser can also be the subject of additional investigations, like measuring the thres-hold, slope efficiency, etc.

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 analyser (OMA) or to the photodetector (PD). When the laser mirror is removed, the excitation spectra can be recorded by means of the OMA.
By inserting the active or passive q-switch inside cavity the laser starts to operate in pulsed mode. The subsequent mea-surements 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. Furthermore, the active and passive q-switching technique is demonstrated.