Intended institutions and users:
Physics education in Medicine
How it works ...
The use of short-pulse lasers enables the generation of high peak power pulses in a short time, which are useful for the investigation of non-linear effects and for the investigation of time dependant effects e.g. time resolved spectroscopy. In order to achieve extremely high peak power up to the giga watt range, laser systems are applied, which possess long lived excited states able to store energy and to emit it in an extremely short time. One of such lasers is e.g. the Nd:YAG laser. With Q-switching in so called active or passive mode, it is possible to generate such short pulses. Here, in a first step the theory of laser operation with Nd:YAG is discussed and the steady state as well as time dependent solution of the four level rate equation is analysed. A two level rate equation model is introduced to explain the saturation behaviour of an optical absorber.
In the experiment first of all a mechanical chopper will be used to demonstrate the way towards active q-switch. In the second step a saturable absorber for passive q-switching is introduced. The dynamics of the pulse generation, like repetition rate, pulse width and peak power are determined.
The experiment consists of the laser diode pumped Nd:YAG - laser as basic version with an additional passive q-switch (Cr:YAG) crystal. 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 threshold, slope efficiency and so on.
By using the optional Pockels cell including the high voltage driver active Q-switch can be performed and explored.