Basics

The creation of a population inversion within a semiconductor is the main part of the chapter €žbasics€œ. The comparison to €žclassical lasers€œ is made and the consequences with regard to the functioning of a diodelaser are pointed out. These are, for instance, the dependence of the emission wavelength on temperature and injection current as well as the spatial and spectral properties of the diodelaser radiation.
The laser diode is mounted in a rotational stage which allows the independent rotation around the beam propagation axis as well as perpendicular to this axis to measure the spatial distribution of the emitted laser light (A).
The set-up provides a set of cylindrical lenses to convert the elliptical beam profile into an almost circular one. In this case the vertical as well as parallel intensity distribution (A) become almost identical.
Another property of the emission of the diodelaser is its polarisation purity. For a higher injection current the ratio of the horizontal and perpendicular polarised intensity is in creasing. The polarisation for different values of the injection current is measured by means of a the provided polarisation analyser.
The maximum absorption is characterised by a significant reduction (B) of the diodelaser radiation at the exit of the Nd:YAG crystal. At this point the wavelength of the emission of the diodelaser has the same value as the well known absorption peak of the Nd:YAG material (804.4 nm). If the injection current and the temperature of the diodelaser are now modified in such a way that the maximum absorption is maintained, one gets the values shown in (C). From this, the dependence of the diodelaser€™s emission wavelength on temperature and injection current can be determined.