The diode lasers used for our experiments are very sensitive to small variations of temperature. This can cause the laser to drift away from the frequency that is needed for the experiment. Especially in the summer, and at times when the air conditioning switches off, the lasers are very unstable. To overcome this instability of the laser we used two stabilization techniques. The first technique makes use of saturation spectroscopy (section 2.7.1), the second technique makes use of a beat signal of two lasers which differ only slightly in frequency (section 2.7.2).