Rubidium is a very reactive alcali metal of the first group of the table of elements. It was first discovered by Bunsen and Kirchhoff in 1861 using spectroscopic investigations. Due to its typical red color of the spectral lines it was named after the Latin word 'rubidus' (darkred). It is characterized by one valence electron. The natural abundance of Rubidium isotopes is ⁸⁵Rb(72.2%) and ⁸⁷Rb(27.8%).

There are several optical transitions at 780nm. Their electronic levels are shown in the excerpt of the level scheme. ⁸⁵Rb shows the transition indicated 2 and 3, while ⁸⁷Rb shows the transitions indicated by 1 and 4.

All four indicated optical transitions are observed during a Rb absoption experiment with our tunable external cavity diode lasers as shown on the above absorption spectra. The figure below shows the Lamb dips (and the cross-over lines) of transition 2, investigated with a typical saturation absorption experiment. 

These experiments have been performed with our TEC100 Littrow Laser System, as well as with our TEC300 Power Littrow Laser System and with our TEC500 Littman Laser System. We gratefully acknowledge finanical support by the BMBF within contract 13N7157. For more details, please check our publications.