Semiconductor Diode Lasers in Atomic Spectroscopy

The use of lasers in experiments of atomic and molecular spectroscopy opened new possibilities to the investigation of these fundamental components of matter. The well known properties of intensity, spectral purity, and directionality of the laser radiation, gave rise to completely new techniques. Both sensitivity and spectral resolution improved by several orders of magnitude with respect to conventional spectroscopy. Of course, due to the central role played by the laser in such experiments, the scientific achievements strictly followed the technical development of the laser sources. Until recently, dye lasers dominated the scenery. They were the only lasers which could be tuned to any particular wavelength in a wide spectral range spanning from the ultraviolet to the near-infrared. However, dye lasers are very expensive and require a large pump laser (an Ar+ or Kr+ ion laser for cw dye lasers). This restricted the use of such lasers and made it virtually impossible to think of experiments in which more than one or at most two lasers were needed. In the experimental set-ups there was very often an evident unbalance between the size of the sample cell, usually a simple glass bulb or an electrical discharge, and the laser used to investigate it.