ABSTRACT
Immediately after the publication of the paper by Arthur L Shawlow and Charles Hard Townes, and even before this, a number of people had begun to think about different strategies for the production of inverted populations in the infrared and visible regions. Of course the main themes were influenced by the ideas of these two researchers and most people were expecting the first laser action to take place in an excited gas. The success obtained by Theodore Harold Maiman with the ruby laser was truly a surprise. The laser is characterized by certain properties peculiar to the kind of source: coherence that is the ability to give interference phenomena; directionality and collimation; an emission on a very narrow band of frequencies with a very large power. Organic dye lasers allowed a long pursued dream to be realized: to obtain a laser that was easily tuneable over a wide range of frequencies.
