There is a detached type of substances which is called semiconductors. In the first time that unique class was discovered in the 1890's but more completely it started to be discovered just after the First World War in Europe and in Soviet Union. In 1923 Russian scientists proved the ability of utilizing of semiconductor-metal contacts to quicken the generation of fluctuations. There was no opportunity to create some sophisticated devices as diodes. Only in the beginning of the 60's with the appearing of transistors in 1949 the wide usage of crystal detectors started. That was the beginning of the era of semiconductor technologies.
Stimulated emission is really a very interesting characteristic of semiconductors that has been discovered for several tens of years. By usage of such principles as p - n barriers and heterojunction scientists managed to create laser system in the beginning of the 60's.