The invention of the laser in 1960 spurred new research in physics and unforeseen applications [1] . The first laser looks like a simple device, but its invention required the knowledge and skills of scientists and engineers who were familiar with theoretical models of semiconductor and solid state physics [2] and had worked on radar and transistor developments [3] .
More on how a laser works
Curiously, the laser found its first practical application (for barcode scanners) only in the mid-1970s, while from the beginning the invention instigated scientific and technological work in the burgeoning field of photonics, exploiting the interaction of photons and electrons (for the magic of light, see Atmospheric Optics and Canon Science Lab ).
The dated Bohr model is still often used for a simple explanation of atomic energy levels. The modern atomic model reveals a multitude of overlapping energy sublevels, leading to the band structure theory that describes electrical and optical properties of semiconductors and crystals (see also Transistor and related Note 1).
The laser was preceded by the maser, invented in 1953. The maser uses a resonating cavity to generate high-intensity microwaves, a technology first implemented in magnetrons that generated radar waves in World War II. To achieve amplification of light waves that are 100,000 times shorter and oscillate 100,000 times faster than microwaves, an optical resonator had to be invented.