Early History of the Laser
In 1917, Einstein laid the foundation for the laser when he introduced the concept of stimulated emission; where a photon interacts with an excited molecule or atom and causes the emission of a second photon having the same frequency, phase, polarization and direction. The acronym LASER stands for "Light Amplification by Stimulated Emission of Radiation".
The First Laser
Theodore Maiman developed the first working laser at Hughes Research Lab in 1960, and his paper describing the operation of the first laser was published in Nature three months later. Since then, more than 55,000 patents involving the laser have been granted in the United States. Today's laser and all of its applications are the result of not one individual's efforts, but the work of a number of prestigious scientists and engineers who were leaders in optics and photonics over the course of history. These include such great minds as Charles Townes at Columbia University, who developed the maser, the precursor to the laser, and Arthur Schawlow at Bell Laboratories, who along with Townes published a key theoretical paper in 1958 that helped lead to the lasers development and who jointly were awarded the first laser patent in 1960.
Maiman's early laser used a powerful energy source to excite atoms in a synthetic ruby to higher energy levels. At a specific energy level, some atoms emitted particles of light called photons. These newly created photons struck other atoms, rapidly stimulating the emission of more identical photons and amplifying the light intensity. Maiman was able to continue this process of stimulated emission and amplification by placing a completely reflecting silver mirror on one end of the model and a partially reflecting silver mirror on the other. This setup enabled photons to bounce back and forth between the mirrors until they gained enough intensity to burst through the partially silvered end as a powerful, coherent, beam of light--what you can today find on the end of a laser pointer.