They range in size from tiny semiconductor devices no bigger than a grain of salt to high-power instruments as large as an average living room. Still, whether they provide the energy that ignites a fusion reaction in isotopes of hydrogen, scan bar codes on produce in a supermarket, or provide the light source for Lucent Technologies high-capacity telecommunications systems, they all operate according to the basic principles put forth by Schawlow and Townes over forty years ago. Neither man was planning on inventing a device that would revolutionize a number of industries, from communications to medicine. They had something more straightforward in mind, developing a device to help them study molecular structures. A laser is a device that creates and amplifies a narrow, intense beam of coherent light.
Atoms emit radiation.
Normally, they radiate their light in random directions at random times. Reflective surfaces at both ends of the cavity permit energy to reflect back and forth, building up in each passage. The laser has contributed to humanity as a powerful scientific tool for expanding human knowledge and in its many applications that help people directly. In the 40 years since Arthur L. Schawlow and Charles H. Townes published their technical paper on the principles of the laser in 1958, the device has been put to work in a vast range of applications and has assumed many forms.