2010 is the 50^th anniversary of the laser, a device which has significantly changed our lives gaining more and more importance with several and different types of applications.

In 1917 Albert Einstein described in one of his publications the process of stimulated emission of radiation. He could not know it, but that work laid the foundation for the laser which came after many years. Einstein discovered that a photon hitting an atom (or a ion or a molecule) not only supplies energy to this atom, but also causes the atom to release a second photon which moves in the same direction and with the same frequency as the first one. The last sentence has a great importance, since this phenomenon can be used to perform light amplification: we get two photons out of one thus transforming a light beam into another one with more energy. Although Einstein put the physical basis of the laser (the stimulated emission process), he can not be considered as the real inventor of this device. In 1959, the physicist Gordon Gould used for the first time the term "light amplification by stimulated emission of radiation" at a conference, and only a year later, the first working optical laser became a reality. More exactly, on May 16^th, 1960, physicist Dr. Theodore Maiman gave a demonstration of the first laser at the Hughes Research Laboratories. It was a ruby crystal rod with mirrored ends, collocated at the center of a coiled quartz flash tube. The tube lamp was able to provide a sharp white light, which energized chromium atoms in the ruby. The atoms, loosing energy, released photons which, bouncing on the mirrors, stimulated other atoms until they finally could escape out of one end of the rod in short pulses of red light. The following picture shows one of the first working laser, based on pink ruby cristal, used by Theodore Mainan:

Today the laser is used in medical applications (accurate surgical procedures), in the industry (used to cut and shape several types of materials), and for scientific tests and measurements. We use some laser application almost every day: to read and burn CDs and DVDs, to print our documents on a laser printer, to read a product's barcode when we buy something at a store, to improve our vision, in the security field, to keep track of time with high accuracy. A laser was even used to calculate the distance between the Earth and the moon: it was shot towards the moon and then, measuring the time took by the bounced beam to come back to the Earth, the moon’s distance was calculated.

The world’s biggest laser is located at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. It consists of 192 laser beams that focuses nearly two million joules of energy and create temperatures and pressures that exist in the cores of stars and giant planets. NIF has been constructed to ensure the safety and reliability of the nation’s nuclear deterrent without the need for nuclear testing. Moreover, offering the possibility to create the conditions that exist in supernovas, and in the cores of big planets, NIF will help to better investigate the secrets of the cosmos. The third and last application of NIF is, at least we all hope so, to provide a new source of clean energy for the 21^st century. The following picture shows a crystal artificially built in two months for NIF (it is a potassium dihydrogen phosphate crystal, also known as KDP):

An important characteristic of lasers is that they can be designed to run continuously with a precise well-defined frequency and wavelength, and they are able to achieve accuracy better than one part in 10¹⁶. This aspect enables laser light to provide a standard for time and length scales. The light beam produced by lasers has also a low divergence, and this property was actually used to reflect the beam from the mirrors placed on the moon by Apollo 11 and measure the distance of the moon itself from the Earth.

LaserFest

LaserFest has the purpose to celebrate the 50^th anniversary of the laser, which was first demonstrated in 1960 by Theodore Maiman, and will last for one entire year. LaserFest is a collaboration between the American Physical Society, the Optical Society, SPIE and IEEE Photonics Society. On the LaserFest website (here) there are many interesting resources related to the laser, as well as a detailed description and schedule of the events organized all over the world to celebrate the laser’s anniversary. The following image depicts the LaserFest’s logo:

Among the several resources available on the LaserFest site, there are also some interesting videos, like these:

• a video showing how lasers have transformed our lives in the last fifty years: http://www.laserfest.org/lasers/video-life.cfm
• a TV clip with Theodore Maiman who gives an explanation of the first ruby laser: http://www.laserfest.org/lasers/video-maiman.cfm