PHY 452/562 Laser History In 1916, Albert Einstein predicted the existence of stimulated emission, based on statistical physics considerations. Einstein, A., “Zur Quantentheorie der Strahlung,” Physikalische Gesellschaft Zürich, 18, 47‐62 (1916). He never considered the possibility of amplification. PHY 452/562 Amplification of light through stimulated emission requires population inversion. In equilibrium, lower energy levels are always more populated. As a result, absorption always dominates. In order for the stimulated emission to become significant, higher energy levels should be artificially made There are many ways of more populated. This is called pumping, including population inversion. It is achieved electrical and optical. via «pumping». PHY 452/562 MASER Amplification of electromagnetic radiation via stimulated emission was first performed in the microwave region, by Charles Townes and Arthur Schawlow. Also by Nikolay Basov and Alexandr Prokhorov in the USSR. (Nobel prize 1964). Phys.Rev., 95 p‐282 (1954) Townes and Schawlow suggested that achieving optical masers could be solved by using feedback via an optical cavity. PHY 452/562 The term laser was first used by Gordon Gould in 1959. He also sketched the first laser resonator. The first working laser was built By Theodore Maiman at Hughes Research lab, in 1960. The laser was a solid state ruby laser, optically pumped. Nature,187 p‐493 (1960) PHY 452/562 This unique powerful and coherent light source received enormous attention for various applications. New uses of lasers emerge almost every day. Since the laser developments preceded the applications, the term “solution looking for a problem” is used for lasers. CO2 laser was invented in 1963 by K. Pattel. CO2 is the workhorse for laser metal cutting and welding. Phys. Rev., 136a, P‐1187 (1964) PHY 452/562 Fiber Lasers In 1964 C. J. Koester and E. Snitzer developed the first neodymium‐doped fiber amplification, paving the way for fiber telecommunications. Applied Optics, 3, 1182‐1186 (1964). PHY 452/562 The first barcode scanner was made in 1974. Ultrafast Laser Pulses Today it’s routine to generate ultrashort laser pulses with durations < 100 femtosecond (10‐13 s). The extreme high intensities yield many nonlinear‐optical effects. The first femtosecond laser was developed in 1974 by Ippen and Shank. Appl. Phys. Lett. 24, 373‐375 (1974) PHY 452/562 Laser Nobel Prizes 1964: Charles H. Townes, Alexander M. Prokhorov, and Nicolay G. Basov for the construction of oscillators and amplifiers based on the maser‐laser principle. 1966: Alfred Kastler for the discovery and development of optical methods for studying resonances in atoms. 1971: Dennis Gabor for his invention and development of the holographic method. 1981: Arthur Schawlow and Nicolaas Bloembergen for the development of laser spectroscopy. PHY 452/562 Laser Nobel Prizes 1997: Steven Chu, Claude Cohen‐Tannoudji and William D. Phillips for the development of methods to cool and trap atoms with laser light. 1999: Ahmed Zewail for his studies of the transition states of chemical reactions using femtosecond spectroscopy. 2000: Zhores I. Alferov and Herbert Kroemer for developing semiconductor heterostructures used in high‐speed‐ and opto‐ electronics. PHY 452/562 Laser Nobel Prizes 2001: Eric Cornell, Carl Wieman, Wolfgang Ketterle for the “achievement of Bose‐Einstein condensation in dilute gases of alkali atoms.“ 2005: Roy J. Glauber, John L. Hall, Theodor W. Hansch for their "contributions to the development of laser‐based precision spectroscopy, including the optical frequency comb technique". PHY 452/562 Laser Nobel Prizes 2009: Charles K. Kao, Willard S. Boyle, and George E. Smith for groundbreaking achievements concerning the transmission of light in fibers for optical communication". 2012: Serge Haroche and David Wineland for ground‐breaking experimental methods that enable measuring and manipulation of individual quantum systems..