Microlight: lasing with single atoms.The process of generating a laser beam typically involves great crowds of atoms or molecules. Now, researchers have developed a microlaser that produces light from interactions between a mirrored cavity and atoms passing through that cavity one at a time. Kyungwon An, Michael S. Feld, and their coworkers at the Massachusetts Institute of Technology Massachusetts Institute of Technology, at Cambridge; coeducational; chartered 1861, opened 1865 in Boston, moved 1916. It has long been recognized as an outstanding technological institute and its Sloan School of Management has notable programs in business, report their results in the Dec. 19 PHYSICAL REVIEW LETTERS Physical Review Letters is one of the most prestigious journals in physics.[1] Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. . In a conventional laser, an electrical jolt or a flash of light excites atoms or molecules of a lasing material, such as a ruby crystal or a mixture of helium helium (hē`lēəm), gaseous chemical element; symbol He; at. no. 2; at. wt. 4.0026; m.p. below −272°C; at 26 atmospheres pressure; b.p. −268.934°C; at 1 atmosphere pressure; density 0. and neon gas. The photons emitted by excited atoms bounce back and forth between two mirrors, inducing additional atoms to emit light of the same wavelength. These photons move in step to create a coherent light co`her´ent light n. 1. (Physics, Optics) Light in which the phases of all electromagnetic waves at each point on a line normal to the direction of the the beam are identical. beam. To construct a microlaser, the researchers had to create a mirrored cavity, or resonator resonator /res·o·na·tor/ (rez´o-na?ter) 1. an instrument used to intensify sounds. 2. an electric circuit in which oscillations of a certain frequency are set up by oscillations of the same frequency in another , of sufficiently high quality to strictly limit the number of photons that could escape. They did this by fabricating a pair of precisely aligned, highly reflective mirrors for the project. The resulting resonator was about 10,000 times more capable of storing photons than a resonator in an ordinary laser. A "pump" laser was used to excite barium barium (bâr`ēəm) [Gr.,=heavy], metallic chemical element; symbol Ba; at. no. 56; at. wt. 137.33; m.p. 725°C;; b.p. 1,640°C;; sp. gr. 3.5 at 20°C;; valence +2. atoms from their ground state to a higher energy level just before the atoms entered the 1-millimeter gap between the two curved mirrors A curved mirror is a mirror with a curved reflective surface, which may be either convex (bulging outward) or concave (bulging inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. (see diagram). Interactions between the empty cavity and the first atom entering the gap induce the atom to emit a photon. The next excited atom traversing the cavity interacts with this photon, emitting a photon of its own, and so on. [CHART OMITTED] The number of photons present in the cavity quickly builds to a certain value, and a portion of the light can then emerge as a laser beam. Storing about 11 photons at a time in their resonator, the researchers generated a detectable laser beam having a wavelength of 791 nanometers. Such a microlaser may prove a useful tool for investigating how photons couple with individual particles. "This development has been long sought, and it is expected to lead to further fundamental advances in our knowledge of light and its interaction with atoms," Feld says. |
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