Coherent-light emission from exciton condensates in semiconductor quantum wells

We show that a quasi-two dimensional condensate of optically active excitons emits coherent light even in the absence of population inversion. This allows an unambiguous and clear experimental detection of the condensed phase. We prove that, due to the exciton–photon coupling, quantum and thermal fluctuations do not destroy condensation at finite temperature. Suitable conditions to achieve condensation are temperatures of a few K for typical exciton densities and the use of a pulsed and preferably circularly polarized, laser.

Exciton beats in GaAs quantum wells: bosonic representation and collective effects

We discuss light–heavy hole beats observed in transient optical experiments in GaAs quantum wells in terms of a free-boson coherent state model. This approach is compared with descriptions based on few-level representations. Results lead to an interpretation of the beats as due to classical electromagnetic interference. The boson picture correctly describes photon excitation of extended states and accounts for experiments involving coherent control of the exciton density and Rayleigh scattering beating.

The Year-book of agriculture, or, The annual of agricultural progress and discovery / [edited] by David A. Wells.

1855-1856

Martinsburg, West Virginia and vicinity, ca. 1864 (Raster Image)

This layer is a georeferenced raster image of the historic paper manuscript map entitled: Plan of Martinsburg and vicinity. "This map was drawn by that noble officer Capt. C.L. Chandler and was much prized by our late Col. Geo. D. Wells, Chas. H. Howland, 1st Lt. & B. Gen., 34th Mass. Inf."-verso. It was sketched ca. 1864. Scale [ca. 1:9,250]. The image inside the map neatline is georeferenced to the surface of the earth and fit to the West Virginia State Plane North Coordinate System (in Meters) (Fipszone 4701). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, or other information associated with the principal map. This map shows features such as roads, railroads, selected dwellings with names of inhabitants, lines of pickets, troop location and camps, drainage, and more. Relief shown by form lines. This layer is part of a selection of digitally scanned and georeferenced historic maps of the Civil War from the Harvard Map Collection. Many items from this selection are from a collection of maps deposited by the Military Order of the Loyal Legion of the United States Commandery of the State of Massachusetts (MOLLUS) in the Harvard Map Collection in 1938. These maps typically portray both natural and manmade features, in particular showing places of military importance. The selection represents a range of regions, originators, ground condition dates, scales, and purposes.

Connecticut, Massachusetts, and Rhode Island, 1837 (Raster Image)

This layer is a georeferenced raster image of the historic paper map entitled: Map of Massachusetts, Rhode-Island & Connecticut : compiled from the latest authorities, engraved by J. Wells. It was published by A.F. Wilcox & Co. in 1837. Scale [ca. 1:442,000].The image inside the map neatline is georeferenced to the surface of the earth and fit to the USA Contiguous Albers Equal Area Conic projection (Meters). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This map shows features such as cities and towns, roads, railroads, drainage, churches, academies, banks, court houses, industry locations (e.g. mills, factories, mines, etc.), town, county, and state boundaries, and more. It also includes many inset maps of the major cities of New England.This layer is part of a selection of digitally scanned and georeferenced historic maps of New England from the Harvard Map Collection. These maps typically portray both natural and manmade features. The selection represents a range of regions, originators, ground condition dates, scales, and map purposes.

Nile River & Red Sea Region, ca. 1870 (Raster Image)

This layer is a georeferenced raster image of the historic paper map entitled: Egypt, Arabia Petraea, and lower Nubia, by Keith Johnston. It was published by William Blackwood & Sons ; W. & K. Johnston, ca. 1870. Scale [ca. 1:2,854,868]. Covers the Nile River and Red Sea regions.The image inside the map neatline is georeferenced to the surface of the earth and fit to the Egypt Red Belt projected coordinate system. All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This map shows features such as drainage, cities and other human settlements, territorial boundaries, shoreline features, roads, railroads, canals, wells, and more. Covers the Nile River and Red Sea regions.This layer is part of a selection of digitally scanned and georeferenced historic maps from the Harvard Map Collection. These maps typically portray both natural and manmade features. The selection represents a range of originators, ground condition dates, scales, and map purposes.