Laser-induced diffraction patterns in germanium diselenide amorphous films.
We report the characterization of changes produced on germanium diselenide amorphous semiconductor thin films by a focused He-Ne laser beam. The diffraction pattern produced by the laser spot on the sample is studied as a function of the intensity and the irradiation time. At low intensities the state of polarization of the incident beam generates an asymmetry in the induced diffraction pattern. Moreover, if the polarization of the incident beam is rotated, the corresponding asymmetry rotates as well. These results show the difference between thermal and electromagnetic effects on the material. This system may be used as a high density recording medium.
Phase conjugation and spatial grating formation in amorphous chalcogenide thin films
We present experimental results of phase conjugation (PC) via degenerate four-wave mixing in amorphous Se, Ge10Se90 and Te7Se93 semiconductor thin films. Simultaneously to the PC signal a laser induced grating is formed. However the relief of the grating alone does not seem to explain the experimental results. Measurements of the PC intensity as a function of the film thickness suggest that besides the surface relief, volume effects have to be considered. The PC intensity is measured as a function of the irradiation intensity. The induced gratings are characterized by atomic force microscopy.
Professor Penck's Bluff: Geography, Espionage and Hysteria in World War I
Abstract This article considers the image of geography during World War I through a discussion of newspaper controversies about the pre‐war activities of German and British geographers. Early in the war, Sven Hedin and Albrecht Penck, renowned geographers whose achievements had been widely celebrated by the British geographical establishment, were named in the media as enemy spies whose supposedly disinterested scientific inquiries in Britain and the Empire had masked their real intention to pass sensitive information to the German High Command. British geography stood accused of collusion with enemy ‘super spies’. This article examines how Britain's geographical community, represented by the Royal Geographical Society, sought to defend the discipline's patriotic virtue and head off a full‐scale media witch‐hunt. In so doing, the article comments on the media's role in shaping the image of geography and on geography's place in public debates about the sanctity of the national space.