We report on frequency multiplication of microwave radiation by propagating space-charge domains in a semiconductor superlattice; the domains were due to a negative differential mobility of miniband electrons. We irradiated an arrangement of two GaAs/AlAs superlattices, mounted in a rectangular waveguide system, with microwave radiation (frequency near 70 GHz) and observed the generation of harmonics; the conversion of radiation power to the third harmonic showed a remarkable efficiency (5%). A theoretical study, based on a drift-diffusion model for the miniband electrons, suggests that the microwave radiation has driven the formation and annihilation of space-charge domains and that the resulting anharmonic current was the source of the frequency-multiplied radiation. Our results indicate that frequency multiplication by space-charge domains in a semiconductor superlattice can be exploited for efficient generation of submillimeter-wave radiation.
Britain's renegotiation of EC membership in 1974-5 has commonly been praised by historians as a tactical masterpiece by Prime Minister Harold Wilson in holding a divided country and party together while also keeping Britain inside the European Community. By contrast, this article focuses on the detrimental effect the episode had on Britain's standing inside the EC. Using the prism of high-level diplomacy between Wilson and the German Chancellor Helmut Schmidt, it reconstructs precisely the changes in German perceptions of British positions, showing how initial goodwill towards Britain's demands soon gave way to widespread scepticism over British motives and ultimate intentions. While highlighting the strong domestic pressures driving Britain and Germany apart, the article ultimately argues that these differences were unnecessarily exacerbated by Wilson's failure at personal diplomacy on the highest level. A different handling of Schmidt may not have resulted in a radically different outcome of the renegotiations; but it may well have avoided the profound sense of distrust and suspicion over Britain's future role in Europe that the episode stimulated among the Germans. The article is based on recently declassified sources from three countries, as well as on rare materials from Schmidt's private archive in Hamburg.
The almost thirty years between the end of the Second World War in 1945 and Helmut Schmidt's election as West German chancellor in 1974 saw profound shifts in the relative power balance between Britain and Germany. In 1945, Britain was a victorious power with still global reach; its dominions and colonial possessions stretched across Africa, Asia and Australia, and it still counted over 700 million people as citizens of the British Empire and Commonwealth. 1 The scope of Britain's geostrategic reach was matched by its financial and economic dominance: in 1950, Britain produced almost one-third of Western Europe's industrial output, and half of the world's trade was conducted in pounds sterling. 2 Germany, by contrast, was a comprehensively defeated, divided and occupied country, shouldering the unique historical burden of the Holocaust and the Second World War. 3 Less than thirty years later, however, the situation looked very different indeed. By 1970, the FRG had become Western Europe's undisputed economic powerhouse, with its share of world exports of manufactures amounting to almost 20 per cent. 4 The FRG's economic power had also become increasingly reflected in the political realm, with the country taking on prominent roles inside the multilateral alliances of the EC and NATO. Britain, by contrast, was suffering from a profound loss of military, political and economic strength caused by its transition to a medium-sized post-imperial power. By the mid 1960s, Britain's share
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