Amplification of coherent THz radiation without inversion

Summary form only given. Attractive applications of coherent THz radiation from impulsively optically excited emitters have been demonstrated. Their widespread utilization however is limited by the lack of powerful and efficient sources. One of the main limiting effects is the destruction of the coherence in the emitter system by ultrafast dephasing processes. These restrict the coherent emission time /spl tau//sub coh/ to a fraction of the radiative lifetime, so that only a small portion of the available energy is emitted coherently which results in a low efficiency. A drastic enhancement can be obtained by increasing the emission power in order to emit more energy coherently before dephasing occurs. Here we present a new inversionless technique to amplify the emission power of a THz emitter by a phasematched superposition with a coherent THz background field during the emission process.