Inversionless amplification of coherent THz radiation

An inversion-less amplification of coherent THz emission is achieved by coherent superposition with an electromagnetic background field. This process is applicable to a wide variety of optically impulsively excited THz emitters. The amplification is experimentally demonstrated both in single-pass as well as in resonator configurations. The fundamental limits and prerequisites are discussed, stressing analogies and differences to standard amplification by stimulated emission.