Divergence and intensity of amplified spontaneous emission coupled out of an active medium by a distributed refraction method

The dynamics of the radiation in the near and far zones has been studied analytically and numerically for the case in which nonlinearly amplified spontaneous x radiation is coupled out of a plasma active medium by a distributed refraction method. The divergence Δθ of the amplified noise falls off exponentially with increasing length of the active medium, z. When z is equal to five or six refraction lengths, Δθ is an order of magnitude smaller than the geometric divergence. The maximum radiation flux q_m is at the refraction angle and increases exponentially with increasing z. The rate of increase of q_m and the rate of decrease of Δθ may be lowered by diffraction. In the case of a linear amplification of the noise, q_m also corresponds to the refraction angle and may be much greater than the paraxial flux density. However, the advantage over coupling out the end in the case of a homogeneous active medium is achieved at a substantial cost in power.