X-RAY SUPERRADIANCE FROM MULTIPHOTON EXCITED CLUSTERS

Individual multiphoton excited clusters can exhibit superradiance in the 1-10 keV spectral region. This process may (1) confer a high level of coherence on the emission of an x-ray amplifier, (2) provide control of the emitted wavelength, and (3) produce x-ray pulses having durations less than or similar to 10 fs. For a transition having a lifetime determined by radiative decay, the lower bound on the wavelength of the superradiance for a cluster of n atoms having an interparticle spacing of r(0) is lambda(xr) similar to 2.9r(0)n(-1/6). For a system having a lifetime governed by Auger decay, the corresponding upper bound on the wavelength is lambda(xr) = (2 pi)(2)n(1/3)(mu(2) tau(a)/r(0)(2)h), with CL representing the transition dipole matrix element and tau(a)(-1) denoting the Auger decay rate.