Bright source of K [alpha] and continuum X rays by heating Kr clusters using a femtosecond laser

X rays emitted from Kr clusters illuminated by a femtosecond laser have been observed over a wide spectral region from 3 keV to 15 keV. The measured spectra are characterized by a broad bremsstrahlung continuum and K[alpha], [beta] lines at 12.66 keV and 14.1 keV. To the best of the authors' knowledge, this is the first observation of K[alpha], [beta] emission from laser-heated Kr clusters. The bremsstrahlung continuum arising from collisions in the plasma implies a population of hot electrons consistent with a temperature of several kiloelectron volts. The absolute X-ray yield in the 3-15 keV region is found to be of the order of 107 photons per laser pulse. The plasma temperature, estimated from the continuum part of the spectrum as a function of laser intensity and X-ray yield as a function of laser pulse duration, are studied.