An international group of scientists has found that controlling the shape of laser pulses improves soft x-ray generation by nearly an order of magnitude. The technique incorporates a feedback loop to control the shape of the 800-nm pulses from a Ti:sapphire laser with a deformable silver-coated silicon nitride membrane.

The setup, which the team described in the July 13 issue of Nature, monitors the spectrum of the x-rays that are produced when the laser pulses interact with argon gas in a 175-µm-diameter, 3-cm-long tube. An evolutionary search algorithm controls the deformation of a membrane that shapes the laser pulses before they enter the tube. By adjusting the membrane to optimize the output at the laser's 27th harmonic and minimize the output at the neighboring harmonics, the system increased x-ray generation by a factor of eight.