THE FIRST PRACTICAL, COHERENT SOFT X RAY SOURCE has been devised by scientists at the University of Michigan. They convert laser light at a wavelength of 800 nm into light at x-ray wavelengths of 17-32 nm by sending it through a channel of gas. Until now the task of producing x rays by the "harmonic conversion" process has been hampered by the fact that the nonlinear crystals used to double the light frequency in the visible and ultraviolet soak up x rays, while the gas media more hospitable to x rays cause the x-ray beam to fall out of phase with the laser- light beam as they co-propagate through the conversion medium. The Michigan researchers succeed in preserving the phase match with the additional use of a fiber waveguide, thereby increasing the x-ray yield by a factor of 100 to 1000 over previous devices. (Rundquist et al., Science, 29 May 1998.)