Пишут про первый "настоящий" Х-лазер. Луч монохроматичный и когерентный. Хотя цифры и скромные, но для анализа материалов годится.
Physics - The Purest X-Ray Beam
To demonstrate that the LCLS is indeed coherent, a research team led by Ivan Vartanyants, of Germany's DESY synchrotron lab in Hamburg and the National Research Nuclear University in Moscow, used a form of the classic double-slit experiment
. They shined the laser pulses through a pair of pinhole apertures and observed the usual pattern of bright and dark bands produced by coherent light. The x rays vaporize most samples, so for pinholes, the team used a silicon sheet containing hundreds of "single-use" pinhole pairs with different spacings and focused the beam onto a new pair after each beam pulse.
The team observed very high contrast between the brightest and darkest regions of the pattern — high "visibility" — for small aperture separations. As the aperture spacing increased, the pattern received contributions from more widely separated photons in the beam, and without perfect coherence, the visibility decreased. By measuring this decrease, the team found the coherence length
— the distance over which the photons stay coherent. Their result was 16.8 microns, comparable to the width of the beam.
The researchers also measured the degree to which the beam is monochromatic
, which is equivalent to the coherence time. For large pinhole separations, they examined the visibility at the edge of the pattern, where the light travel distance from the two pinholes has the maximum difference, and any wavelength discrepancies would show up most clearly. They measured a coherence time of 0.55 femtoseconds, which means that the pulse was effectively the same color and intensity for that long, equivalent to a distance of about 150 nanometers along the beam direction
. So a 150-nanometer-deep sample can be illuminated with coherent light all at once.