LiF (200) crystals were heated with the x rays produced when a 30 J, 0.35 &mgr;m laser pulse of 0.6 ns duration was incident on a gold‐coated titanium target at an irradiance of 2.5×1015W cm−2. A filter arrangement allowed half of the crystal to be heated by the broad band x radiation from the gold plasma, whilst effectively shielding the other half of the crystal. The reflectivity of both x‐ray heated and unheated portions of the crystal was monitored by diffracting He‐&agr; radiation from the underlying titanium from both parts of the crystal. Significant increases in the integrated reflectivity (36%) of the heated crystal were found.