INCREASE OF MULTILAYER X-RAY REFLECTIVITY INDUCED BY PULSED-LASER HEATING

The reflectivity of tungsten-carbon (W-C) multilayers, heated by 7 ns Nd-YAG laser pulses was measured using soft x-ray radiation at 4.4 nm. The reflectivity permanently increased and the Bragg angle decreased after heating the multilayer at fluences of 03 j/CM2 . The reflectivit y increase was achieved in a narrow domain of heating fluences. A quan titative model based on laser absorption and heat transport, that expl ains the melting phenomenon of tungsten and the heating to a temperatu re where graphitization is possible in the carbon layers, is presented . The two phenomena: (a) increase in x-ray reflectivity and (b) expans ion of the multilayer mirror can be explained by the laser heating. Th e improvement of reflectivity is caused by the smoothening of the tung sten layers due to melting, while the change in the spacing is attribu ted to the carbon phase transition (graphitization).