Refractive index of amorphous carbon near its K-edge

The refractive index of the amorphous carbon layers inside multilayer soft x-ray mirrors is derived in the λ = 42-58-Å wavelength range by measuring the shift in the Bragg angle caused by refraction. Reflectivity curves are measured with a reflectometer behind a zone plate monochromator at the National Synchrotron Light Source. The monochromator consists only of a freestanding zone plate of gold and an exit slit and is free of any of the contamination problems often found in monochromators that contain mirrors. © 1990 Optical Society of America.