Permanent photowritten optical gratings in irradiated silicate glasses

We show that permanent optical gratings can be photowritten into simple silicate glasses by exposure to interfering beams of an Ar-ion laser after the glass has been treated by x rays. Gratings with index modulations as large as Deltan = 10(-5) can be formed in less than a minute by exposure to write beams with intensities of the order of 50 W/cm(2).