Image Number 15 for United States Patent #7436423.
An apparatus and method for making a grayscale photo mask and a three-dimensional grayscale diffractive optical element operate as follows. A grayscale photo mask is obtained by exposing a laser direct write (LDW) glass material to laser beam radiation from a first laser beam of modulated power moved over a grid of discrete locations on the LDW material, the modulated power being in accordance with grayscale pattern data, and, while the first laser beam is moved over the discrete locations of the grid, exposing the grid to a second laser beam, the power of the second laser beam being less than the bleach threshold of the glass material, to provide each of the discrete locations with a gray scale level to provide a predetermined gray scale pattern of varying optical transmissivity on the LDW material to produce a grayscale mask. An optical element is obtained by exposing a photoresist layer on a wafer to radiation transmitted through the grayscale mask; and removing material from the photoresist layer to provide a predetermined varying thickness of the photoresist layer as determined by the gray scale patterns on the grayscale mask to produce the three-dimensional grayscale diffractive optical element. The optical element may be a diffraction grating. The power of the second laser exposed on said discrete locations may be between about 50 mW and about 5 W, and the power of the first laser exposed on the discrete locations may be between about 20 mW and about 500 mW.