Patent ID: 7675663

Claim:
An apparatus for producing a hologram mask provided with an interference fringe having modulation information relative to a light transmittance and a phase by using a plurality of original masks, comprising: a light source; an optical system of an object light, wherein a light from the light source enters a hologram material as the object light through one of the original masks having a light transmitting-screening pattern; an optical system of a reference light, wherein a light from the light source enters the hologram material as the reference light not through the original masks; a phase modulator causing a phase difference between the object light and the reference light by changing an optical path length and provided on at least either the optical system of the object light or the optical system of the reference light, wherein the phase modulator causes a first phase difference between a first object light and a first reference light in a first exposure and a second phase difference between a second object light and a second reference light in a second exposure following the first exposure; wherein the modulation information of the interference fringe that accrues by the first object light through the first original mask and the first reference light interfering with each other at the first phase difference in the first exposure is recorded on the hologram mask, and the modulation information of the interference fringe that accrues by the second object light through the second original mask and the second reference light interfering with each other at the second phase difference in the second exposure is recorded on the hologram mask; and further comprising means for reducing the light intensity ratio of an object light to a reference light so as to be smaller than a light intensity ratio necessary for maximizing a diffraction efficiency value due to the interference fringe to be formed in the hologram mask.