Abstract: According to one aspect of the present invention, there is provided a photomask inspection apparatus which observes a pattern provided on a mask substrate of a mask to inspect the mask including an object lens, and a liquid that is present between a last lens in the side closer to the mask of the object lens and the mask.

Abstract: According to one aspect of the present invention, there is provided a photomask inspection apparatus which observes a pattern provided on a mask substrate of a mask to inspect the mask including an object lens, and a liquid that is present between a last lens in the side closer to the mask of the object lens and the mask.

Abstract: An interferometer of Mach-Zehnder type includes a first half mirror dividing an entrance light flux into first and second light fluxes, a first reflection mirror reflecting the first light flux toward a second half mirror, and a second reflection mirror reflecting the second light flux toward the second half mirror. At the second half mirror, the first and second light fluxes are mixed to derive an exit light flux including interference fringes. The first half mirror and first reflection mirror are secured to opposing side walls of a first hollow supporting block made of ceramics, and the second half mirror and second reflection mirror are secured to a second hollow supporting blocks made of ceramics. The first and second supporting blocks are coupled with each other at their side walls and an assembly of the supporting blocks is mounted on a surface of an optical bench by means of kinetic mounts.