Abstract: A projection exposure apparatus for transferring a pattern formed on a mask onto a photosensitive substrate by a scanning exposure method, includes a light source for generating a light beam having a predetermined spatial coherence, an illumination optical system for receiving the light beam from the light source and illuminating a local area on the mask with the light beam, and a device for synchronously moving the mask and the photosensitive substrate so as to transfer the pattern on the mask onto the photosensitive substrate. A direction, corresponding to a higher spatial coherence of the light beam, is made to coincide with the direction of relative scanning an illumination area and the mask in the illumination area.

Abstract: A laser optical apparatus permits the use of a laser beam having a spectrum characteristic which substantially overlaps with an absorption band of oxygen, with a simple construction. Oxygen in a lens barrel of an optical system or a sealed space between lens barrels is absorbed by a deoxidation agent. Accordingly, even if a laser beam by an excimer laser using argon fluoride having a spectrum characteristic which substantially overlaps with the absorption of oxygen is passed through the optical system, the loss of laser energy by the absorption of oxygen, the generation of noxious gas and the swing due to the change of transmission are prevented.