Projection exposure apparatus and device manufacturing method

A projection exposure apparatus comprising:

• illumination means for illuminating a mask with laser light from a laser;
• a projection optical system for projecting a pattern of the mask as illuminated with the laser light, said projection optical system including a plurality of refractive optical elements made of at least two materials, wherein interspaces of the refractive optical elements are filled with at least two different types of gaseous fluids, while a pressure of each gaseous fluid is kept the same as or substantially the same as the atmospheric pressure, the at least two different types of gaseous fluids filling different interspaces, respectively, wherein the gaseous fluids are a helium gas and a nitrogen gas;
• detecting means for detecting a change in atmospheric pressure and for producing an output;
• and
• changing means for changing a wavelength of the laser light on the basis of the output of said detecting means, wherein, by changing the wavelength of the laser light with said changing means, a change in a predetermined optical characteristic of said projection optical system resulting from a change in the atmospheric pressure can be corrected or reduced.