Lithographic apparatus and device manufacturing method

A method of correcting a projected image measurement within a lithographic apparatus comprising:

• projecting a patterned radiation beam using a projection optical system;
• measuring a wavelength variation of the radiation beam;
• measuring image information of the patterned beam;
• and
• correcting the measured image information based on the measured wavelength variation.

A lithographic projection apparatus comprising:

• an illumination system configured to condition a radiation beam;
• a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
• a substrate table constructed to hold a substrate;
• a projection system configured to project the patterned radiation beam onto a target portion of the substrate;
• a sensor, constructed and arranged to measure a wavelength variation of the radiation beam;
• and
• a controller, configured and arranged to adjust a focal plane of the lithographic projection apparatus based at least in part on wavelength variation measurements of the sensor.