Methods and systems are described herein for producing high radiance illumination light for use in semiconductor metrology based on a confined, sustained plasma. One or more plasma confining circuits introduce an electric field, a magnetic field, or a combination thereof to spatially confine a sustained plasma. The confinement of the sustained plasma decreases the size of the induced plasma resulting in increased radiance. In addition, plasma confinement may be utilized to shape the plasma to improve light collection and imaging onto the specimen. The induced fields may be static or dynamic. In some embodiments, additional energy is coupled into the confined, sustained plasma to further increase radiance. In some embodiments, the pump energy source employed to sustained the plasma is modulated in combination with the plasma confining circuit to reduce plasma emission noise.