LIGHT INTENSITY CONTROLLER AND ITS CONTROL METHOD

摘要

PROBLEM TO BE SOLVED: To provide a light intensity controller and a light intensity control method thereof for exactly controlling the light quantity of principal light beam regardless of the change of the polarization dependent characteristic of a light splitting element depending upon humidity. SOLUTION: This controller is provided with a humidity dependent correcting means for detecting the changed amount of the polarization dependent characteristic of a light splitting element 11 depending upon humidity, feeding back the changed amount of the polarization dependent characteristic to a polarization correcting means and making the polarization correcting means A correct the output of a monitor light detecting means so that the output signal intensities of monitor light detecting means 13, 14 and the light intensity of the principal light beam on the objective surface have a constant correlation in spite of the change of humidity.