Patent ID: 8064151
Filing Date: 2011-11-22
Classification: G03F,Y10S

Abstract:
1. A method, comprising: stabilizing a nominal temperature of a thermal optical element with a feedback loop to control heating of a plurality of heater elements; providing a desired temperature profile of the thermal optical element with a set point signal; determining a feed forward control of the heater elements from the set point signal; forwardly feeding an output of the feed forward control into the feedback loop; measuring, with a plurality of temperature sensors, a respective temperature at respective locations of the thermal optical element to determine a resulting measured temperature profile; computationally carrying out a modal decoupling of the measured temperature distribution to express said temperature distribution as a weighted sum over fundamental modes of the thermal optical element, said modes being called geometrical temperature profiles; determining, for each of the geometrical temperature profiles in the weighted sum, a corresponding driving profile parameter, which is a predicted distribution of power to be sent to the heating elements to maintain a given steady state geometric temperature profile; determining a feedback signal by forming a weighted sum of the individual driving profile parameters corresponding to each of the geometric temperature profiles, with each term in the sum being multiplied by the corresponding coefficient in the modal decoupling of the measured temperature distribution; and adjusting the feed-forward signal to reduce any difference between the feed-forward and feedback signals, such that the resulting measured temperature distribution is substantially equal to the desired temperature distribution.