CO2 laser stabilization systems and methods

Abstract

Systems and methods for stabilizing a CO 2 laser are disclosed. The system includes a detector unit for measuring the power in a select portion of the output beam. The detector unit generates an electrical signal corresponding to the measured power. The modulation frequency of the signal used to modulate the relatively high-frequency radio-frequency (RF) pump signal is filtered from the electrical signal. The filtered electrical signal is then-compared to a desired value for the output power in the output beam. Based on the comparison, a modulation control signal for modulating the RF pump signal is formed. The modulation control signal has a varying duty cycle that varies the amount of laser pump power to reduce or eliminate the measured variations in the output beam power. The result is an output beam power that remains stable over time.

1 - 4 . (canceled)  
   
   
       5 . A system for stabilizing an output laser beam from a CO 2  laser pumped by a modulated radio frequency (RF) signal, comprising: 
 a detector unit arranged to measure an output power of the output laser beam and generate a corresponding electrical signal;    a conditioning electronics unit operably coupled to the detector unit and adapted to remove the modulation frequency from the electrical signal to form a conditioned electrical signal; and    a pulse-width modulation (PWM) controller operably coupled to the conditioning electronics, the PWM controller adapted to receive the conditioned electrical signal and form therefrom a modulation control signal having a duty cycle that varies to reduce or eliminate measured variations in the output power.    
   
   
       6 . The system of  claim 5 , wherein the detector unit includes: 
 an integrating sphere having an acceptance aperture; and    a photodetector optically coupled to the integrating sphere.    
   
   
       7 . The system of  claim 6 , further including a mask adjacent the acceptance aperture, the mask having a mask aperture shaped and positioned to pass only a first portion of the output laser beam that is associated with producing a desired processing effect.  
   
   
       8 . The system of  claim 5 , wherein: 
 the PWM controller includes a field-programmable gate array (FPGA) programmed to:    receive the electrical signal in digital form;    compare an amount of power represented by the digital electrical signal to a desired power set-point value; and    form from said comparison the modulation control signal that limits the output power to an amount equal to or less than the power set-point value.    
   
   
       9 . The system of  claim 5 , wherein the PWM controller and the laser are operably coupled by an optical fiber, and wherein the modulation control signal is transmitted from the PWM controller to the laser as an optical signal.  
   
   
       10 . A laser thermal processing (LTP) system for processing a substrate having a surface, comprising: 
 a radio-frequency (RF)-pumped CO 2  laser;    the CO 2  laser stabilization system operably coupled to the CO 2  laser to stabilize an output laser beam from the CO 2  laser, including: 
 a detector unit arranged to measure an output power of the output laser beam and generate a corresponding electrical signal;  
 a conditioning electronics unit operably coupled to the detector unit and adapted to remove the modulation frequency from the electrical signal to form a conditioned electrical signal; and  
 a pulse-width modulation (PWM) controller operably coupled to the conditioning electronics, the PWM controller adapted to receive the conditioned electrical signal and form therefrom a modulation control signal having a duty cycle that varies to reduce or eliminate measured variations in the output power;  
   a beam-directing member arranged to direct a portion of the stabilized output laser beam to an optical system adapted to form an LTP beam, which in turn forms an image at the substrate surface, said image being capable of heating the substrate surface;    a chuck adapted to support the substrate; and    a stage adapted to movably support the chuck so as to move the substrate relative to the image to effectuate scanning of the image over the substrate to thermally process the substrate.    
   
   
       11 . A method for thermally processing a substrate, comprising the steps of: 
 a. generating a stabilized output laser beam from a CO 2  laser, wherein the stabilized output beam has an amount of power that varies over time by no more than 1% over a 24 hour period;    b. directing a portion of the output beam to an optical system adapted to form an LTP beam capable of heating the substrate; and    c. directing the LTP beam to the substrate to heat the substrate.    
   
   
       12 . The method of  claim 11 , further including the step of: 
 e. moving the substrate relative to the LTP beam so that an image formed by the LTP beam moves over the substrate.    
   
   
       13 . The method of  claim 12  further including the step of: 
 f. measuring only a portion of the output laser beam that corresponds to that portion of the LTP beam that forms the line image to determine the variation in the amount of power.