Method and apparatus for optimally laser marking articles

Abstract

The present invention relates to laser marking articles. In particular it relates to laser marking articles by laser ablating a coating applied to the article which reveals the surface of the article underneath, thereby forming the mark by the contrasting appearance between the revealed surface of the article and the adjacent remaining coating. Laser parameters are selected to provide uniform, commercially desirable appearance and avoid damage to the underlying surface while maintaining acceptable system throughput. In particular the laser pulse envelope is tailored to provide desirable appearance while maintaining acceptable system throughput.

1 . A method for compensating for a decreased damage threshold of a specimen caused by residual heating along a laser tool path, comprising:
 generating from a laser, a laser beam of laser pulses having at least one of selectable power, repetition rate, pulse temporal shape, and pulse duration;   directing the laser beam a long an optical path including laser optics;   supporting the specimen on a motion stage;   employing along the optical path, an optical head cooperative with motion control elements operable to position the laser beam along the laser tool path with respect to the specimen;   employing a system controller operatively connected to the laser and the motion control elements, wherein the controller is operable to control laser pulse parameters operative for marking the specimen, wherein the laser pulse parameters include fluence information associated with creating the mark having the desired properties, wherein the fluence information includes first and second fluence information, wherein the first fluence information is associated with a first laser fluence for use in a first portion of a laser beam stroke along the tool path, wherein the second fluence information is associated with a second laser fluence for use in a second portion of the laser beam stroke along the tool path, wherein the second laser fluence is adapted to compensate for a decreased damage threshold of the specimen along the tool path based on calculated residual heating caused by application of the first laser fluence in the first portion of the laser beam stroke along the tool path;   employing along the optical path, an extra-cavity controllable beam attenuator that is operative to attenuate said laser beam;   employing an attenuator controller operative to cause the controllable beam attenuator to attenuate the laser beam at a first attenuation level to provide a first group of first laser output pulses at a first predetermined non-zero power level based on the laser pulse parameters controlled by, and/or stored in, the system controller, and operative to cause the controllable beam attenuator to attenuate the laser beam at a second attenuation level to provide a second group of second laser output pulses at a second predetermined non-zero power level based on the laser pulse parameters controlled by, and/or stored in, the system controller, wherein the first group of first laser output pulses precedes the second group of second laser output pulses of the laser beam strokes, wherein the first predetermined non-zero power level is greater than the second predetermined non-zero power level, wherein the system controller is configured to coordinate operation of the laser, the motion control elements, and the attenuator controller so as to direct the first laser fluence in the first portion of the laser beam stroke along the tool path and direct the second laser fluence in the second portion of the laser beam stroke along the tool path to compensate for the decreased damage threshold of the specimen along the tool path based on the calculated residual heating caused by application of the first laser fluence in the first portion of the laser beam stroke along the tool path, thereby creating the mark having the desired properties.   
     
     
         2 . The method of  claim 1 , wherein said first and second laser pulses comprise pulse fluence ranges from 1.0×10 −6  Joules/cm 2  to 1.0 Joules/cm 2 . 
     
     
         3 . The method of  claim 1 , wherein implementation of the first and second attenuation levels is operable to permit the controller to control fluence of the first and second laser output pulses applied to the specimen without requiring the laser to be turned on and off. 
     
     
         4 . The method of  claim 1 , wherein the system controller is operative to implement a tool path calculated to provide a maximum removal rate without damaging the specimen. 
     
     
         5 . The method of  claim 1 , wherein said specimen is coated with first and second layers of applied coatings and said desired properties of said mark comprise removing said first layer without damaging said second layer. 
     
     
         6 . The method of  claim 5 , wherein the coatings have ablation and damage thresholds that vary depending on location. 
     
     
         7 . The method of  claim 5 , wherein the coatings have ablation and damage thresholds that vary as a function of time and heat generated by marking of the specimen. 
     
     
         8 . The method of  claim 5 , wherein the first layer overlies the second layer, wherein the first and second layers of applied coatings have different ablation thresholds, and wherein the first layer has an ablation threshold that is lower than that of the second layer. 
     
     
         9 . The method of  claim 1 , further comprising:
 employing an electronic circuit operative to receive an input signal from the system controller, wherein the input signal is operative to indicate initiation of each of a plurality of laser beam strokes on the specimen, wherein the electronic circuit is operative to pass the input signal to a trigger signal input of the attenuator controller to activate the controllable beam attenuator to transmit laser pulses of the laser beam selected by the system controller to perform laser beam strokes on the specimen, wherein the electronic circuit is operative to deliver an analog voltage to an analog voltage input of the attenuator controller such that the attenuator controller is operative to emit a proportion signal to the controllable beam attenuator to cause the controllable beam attenuator to adjust energy of the laser pulses in proportion to the analog voltage delivered to the analog voltage input, such that the electronic circuit is operative to tailor the first and second laser output pulses to exhibit the respective first and second predetermined non-zero power levels.   
     
     
         10 . The method of  claim 9 , wherein the electronic circuit further comprises:
 a pulse circuit operative to receive the input signal from the system controller, and wherein the pulse circuit is operable to produce a pulse of programmable duration.   
     
     
         11 . The method of  claim 10 , wherein the electronic circuit further comprises:
 an amplifier operative to receive the pulse of programmable duration and amplify it to provide an amplified pulse at a programmable voltage level;   a signal-conditioning filter operative to receive and condition the amplified pulse to provide a conditioned signal; and   a summation circuit operative to receive and combine the conditioned signal with a pulse voltage output from the system controller to provide the analog voltage delivered to the analog input of the attenuator controller.   
     
     
         12 . The method of  claim 10 , wherein the electronic circuit further comprises:
 an amplifier positioned upstream of the analog voltage input and operative to receive the a pulse voltage output from the system controller and to amplify the pulse voltage output to provide an amplified pulse voltage output;   an analog switch operative to receive the pulse of programmable duration from the pulse circuit and the amplified pulse voltage output from the amplifier and operative to transmit a gated amplified analog signal;   a signal-conditioning filter operative to receive and condition the gated amplified analog signal to provide a conditioned signal; and   a summation circuit operative to receive and combine the conditioned signal with the pulse voltage output from the system controller to provide the analog voltage delivered to the analog input of the attenuator controller.   
     
     
         13 . The method of  claim 1 , wherein the extra-cavity controllable beam attenuator comprises an acousto-optic modulator (AOM), and wherein the attenuator controller comprises an AOM controller. 
     
     
         14 . The method of  claim 9 , wherein the extra-cavity controllable beam attenuator comprises an acousto-optic modulator (AOM), and wherein the attenuator controller comprises an AOM controller. 
     
     
         15 . The method of  claim 10 , wherein the extra-cavity controllable beam attenuator comprises an acousto-optic modulator (AOM), and wherein the attenuator controller comprises an AOM controller. 
     
     
         16 . The method of  claim 11 , wherein the extra-cavity controllable beam attenuator comprises an acousto-optic modulator (AOM), and wherein the attenuator controller comprises an AOM controller. 
     
     
         17 . The method of  claim 1 , wherein the controller is configured to store predetermined laser pulse parameters operative for marking the specimen, wherein the attenuator controller is operative to cause the controllable beam attenuator to attenuate the laser beam at the first attenuation level to provide the first group of first laser output pulses at the first predetermined non-zero power level based on the laser pulse parameters stored in the system controller, and wherein the attenuator controller is operative to cause the controllable beam attenuator to attenuate the laser beam at the second attenuation level to provide the second group of second laser output pulses at the second predetermined non-zero power level based on the laser pulse parameters stored in the system controller. 
     
     
         18 . The method of  claim 9 , wherein the controller is configured to store predetermined laser pulse parameters operative for marking the specimen, wherein the attenuator controller is operative to cause the controllable beam attenuator to attenuate the laser beam at the first attenuation level to provide the first group of first laser output pulses at the first predetermined non-zero power level based on the laser pulse parameters stored in the system controller, and wherein the attenuator controller is operative to cause the controllable beam attenuator to attenuate the laser beam at the second attenuation level to provide the second group of second laser output pulses at the second predetermined non-zero power level based on the laser pulse parameters stored in the system controller. 
     
     
         19 . The method of  claim 1 , wherein the first group of first laser output pulses occurs at the beginning of the laser beam strokes and the second group of second laser output pulses occurs at the remainder of the laser beam strokes. 
     
     
         20 . A method for compensating for a decreased damage threshold of a specimen caused by residual heating along a laser tool path, comprising:
 generating from a laser, a laser beam of laser pulses having at least one of selectable power, repetition rate, pulse temporal shape, and pulse duration;   directing the laser beam a long an optical path including laser optics;   supporting the specimen on a motion stage;   employing along the optical path, an optical head cooperative with motion control elements operable to position the laser beam along the laser tool path with respect to the specimen;   employing a system controller operatively connected to the laser, the motion control elements, and the motion stage, wherein the controller is operable to control laser pulse parameters operative for marking the specimen, wherein the laser pulse parameters include fluence information associated with creating the mark having the desired properties, wherein the fluence information includes first and second fluence information, wherein the first fluence information is associated with a first laser fluence for use in a first portion of a laser beam stroke along the tool path, wherein the second fluence information is associated with a second laser fluence for use in a second portion of the laser beam stroke along the tool path, wherein the second laser fluence is adapted to compensate for a decreased damage threshold of the specimen along the tool path based on calculated residual heating caused by application of the first laser fluence in the first portion of the laser beam stroke along the tool path;   employing along the optical path, an extra-cavity controllable beam attenuator that is operative to attenuate said laser beam;   employing an attenuator controller operative to cause the controllable beam attenuator to attenuate the laser beam at a first attenuation level to provide a first group of first laser output pulses at a first predetermined non-zero power level based on the laser pulse parameters controlled by, and/or stored in, the system controller, and operative to cause the controllable beam attenuator to attenuate the laser beam at a second attenuation level to provide a second group of second laser output pulses at a second predetermined non-zero power level based on the laser pulse parameters controlled by, and/or stored in, the system controller; and   employing an electronic circuit operative to receive an input signal from the system controller, wherein the input signal is operative to indicate initiation of each of a plurality of laser beam strokes on the specimen, wherein the electronic circuit is operative to pass the input signal to a trigger signal input of the attenuator controller to activate the controllable beam attenuator to transmit laser pulses of the laser beam selected by the system controller to perform laser beam strokes on the specimen, wherein the electronic circuit is operative to deliver an analog voltage to an analog voltage input of the attenuator controller such that the attenuator controller is operative to emit a proportion signal to the controllable beam attenuator to cause the controllable beam attenuator to adjust energy of the laser pulses in proportion to the analog voltage delivered to the analog voltage input, such that the electronic circuit is operative to tailor the first and second laser output pulses to exhibit the respective first and second predetermined non-zero power levels such that the first group of first laser output pulses precedes the second group of second laser output pulses of the laser beam strokes, and such that the first predetermined non-zero power level is greater than the second predetermined non-zero power level, wherein the system controller is configured to coordinate operation of the laser, the stage, the motion control elements, and the attenuator controller so as to direct the first laser fluence in the first portion of the laser beam stroke along the tool path and direct the second laser fluence in the second portion of the laser beam stroke along the tool path to compensate for the decreased damage threshold of the specimen along the tool path based on the calculated residual heating caused by application of the first laser fluence in the first portion of the laser beam stroke along the tool path, thereby creating the mark having the desired properties.