Laser removal of poor thermally-conductive materials

Abstract

A method of removing material of poor thermal conductivity such as paint, grease, ceramics, and the like from a substrate by ablation without damage to the substrate by delivering to the material to be removed pulses or their equivalent of a laser beam having a wavelength at which the material to be removed is opaque and a fluence sufficient to ablate or decompose the material without damaging or adversely affecting the substrate or its surface.

I claim: 
     
       1. The method of removing by ablation at least one layer of paint disposed directly on and carried by a substrate without adversely affecting the paint carrying surface of said substrate, comprising: (a) generating a pulsed laser beam having a wavelength that is at least substantially absorbed by said paint, the pulses of said laser beam having a length greater than about three microseconds and less than about four thousand microseconds and a repetition rate of greater than about one and less than about one thousand pulses per second;   (b) causing said laser beam to impinge on and to move over said paint;   (c) providing in said laser beam pulses, energy greater than about two and less than about one hundred joules per square centimeter, said pulse terminating before at least a substantial portion of the energy in said pulse diffuses away from the surface of said paint;   (d) controlling the travel of said laser beam over said paint to effect delivery of a plurality of pulses of said laser beam energy to sequential portions of said paint in a time to limit the total energy applied per square centimeter to not greater than about one hundred joules per square centimeter of about each 0.003 inches of paint thickness whereby said paint is ablated without substantially adversely affecting the paint carrying surface of said substrate, said plurality of pulses being delivered to each sequential portion within a predetermined period of time whereby at least substantially all of said paint in each portion is removed without substantially adversely affecting said substrate, said pulse repetition rate is substantially greater than the rate at which said number of pulses is delivered to each sequential portion, the predetermined rate at which said number of pulses is delivered to each sequential portion substantially defines a fraction of the said pulse repetition rate, and said laser beam is caused to sequentially travel over a number of portions substantially equal to the reciprocal of said fraction and return to the first of such number of portions until said plurality of pulses are delivered to each said portion.   
     
     
       2. The method as defined in claim 1 wherein said substrate is composed of a nonmetallic composite material. .Iadd.3. The method of removing by ablation at least one layer of paint disposed directly on and carried by a substrate without adversely affecting the paint carrying surface of said substrate, comprising: (a) generating a pulsed laser beam having a wavelength that is substantially absorbed by said paint, the pulses of said laser beam having a length greater than about three microseconds and less than about four thousand microseconds and having a predetermined repetition rate;   (b) causing said laser beam to impinge on and to move over said paint;   (c) providing in said laser beam pulses, energy greater than about two and less than about one hundred joules per square centimeter, said pulse terminating before at least a substantial portion of the energy in said pulse diffuses away from the surface of said paint;   (d) controlling the travel of said laser beam over said paint to effect delivery of a plurality of pulses of said laser beam energy to sequential portions of said paint in a time to limit the total energy applied per square centimeter to not greater than about one hundred joules per square centimeter of about each 0.003 inches of paint thickness whereby said paint is ablated without substantially adversely affecting the paint carrying surface of said substrate, said plurality of pulses being delivered to each sequential portion within a predetermined period of time whereby at least substantially all of said paint in each portion is removed without substantially adversely affecting said substrate, said pulse repetition rate is substantially greater than the rate at which said number of pulses is delivered to each sequential portion, the predetermined rate at which said number of pulses is delivered to each sequential portion substantially defines a fraction of the said pulse repetition rate, and said laser beam is caused to sequentially travel over a number of portions substantially equal to the reciprocal of said fraction and return to the first of such number of portions until said plurality of pulses are delivered to each said portion. .Iaddend.   
     
     
        .Iadd.    In a method of removing paint from a substrate without adversely affecting the substrate including the steps of generating a laser beam having a wavelength that is substantially absorbed by the paint, causing the laser beam to impinge upon and move over the paint, and controlling the travel of the laser beam over the paint to deliver a predetermined plurality of pulses of laser beam to portions of said paint sufficient to ablate said paint from said portions, wherein the improvement comprises: delivering a first plurality of pulses to sequential portions of said paint within a predetermined period of time, said first plurality of pulses for each portion being less than said predetermined plurality of pulses to ablate paint from each portion and, delivering at least one additional plurality of pulses to at least some of said sequential portions by returning said laser beam to said sequential portions and delivering at least a second plurality of pulses to said sequential portions until the number of pulses delivered to at least one of said sequential portions substantially equals said predetermined plurality of pulses. .Iaddend.   
     
     
        .Iadd.5.  A method of removing poor thermally-conductive material from a substrate without substantially adversely affecting the substrate, the method comprising the steps of: generating a pulsed laser beam having a wavelength that is substantially absorbed by said material, each pulse of said laser beam having a pulse length of between about three and about four thousand microseconds and having a pulse repetition rate greater than one pulse per second;   causing said laser beam to impinge upon and move over said material;   providing in each of said laser beam pulses energy of about two to about one hundred joules per square centimeter; and   controlling the movement of said laser beam over said material for delivering a first series of a first plurality of pulses to different portions of said paint in a sequential manner, said first plurality of pulses being less than a required predetermined plurality of pulses to ablate material from said substrate, and returning said laser beam to a beginning of said different portions and delivering at least one additional series of a plurality pulses until said material is ablated. .Iaddend.