Laser ablation
Encyclopedia
Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser
beam. At low laser flux
, the material is heated by the absorbed laser energy and evaporates
or sublimates. At high laser flux, the material is typically converted to a plasma
. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave
laser beam if the laser intensity is high enough.
.
Laser pulses can vary over a very wide range of duration (millisecond
s to femtoseconds) and fluxes, and can be precisely controlled. This makes laser ablation very valuable for both research and industrial applications.
are examples; pulsed lasers can drill extremely small, deep holes through very hard materials. Very short laser pulses remove material so quickly that the surrounding material absorbs very little heat, so laser drilling can be done on delicate or heat-sensitive materials, including tooth enamel
(laser dentistry).
Also, laser energy can be selectively absorbed by coatings, particularly on metal, so CO2 or Nd:YAG pulsed lasers can be used to clean surfaces, remove paint or coating, or prepare surfaces for painting without damaging the underlying surface. High power lasers clean a large spot with a single pulse. Lower power lasers use many small pulses which may be scanned across an area. The advantages are:
Another class of applications uses laser ablation to process the material removed into new forms either not possible or difficult to produce by other means. A recent example is the production of carbon nanotubes.
In March 1995 Guo et al. were the first to report the use of a laser
to ablate a block of pure graphite
, and later graphite mixed with catalytic metal
. The catalytic metal can consist of elements such as Co
, Nb
, Pt
, Ni
, Cu
, or a binary combination thereof. The composite block is formed by making a paste of graphite powder, carbon cement, and the metal. The paste is next placed in a cylindrical mold and baked for several hours. After solidification, the graphite block is placed inside an oven with a laser pointed at it, and Ar
gas is pumped along the direction of the laser point. The oven temperature is approximately 1200°C. As the laser ablates the target, carbon nanotubes form and are carried by the gas flow onto a cool copper collector. Like carbon nanotubes formed using the electric-arc discharge
technique, carbon nanotube fibers are deposited in a haphazard and tangled fashion. Single-walled nanotubes are formed from the block of graphite and metal catalyst particles, whereas multi-walled nanotubes form from the pure graphite starting material.
A variation of this type of application is to use laser ablation to create coatings by ablating the coating material from a source and letting it deposit on the surface to be coated; this is a special type of physical vapor deposition
, and can create coatings from materials that cannot readily be evaporated any other way. This process is used to manufacture some types of high temperature superconductor.
Remote laser spectroscopy
uses laser ablation to create a plasma from the surface material; the composition of the surface can be determined by analyzing the wavelengths of light emitted by the plasma.
Finally, laser ablation can be used to transfer momentum to a surface, since the ablated material applies a pulse of high pressure to the surface underneath it as it expands. The effect is similar to hitting the surface with a hammer. This process is used in industry to work-harden metal surfaces, and is one damage mechanism for a laser weapon. It is also the basis of pulsed laser propulsion
for spacecraft.
The laser ablation of electronic semiconductors and microprocessors is now being pioneered in the UK to keep electronic manufacturers designs confidential
The main reason is that it greatly reduces the risk of copying infringements.
Laser ablation has biological applications and can be used to destroy nerves and other tissues. For example, a species of pond snails, Helisoma trivolvis can have their sensory neurons laser ablated off when the snail is still an embryo to prevent use of those nerves
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
beam. At low laser flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
, the material is heated by the absorbed laser energy and evaporates
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
or sublimates. At high laser flux, the material is typically converted to a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
laser beam if the laser intensity is high enough.
Fundamentals
The depth over which the laser energy is absorbed, and thus the amount of material removed by a single laser pulse, depends on the material's optical properties and the laser wavelengthWavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
.
Laser pulses can vary over a very wide range of duration (millisecond
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
s to femtoseconds) and fluxes, and can be precisely controlled. This makes laser ablation very valuable for both research and industrial applications.
Applications
The simplest application of laser ablation is to remove material from a solid surface in a controlled fashion. Laser machining and particularly laser drillingLaser drilling
Manufacturers of turbine engines for aircraft propulsion and for power generation have benefited from the productivity of lasers for drilling small cylindrical holes at 15-90º to the surface in cast, sheet metal and machined components...
are examples; pulsed lasers can drill extremely small, deep holes through very hard materials. Very short laser pulses remove material so quickly that the surrounding material absorbs very little heat, so laser drilling can be done on delicate or heat-sensitive materials, including tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
(laser dentistry).
Also, laser energy can be selectively absorbed by coatings, particularly on metal, so CO2 or Nd:YAG pulsed lasers can be used to clean surfaces, remove paint or coating, or prepare surfaces for painting without damaging the underlying surface. High power lasers clean a large spot with a single pulse. Lower power lasers use many small pulses which may be scanned across an area. The advantages are:
- No solvents are used, so it is environmentally friendly and operators are not exposed to chemicals.
- It is relatively easy to automate, e.g., by using robots.
- The running costs are lower than dry media or CO2 ice blasting, although the capital investment costs are much higher.
- The process is gentler than abrasive techniques, e.g. carbon fibres within a composite material are not damaged.
- Heating of the target is minimal.
Another class of applications uses laser ablation to process the material removed into new forms either not possible or difficult to produce by other means. A recent example is the production of carbon nanotubes.
In March 1995 Guo et al. were the first to report the use of a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
to ablate a block of pure graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, and later graphite mixed with catalytic metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
. The catalytic metal can consist of elements such as Co
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
, Nb
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
, Pt
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, Ni
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, Cu
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, or a binary combination thereof. The composite block is formed by making a paste of graphite powder, carbon cement, and the metal. The paste is next placed in a cylindrical mold and baked for several hours. After solidification, the graphite block is placed inside an oven with a laser pointed at it, and Ar
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
gas is pumped along the direction of the laser point. The oven temperature is approximately 1200°C. As the laser ablates the target, carbon nanotubes form and are carried by the gas flow onto a cool copper collector. Like carbon nanotubes formed using the electric-arc discharge
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
technique, carbon nanotube fibers are deposited in a haphazard and tangled fashion. Single-walled nanotubes are formed from the block of graphite and metal catalyst particles, whereas multi-walled nanotubes form from the pure graphite starting material.
A variation of this type of application is to use laser ablation to create coatings by ablating the coating material from a source and letting it deposit on the surface to be coated; this is a special type of physical vapor deposition
Physical vapor deposition
Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...
, and can create coatings from materials that cannot readily be evaporated any other way. This process is used to manufacture some types of high temperature superconductor.
Remote laser spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
uses laser ablation to create a plasma from the surface material; the composition of the surface can be determined by analyzing the wavelengths of light emitted by the plasma.
Finally, laser ablation can be used to transfer momentum to a surface, since the ablated material applies a pulse of high pressure to the surface underneath it as it expands. The effect is similar to hitting the surface with a hammer. This process is used in industry to work-harden metal surfaces, and is one damage mechanism for a laser weapon. It is also the basis of pulsed laser propulsion
Laser propulsion
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass...
for spacecraft.
The laser ablation of electronic semiconductors and microprocessors is now being pioneered in the UK to keep electronic manufacturers designs confidential
The main reason is that it greatly reduces the risk of copying infringements.
Laser ablation has biological applications and can be used to destroy nerves and other tissues. For example, a species of pond snails, Helisoma trivolvis can have their sensory neurons laser ablated off when the snail is still an embryo to prevent use of those nerves
See also
- Laser interstitial thermal therapyLaser interstitial thermal therapyLaser interstitial thermal therapy is a surgical procedure in which destruction of soft tissues in the body is effected through high temperatures generated by the local absorption of laser energy...
- Parts cleaningParts cleaningParts cleaning is essential to many industrial processes, as a prelude to surface finishing or to protect sensitive components. Electroplating is particularly sensitive to part cleanliness, since molecular layers of oil can prevent adhesion of the coating. ASTM B322 is a standard guide for cleaning...
- Matrix-assisted laser desorption/ionizationMatrix-assisted laser desorption/ionizationMatrix-assisted laser desorption/ionization is a soft ionization technique used in mass spectrometry, allowing the analysis of biomolecules and large organic molecules , which tend to be fragile and fragment when ionized by more conventional ionization methods...
- Laser induced breakdown spectroscopyLaser induced breakdown spectroscopyLaser-induced breakdown spectroscopy is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. In principle, LIBS can analyse any matter regardless of its physical state,...
- Laser surgeryLaser surgeryLaser surgery is surgery using a laser to cut tissue instead of a scalpel. Examples include the use of a laser scalpel in otherwise conventional surgery, and soft tissue laser surgery, in which the laser beam vaporizes soft tissue with high water content...
- Laser cuttingLaser cuttingLaser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...
- Laser engravingLaser engravingLaser engraving, or laser marking, is the practice of using lasers to engrave or mark an object. The technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface and wear out...
- Laser bondingLaser bondingLaser bonding is a marking technique that uses lasers and other forms of radiant energy to bond an additive marking substance to a wide range of substrates....
- Optical breakdown photoionization mode (OB) at Photoionization modePhotoionization modeA photoionization mode is a mode of interaction between a laser beam and matter, giving rise to a photoionization pattern, having very specific characteristics in terms of photoionization spatial distribution and density, as well as relative yields of photolytic species...