Laser ablation or photoablation (also called laser blasting) is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...

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 Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...

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. While relatively long laser pulses (e.g. nanosecond pulses) can heat and thermally alter or damage the processed material, ultrashort laser pulses (e.g. femtoseconds) cause only minimal material damage during processing due to the ultrashort light-matter interaction and are therefore also suitable for micromaterial processing. Excimer lasers of deep ultra-violet light are mainly used in photoablation; the wavelength of laser used in photoablation is approximately 200 nm.

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

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

and pulse length. The total mass ablated from the target per laser pulse is usually referred to as ablation rate. Such features of laser radiation as laser beam scanning velocity and the covering of scanning lines can significantly influence the ablation process. Laser pulses can vary over a very wide range of duration ( milliseconds to

femtosecond A femtosecond is a unit of time in the International System of Units (SI) equal to 10 or of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. For context, a femtosecond is to a second as a second is to about 31 ...

s) 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 drilling Laser drilling is the process of creating thru-holes, referred to as “popped” holes or “percussion drilled” holes, by repeatedly pulsing focused laser energy on a material. The diameter of these holes can be as small as 0.002” (~50 μm). ...

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 is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, ...

( laser dentistry). Several workers have employed laser ablation and gas condensation to produce nano particles of metal, metal oxides and metal carbides. 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. In some industries laser ablation may be referred to as laser cleaning. Narran ROD

One of the advantages is that no solvents are used, therefore it is environmentally friendly and operators are not exposed to chemicals (assuming nothing harmful is vaporized). It is relatively easy to automate. The running costs are lower than dry media or

dry-ice blasting Dry-ice blasting is a form of carbon dioxide cleaning, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it. The method is similar to other forms of media b ...

, 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 A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

. Laser cleaning is also used for efficient rust removal from iron objects; oil or grease removal from various surfaces; restoration of paintings, sculptures, frescoes. Laser ablation is one of preferred techniques for rubber mold cleaning due to minimal surface damage to the mold. In March 1995 Guo et al. were the first to report the use of a

to ablate a block of pure

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

, and later graphite mixed with catalytic

metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...

. The catalytic metal can consist of elements such as

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

, niobium,

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

, 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

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...

gas is pumped along the direction of the laser point. The oven temperature is approximately 1200 °C. As the laser ablates the target,

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 called pulsed laser deposition (PLD), 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 High-temperature superconductors (abbreviated high-c or HTS) are defined as materials that behave as superconductors at temperatures above , the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previo ...

and laser crystals. Remote laser

spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...

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. Laser ablation is also used to create pattern, removing selectively coating from dichroic filter. This products are used in stage lighting for high dimensional projections, or for calibration of machine vision's instruments.

Propulsion

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.

Manufacturing

Processes are currently being developed to use laser ablation in the removal of thermal barrier coating on high-pressure gas turbine components. Due to the low heat input, TBC removal can be completed with minimal damage to the underlying metallic coatings and parent material.

2D materials production

Laser ablation in the liquid phase is an efficient method to exfoliate bulk materials into their 2-dimensional (2D) forms, such as black phosphorus. By changing the solvent and laser energy, the thickness and lateral size of the 2D materials can be controlled.

Chemical analysis

Laser ablation is used as a sampling method for elemental and isotopic analysis, and replaces traditional laborious procedures generally required for digesting solid samples in acid solutions. Laser ablation sampling is detected by monitoring the photons emitted at the sample surface - a technology referred to as LIBS (Laser Induced Breakdown Spectroscopy) and LAMIS (Laser Ablation Molecular Isotopic Spectrometry), or by transporting the ablated mass particles to a secondary excitation source, like the inductively coupled plasma. Both mass spectroscopy (MS) and optical emission spectroscopy (OES) can be coupled with the ICP. The benefits of laser ablation sampling for chemical analysis include no sample preparation, no waste, minimal sample requirements, no vacuum requirements, rapid sample-analysis turn-around time, spatial (depth and lateral) resolution, and chemical mapping. Laser ablation chemical analysis is viable for practically all industries, such as mining, geochemistry, energy, environmental, industrial processing, food safety, forensic and biological. Commercial instruments are available for all markets to measure every element and isotope within a sample. Some instruments combine both optical and mass detection to extend the analysis coverage, and dynamic range in sensitivity.

Biology

Laser ablation is used in science to destroy nerves and other tissues to study their function. For example, a species of pond snail, '' Helisoma trivolvis'', can have their sensory neurons laser ablated off when the snail is still an embryo to prevent use of those nerves. Another example is the trochophore larva of '' Platynereis dumerilii'', where the larval eye was ablated and the larvae was not phototactic, anymore. However phototaxis in the nectochaete larva of ''Platynereis dumerilii'' is not mediated by the larval eyes, because the larva is still phototactic, even if the larval eyes are ablated. But if the adult eyes are ablated, then the nectochaete is not phototactic anymore and thus phototaxis in the nectochaete larva is mediated by the adult eyes. Laser ablation can also be used to destroy individual cells during

embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

of an organism, like ''Platynereis dumerilii'', to study the effect of missing cells during development.

Medicine

There are several

laser types A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

used in medicine for ablation, including

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

(CO₂),

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

erbium Erbium is a chemical element with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element, ...

, excimer, Nd:YAG, and others. Laser ablation is used in a variety of medical specialties including

ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a me ...

general surgery General surgery is a surgical specialty that focuses on alimentary canal and abdominal contents including the esophagus, stomach, small intestine, large intestine, liver, pancreas, gallbladder, appendix and bile ducts, and often the thy ...

neurosurgery Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and pe ...

ENT Ents are a species of beings in J. R. R. Tolkien's fantasy world Middle-earth who closely resemble trees; their leader is Treebeard of Fangorn forest. Their name is derived from an Old English word for giant. The Ents appear in ''The Lor ...

, dentistry, oral and maxillofacial surgery, and veterinary. Laser scalpels are used for ablation in both hard- and soft-tissue surgeries. Some of the most common procedures where laser ablation is used include

LASIK LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism (eye), ...

, skin resurfacing, cavity preparation,

biopsies A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a disea ...

, and tumor and lesion removal. In soft-tissue surgeries, the CO₂ laser beam ablates and cauterizes simultaneously, making it the most practical and most common soft-tissue laser. Laser ablation can be used on benign and malignant lesions in various organs, which is called laser-induced interstitial thermotherapy. The main applications currently involve the reduction of benign thyroid nodules and destruction of primary and secondary malignant liver lesions. Laser ablation is also used to treat

chronic venous insufficiency Chronic venous insufficiency (CVI) is a medical condition in which blood pools in the veins, straining the walls of the vein. The most common cause of CVI is superficial venous reflux which is a treatable condition. As functional venous valves are ...

. See also ablative brain surgery.

References

Bibliography

*Oxford Concise Medical Dictionary,2002,6th edition, {{Lasers

Ablation Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...

Laser applications Plasma physics Laser medicine Medical treatments