StarLaser ablation is gaining a lot of traction in today's manufacturing sector. This technology's benefits and ease of use far surpass any other alternatives out there. Therefore, professionals and manufacturers who haven't adopted the technology already often enquire about 'what is laser ablation process?' and its functioning and parameters.
This article will have an in-depth discussion on what is laser ablation and the various details associated with this concept. With the information presented here, you can discover all the benefits of laser ablation for your industrial segment.
What is Laser Ablation (Laser Blasting)?
Laser ablation is an industrial process that uses the energy of a laser beam to remove material from a solid or liquid object. This process is also known as laser blasting. A laser beam is a high-energy amplified light ray. When it comes to contact with the unwanted material, the laser's energy is transferred to the particles. The material particles quickly evaporate from the object by gaining energy from the lasers. Ablation is typically carried out by pulsed lasers instead of a continuous wave laser. It can use any laser source generation method such as fiber laser, carbon nanotubes, excimer laser, etc.
A Short History of Laser Ablation
Research into the concept of laser ablation began quickly after the invention of the laser in 1962. The early applications of laser ablation were mostly in the medical sector. For instance, in 1963 McGuff experimented with laser ablation in the areas of cardiovascular surgery. It was later in 1995 when Guo et al. used a laser ablation process for catalytic metal mixed with solidified graphite paste.
How Does Laser Ablation Work?
Laser ablation is a combination of two processes- vaporization and melt expulsion. Here is a detailed breakdown of the various steps involved in the working process of laser ablation:
The process starts with the generation of high-intensity laser pulses. When this light emitted strikes the surface material, the energy of the photons is absorbed by the material particles. The material particles then get heated, which causes an instant vaporization.
The instant conversion of solid material particles to gas creates a plasma plume. While the vaporization feels instant, it is a multi-step process in itself. Initial laser pulses first melt the solid particles into liquid, creating a melt pool. Further pulses turn the melt pool into vapor by exciting the particle electrons.
The vaporization of particles creates high pressure in the direction of the substrate. This pressure pushes away the melt pool formed on the substrate. It is known as recoil pressure.
It is possible to collect the vaporized particles and study them for elemental and isotopic chemical analysis. This is the foundation for multiple scientific processes such as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
The properties of the material particles and the laser govern the depth and speed of ablation. For instance, a shorter laser wavelength, higher frequency of pulses, longer exposure duration, and higher energy density will lead to a faster and deeper ablation. On the material end, the ablation rate is influenced by properties such as thermal conductivity and material layer thickness.
Different Parameters of Laser Ablation
Many technical laser parameters are important to understand when learning laser ablation. These parameters define the properties of the laser and the process.
The laser wavelength is measured in nanometers and represented with the symbol λ. The laser wavelength determines the energy impact and energy transfer efficiency. The laser wavelength is the inverse value of the light frequency. A laser with a shorter wavelength will carry a higher energy. Different types of lasers have different wavelengths.
Laser fluence is defined as the energy of the laser per unit area. It demonstrates the degree of concentration of the laser beam. The laser fluence can also be seen as the energy density of the laser beam. A higher fluence means that a laser beam can remove more depth of material per pulse.
The pulse duration is the time period for which a single laser pulse remains in contact with the material. It is sometimes referred to as the pulse length. While a long pulse duration can carry more energy, a shorter pulse duration is preferred for laser ablation. This keeps the integrity of the substrate whole while carrying enough intensity for the vaporization of the required material layers.
Laser beam quality relates to the ability of the lasers to be focused. This value is measured as M2. It can also be seen as the degree of divergence of a laser beam. Ideally, lasers will have the best beam quality when M2 = 1. Lasers with poor beam quality will also be less efficient due to a higher loss of laser power in divergence from the spot.
Beam diameter is the width of the laser beam. Beam diameter is the value one refers to when talking about the spot size of the laser ablation beam. The beam diameter increases the dispersion of the lasers, resulting in a poor fluence. Increasing the beam diameter beyond a certain point results in no laser ablation. Increasing the beam diameter also increases the chances of laser welding instead of laser ablation. Decreasing the beam diameter results in a higher fluency, increasing the laser ablation rate.
Focal distance is the length between the output of the laser system and the point of focus where the laser light meets the material. The focal distance is varied by interchanging the optics used in the laser ablation methods. Another option to vary the focal distance is by using 3D heads.
Number of Pulses
The number of pulses is the count of pulsed laser light that is delivered to the material. Higher number of pulses increases the depth of the laser ablation.
The laser power is the amount of energy emitted by the laser per unit time. It is expressed in Watts (W). An important thing to understand about laser power is that it is the average power delivered by the laser. Therefore, a 100W pulsed laser deposition does not mean it is delivering 100 W pulses. It can deliver pulses as high as 10,000 W, which are then averaged by the gap between the pulses where there is no light emission. However, in the case of continuous wave laser, the laser power is the maximum power delivered by the pulses. A high laser power leads to a higher fluence.
The scanning speed is the speed at which the laser technology is able to scan the surface material. Scanning is accomplished by moving the laser light through mirrors present inside the laser system. The scanning speed affects the exposure time of the material to the laser light. This, in turn, affects the rate and quality of the laser ablation.
Pulse Repetition Rate
The pulse repetition rate is defined as the number of pulses per second. It is also known as pulse frequency. Since the laser power of a system is fixed, increasing the pulse frequency will increase the number of pulses per second. This will decrease the absorbed laser energy from each pulse since the total energy of the pulses is constant in each second.
Pulse spacing is the length between two successive laser spots during scanning. Having very little pulse spacing will increase the depth of laser ablation. This can also cause penetration in the underlying surface, resulting in laser engraving. Too far pulse spacing can result in missing out on the material between scans.
Number of Passes
The number of passes indicate the number of times a laser scans the same spot. Most materials can be easily ablated in one laser pass. However, the high energy of the laser can cause thermal heating and damage to the underlying material. Therefore, in many cases, multiple passes of laser ablation are carried out by lowering the individual pulse energy.
What are the Different Laser Ablation Methods?
There are many different ways to carry out laser ablation. The different types of laser ablation methods are:
Excimer Laser Ablation
Excimer laser ablation uses ultraviolet (UV) light to break chemical bonds for the ablation process. It is also known as exciplex laser ablation. Excimer laser ablation is very common in micromachining organic materials and sensitive medical surgery. The popular laser eye surgery called LASIK uses excimer laser ablation procedure.
Pulsed Laser Deposition (PLD)
Pulsed Laser Deposition is a type of physical vapor deposition method for depositing a particular material on a substrate. PLD uses laser ablation to remove material from an object as a plasma plume. The plasma plume then deposits on the substrate wafer as a thin layer. The whole process is carried in a vacuum chamber to direct the flow of the plasma plume. Pulsed Laser Deposition is a five-stage process:
Laser absorbed by the targeted area
Creation of plasma plume
Movement of plasma towards the substrate wafer
Deposition of the ablated layers on the surface
Growth of the ablated film
Laser-Induced Forward Transfer (LIFT)
Laser Induced Forward Transfer (LIFT) is a type of printing technique that uses the concept of laser ablation. Generally, it uses a laser to ablate a solid block of ink (called the donor block). This ink is then deposited on a receiving substrate. Lately, it is also common to use liquid ink with laser ablation. The benefit of LIFT is that it is not limited in terms of the particle size and viscosity of the ink being used.
Laser Induced Breakdown Spectroscopy (LIBS)
Laser Induced Breakdown Spectroscopy is a type of scientific chemical analysis method that uses nanosecond pulses laser ablation. Shortening the pulse duration to nanoseconds greatly increases the amount of energy stored in each pulse. The target material can be solid surface, liquid, or even gas. During nanosecond laser ablation, the microplasma formed emits a bright light. This light is captured and studied for further chemical analysis. Different materials have different emission characteristics. Therefore, studying the light emitted can help in a deep chemical analysis of the type of material and its properties.
Ultrafast Laser Ablation
Ultrafast laser ablation uses picosecond or femtosecond laser pulses. When the pulse duration is just a few femtoseconds, the ablation time is less than the time taken for the electron-ion transition. Therefore, ultrafast laser ablation's characteristics differ from alternatives such as nanosecond laser ablation. The primary change is seen in limiting the area of the irradiating laser energy. This avoids damaging the underlying material.
Matrix-assisted Pulsed Laser Evaporation (MAPLE)
Matrix-assisted Pulsed Laser Evaporation is a derivative of Pulsed Laser Deposition technology used for depositing biomaterials and polymers. The MAPLE process isn't used for conventional solid ablation. Instead, it uses laser energy to ablate a frozen solution of a volatile solvent matrix and a pharmacologic compound. The laser ablation process vaporizes the pharmacologic agent and deposits it into thin films on a wafer substrate.
Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS)
Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) is a type of scientific analysis method for studying solid samples using laser ablation. It uses the conventional laser ablation mechanism to generate fine particles of solid samples. These particles are then collected and go through a secondary ionization process in an Inductively Coupled Plasma Mass Spectroscopy setup. The resulting ions are collected in a mass spectrometer for elemental and isotopic chemical analysis.
Laser Ablation Microprobe (LAM)
Laser Ablation Microprobe (LAM) is a type of scientific analysis technique generally used to sample surface of minerals. LAM provides a simple and inexpensive setup for the analysis of various materials. The laser beam is guided through a petrographic microscope phototube to focus it into a particular section. The material that is to be laser ablated is kept on a sample slide.
What are the Applications of Laser Ablation?
Laser ablation is used in many different use cases across the industry. Some of the industrial applications of laser ablation are:
Laser ablation is commonly applied in the medical field in multiple areas. The most common use case is for eye surgery, such as LASIK. These processes also utilize laser cleaning technology.
Laser energy is used for removing permanent tattoo ink by dermatologists. Many other skin treatments also utilize laser ablation.
Laser ablation turns out to be a minimal invasive method for lesion and tumor treatment.
Laser cleaning is one of the most common applications of laser ablation. It can remove layers of oil stains, rust, coatings, and other unwanted materials from the surface of parts.
Laser cleaning can remove unwanted paint coatings from a part without using chemicals.
It can also remove dirt, dust, and other contaminant coatings from an object to prepare surfaces for painting.
Laser etching can create permanent marks on the surface of any object without harming it.
It is common to mark identification numbers on parts, such as QR codes, matrix codes, and characters.
Additive manufacturing commonly uses laser ablation as the deposition technology. The resulting process is called Laser Additive Manufacturing.
Multiple additive manufacturing techniques use laser technology. These are: Selective Laser Sintering (SLS), Stereolithography (SLA), and Selective Laser Melting (SLM).
Laser processing techniques, especially the laser ablation microprobe, is used for the study of minerals and their properties.
The laser texturing process is used for modifying surface finishes.
The prepared surface textures are essential for secondary manufacturing procedures like applying adhesives or paint.
Archaeology and Cultural Heritage
Laser ablation is used for the restoration of ancient artifacts.
The energy from the laser source can remove material such as dirt and solidified minerals from the surface of the artifacts without any risk of damaging the underlying layers.
Electronics and Semiconductors
Laser ablation is common in designing complex integrated circuits for removing material in a high-precision fashion.
It is useful for making fine PCB patterns and drilling micro-vias.
It is vital for thin-film deposition in the semiconductors sector.
Jewelry and Watchmaking
The laser ablation technique is used for marking and engraving jewelry and watches.
Laser cleaning can wipe unwanted oil and dirt from the jewelry surface without harming the underlying sample surface.
Advantages and Disadvantages of Laser Ablation
Laser ablation comes with many benefits and a few limitations. Let us go through each one by one.
What are the advantages of laser ablation?
The benefits of laser ablation are:
It does not require any chemical solvents.
There are minimal thermal heating and heat-affected zones.
It can be precisely controlled and narrowed down to a spot.
It is a versatile method that works on a range of material surfaces.
The speed of laser ablation is very fast.
It can provide selective material removal by adjusting the laser parameters.
There is no harm to the underlying and surrounding material.
What are the disadvantages of laser ablation?
The disadvantages of laser ablation are:
Laser ablation equipment can be costly for certain applications.
Laser ablation requires strict safety protocol due to various hazard risks.
Not adjusting the laser parameters accurately can be damaging to the surface.
What Materials Can Undergo Laser Ablation?
Laser ablation is very versatile regarding the range of supported material surfaces. Some of the materials that can undergo laser ablation are:
Polyethylene Terephthalate (PET)
Polymethyl Methacrylate (PMMA)
Foam core board
Which Machines Use Laser Ablation?
Laser ablation is used by many different machine systems, such as:
Laser Ablation Systems: Laser ablation system is a machine exclusively dedicated to the ablation process. There are no modifications and the primary purpose is to remove material layers.
Laser Micromachining Workstations: Micromachining workstations use laser energy for processes such as laser cleaning, laser cutting, drilling, and restructuring materials at a micro level.
Laser Deposition Machines: Laser deposition machines use ablation as the primary process for removing material. The removed particles are then deposited with secondary mechanisms.
Laser Cleaning: Laser cleaning machines use laser ablation to remove contaminants such as dirt, oils, grease, paints, and oxides. It combines a laser ablation system with a vacuum system for removing the ablated particles.
Laser Engraving Machines: Laser engraving machines use ablation for the process of laser marking.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) Instruments: LA ICP MS instruments combine laser ablation system with mass spectrometry equipment. It is used for material analysis in geology and forensics.
Laser Ablation Nanofabrication System: Laser Ablation Nanofabrication Systems use laser ablation to craft nanostructures on objects. It is a pivotal technology in nanosciences, used for processes such as nanoparticle synthesis.
Laser Ablation Surgical Systems: Surgical systems using pulsed lasers for ablation are common in medicine. It is used for tissue removal and treatment in many medical sciences.
Is Laser Ablation Safe?
Laser ablation has enough power to vaporize very hard materials. Therefore, a proper safety procedure should be followed while using or handling laser ablation machines. The primary safety risk of laser pulses is towards the eyes. Even reflected lasers can cause considerable harm to the eyes. It is vital to wear proper eye protection while using these machines. Additionally, safety gloves are also required in some instances.
Another important safety consideration is the release of toxic fumes. Many materials emit toxic fumes that are a dangerous safety hazard. It is crucial to have a proper ventilation and extraction system and remove and treat such fumes properly.
Are there any environmental concerns associated with laser ablation?
Laser ablation is an environmentally friendly technique with many benefits over alternative processes. For instance, laser ablation does not require any toxic chemicals, reducing hazardous waste generation. However, care must be taken when using laser ablation on a sample surface that can release toxic fumes. Such cases require a proper exhaust system so as to not release hazardous fumes into the environment.
What are the differences between laser ablation and other laser-based processing techniques?
The main difference between laser ablation and any other laser-based processing technique is that laser ablation techniques vaporize the material layers. Other laser-based processing techniques usually intend to melt the material layer into plasma but do not heat it further into vapor. Ablation is possible with higher laser intensity and a more focused light beam.
What Is the Difference Between Laser Ablation and Laser Engraving?
The main difference between laser ablation and laser engraving is that laser ablation is used to remove outermost layers from a surface. On the other hand, laser engraving is used to penetrate a surface to a certain depth to leave permanent markings.
What Is the Difference Between Laser Ablation and Laser Vaporization?
The main difference between laser ablation and laser vaporization is that in laser ablation, the material layer on a surface melts and then begins to vaporize in a very short window of time. In laser vaporization, material surfaces skip the melting stage and directly vaporizes. Laser ablation is used for removing surface layers while laser vaporization is a type of laser cutting used to dig deep holes into a material.
Laser ablation is one of the most innovative technologies with rapid growth in recent years. This process is being applied to emerging sciences such as nanotechnology, spectrometry, and complex surgeries. The applications of laser ablation to fields such as laser cleaning have opened a door into innovative industrial applications that require minimal costs and no chemical raw materials.
Frequently Asked Questions
Here are the answers to some common questions regarding laser ablation:
Is laser ablation a type of laser cutting?
No, laser ablation is not a form of laser cutting. Laser cutting aims to remove material to divide a workpiece into multiple smaller parts. On the other hand, laser ablation is used for vaporizing thin surface layers from an object.
Are there any environmental concerns associated with laser ablation?
Laser ablation is an environmentally friendly technique with many benefits over alternative processes. For instance, laser ablation does not require any toxic chemicals, reducing hazardous waste generation. However, care must be taken when using laser ablation on a sample surface that can release toxic fumes. Such cases require a proper exhaust system to not release hazardous fumes into the environment.
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