Laser ablation is the process of removing material from a  solid substance. Many different laser types are used, and the technique  can be applied to virtually any class of material – metals,  semiconductors, glass, ceramics, polymers, wood, stone, tissue and other  biological materials.

Lasers are used for selective material removal in an extremely  broad range of applications – from the production of advanced integrated  circuit packaging to corneal reshaping to making plastic signs. But in  all these diverse applications, lasers tend to deliver similar benefits  that distinguish them from other technologies. These include:

Spatial selectivity

This  is the ability to precisely remove material over a predefined area, and  to a well-controlled depth, and to produce intricate patterns or fine  detail.

Small heat affected zone (HAZ)

Depending upon the material and laser  type, laser ablation can be performed without significantly changing or  damaging the area surrounding where material removal occurs.

Non-contact processing

Since laser processing doesn’t apply  any mechanical force or pressure on the work piece, it can be used on  small or delicate parts. This also tends to reduce the tooling  requirements for most applications.

Process flexibility

Laser ablation doesn’t usually require  specialized tooling and is almost always performed under computer  control. This makes it easy to change. For example, in many laser  etching or engraving applications, every single part receives a unique  pattern or mark.

Laser ablation methods

While laser ablation delivers similar advantages in many  applications,  the technique works via a range of methods. These depend  upon the laser type, the material itself, and the job requirements.  Broadly speaking, though, all ablation processes operate through  photothermal or photoablative interactions. It’s not uncommon for a  combination of the two to occur within a single process.

In a photothermal process, material is removed by intense, spatially  confined heating. Essentially the substance is rapidly heated until  material is either boiled off or sublimated (directly transformed from  solid to gas or plasma, without going through an intervening liquid  phase).

Photothermal processing typically puts a fair amount of heat into the  work piece. So, it’s not usually used with heat sensitive parts(with  materials that have high thermal conductivity), or on smaller work  pieces (where the heat can readily reach other areas of the part).  Photothermal processing typically offers relatively rapid material  removal rates making it useful in high throughput production  applications and those that cover large areas.

The second method – photoablation – involves directly breaking the  molecular or atomic bonds which hold a material together, rather than  heating it. This makes it a “cold” process. There are generally two ways  to achieve this bond breaking.

• The first relies on linear absorption in the material of a photon  having greater energy than its chemical bond energy. This virtually  always relies on ultraviolet (UV) lasers, because only UV photons supply  enough energy for bond breaking in most solids. This is because photon  energy increases as wavelength decreases, and UV light has a shorter  wavelength than visible or infrared light.

• The second way to cause photoablation is with a laser that has  sufficiently high peak pulse power to drive non-linear absorption. In  this kind of “multiphoton” process, the material absorbs the laser  energy even if it is normally transparent at that laser wavelength. The  peak powers required to drive non-linear absorption can usually only be  achieved using an ultra-short pulse (USP) laser.

Photoablation is used for the highest precision applications and  those which require the smallest HAZ (often just 10s of microns).  However, the material removal rates are generally much lower than for  photothermal ablation. And the USP sources are typically larger and more  costly than the lasers used for photothermal processes.