Laser Ablation of a fused silica surface

[Sciencestd]

I read in couple of articles, like this one: https://link.springer.com/content/pdf/10.1007/BF00324203.pdf that regions of fused silica surface can be ablated by laser...
I have two questions:

1- Why does the ablation occur?
2- does the ablation happens when the laser waist point is under the surface or deep under the surface?

 

[ZapperZ]

I read in couple of articles, like this one: https://link.springer.com/content/pdf/10.1007/BF00324203.pdf that regions of fused silica surface can be ablated by laser...
I have two questions:

1- Why does the ablation occur?
2- does the ablation happens when the laser waist point is under the surface or deep under the surface?

Laser ablation occurs in practically all substance, not just for fused silica. It is a very common thin film deposition technique.

Are you asking more about the technique, or is there a question specific to fused silica in particular?

Zz.

 

[Sciencestd]

Laser ablation occurs in practically all substance, not just for fused silica. It is a very common thin film deposition technique.

Are you asking more about the technique, or is there a question specific to fused silica in particular?

Zz.

Thank you so much for your comment, I think it is more on technique but maybe it is related more to fused silica because I use fused silica... the question is why when the focal point of the laser is under the surface the ablation doesn't occur? (Actually when it is much below the surface and not just below the surface..)

 

[ZapperZ]

Thank you so much for your comment, I think it is more on technique but maybe it is related more to fused silica because I use fused silica... the question is why when the focal point of the laser is under the surface the ablation doesn't occur? (Actually when it is much below the surface and not just below the surface..)

But do you know what "laser ablation" is in the first place? That is what I'm trying to find out first.

There is no point is teaching you how to run a sprint when you don't know how to walk just yet. See what I mean?

Laser ablation is, naively, "heating and vaporizing using laser". It is why you want the focus to be on the surface that you want to ablate because that is where you get the highest energy density from the laser. This is true for anything you want to ablate, not just fused silica.

Zz.

 

[Sciencestd]

I know what ablation is, but maybe I didn't explain myself well..., Why should nothing really occur when the focus inside the bulk (material) far from the surface?

 

[ZapperZ]

I know what ablation is, but maybe I didn't explain myself well..., Why should nothing really occur when the focus inside the bulk (material) far from the surface?

Were you never a naughty child who tried to see what would happen if you focused sunlight using a magnifying glass onto an bug?

Zz.

 

[Sciencestd]

I used magnifying glass onto a paper it was so thin :P. It seems my question was not close to what I meant 🙈🙉🙊, anyway can you guess what will happen inside the bulk then?

 

[ZapperZ]

I used magnifying glass onto a paper it was so thin :P. It seems my question was not close to what I meant 🙈🙉🙊, anyway can you guess what will happen inside the bulk then?

Why should anything happen inside the bulk material if nothing happens on the surface? I'm assuming we're still talking about the ablation process. You have light in a material with a different index of refraction, and the material may also start to scatter the photons. Depending on the laser wavelength, it may just pass through without doing anything. But even if there's enough energy to cause vaporization inside the material, none of it will probably be released, or at least, it is not significant enough that this is how you want to do a laser-ablation process.

Zz.

 

[Sciencestd]

Thank you so much for your answers :)

 

[crashcat]

1. It is key for laser ablation that the laser is pulsed with high peak power. If you would use a CW laser, the glass would melt instead. The focused, pulsed laser with high peak power doesn't melt the surface. Locally, the atoms in the glass are given so much energy that they enter the vapor phase and leave the surface. They don't give their heat to their neighbors because there is no time for that relaxation process. This implies that it is the peak power (W/cm^2) that is key for the ablation process, and it only works at the beam waist.

2. If the laser was focused below the surface, some would be absorbed above but there is probably still enough energy at the waist to vaporize. However, the atoms are stuck within the bulk and cannot escape. They cool, redeposit, and their energy is given to their neighbors. So all you're doing is heating/melting.

 

[Sciencestd]

Thank a lot you for the answer :)