I want to learn about different time zone laser ablation. what are the applications corresponds to these individually ?
Theoretical model of laser ablation (at least one of them) is called two temperature model. And it speaks separately about temperature (kinetic energy) of electrons and of nucleis. Basically it says the following: First electrons absorb the optical energy, and either in a ladder like manner (for longer pulses) or by direct multi-photon process (for shorter ones) are getting out of bound states to continuum. Now two things can happen to the electron:
1. It will collide with a nuclei ant transfer its energy to phonons (thermalization)
After many collisions, nuclei will gain enough energy to escape the bulk
2. Electrons are gaining lots and lots of energy and leave the material (kind of multi-photon photoelectric effect). Nuclei stay cool. But after enough electrons have left, the nuclei remain unbound, and "fly away" due to room temperature energy.
The second mechanism, obviously affects much less area. In fact, being naturally multi-photon, the ablated area is proportional to intensity in the optical spot size in high power, effectively making the "hole" smaller.
This second type of ablation is claimed to be used in medical devices for ophthalmology, where the size of the perforation is most critical.
As far as I remember it was nice series of experiments shown by P. Bucksbaum at Stanford, using ultra-fast femtosecond ablation followed by ultra-short x-ray diffraction, where they have verified the second mechanism. I would check about years 2005-2009, but not sure exactly.
Here is more recent paper, that looks relevant:
Optics Express, Vol. 20, Issue 28, pp. 29329-29337 (2012)
In practical use for fs and ps pulses there is an interaction with a substrate. In a case with ns and mc pulses interaction both with a substrate and with plasma proceeds.
Just to add some practical issues: fs ablation although allows to achieve smaller holes, but often suffers oh rather strange shapes. That is due to the fact that removed material is cold as is the surrounding substrate. So it tends to crystalize on the hole edges, producing lots of debris around.
the nan,fs and ps pulse duration ,the ps sort time,the power is ultra high power,when aim of the study ablation or laser produce plasma or thin film up on the pulse duration and wavelength.
A lot of work has been done at the U of M center CUOS by Dr. Gerard Mourou' s group to compare damage threshold at different pulse duration.
ns mainly and ps to some extend give a random threshold.
Damage to the material done using fs pulses is perfectly defined for a given material.
Hence their use in micromachining and surgery such as the cut of the flap in the Lasik surgical procedure promoted by Intralase Inc.
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