Landau Days 2015
Landau Days 2015
Thin films under the action of short laser pulses
Date/Time: 17:25 23-Jun-2015
We consider laser peeling and structure formation of thin films on substrate.
Let us present shortly a general picture of laser structuring.
It is known, that the structuring of materials by short laser pulses with duration in the range of 10 fs - 1 ps has many important technological applications.
But underlying physics is not well understood.
On our view, the corresponding processes are interplay of plasmon enhanced absorption from one side and a thermomechanical triplet from the another side, where the triplet is: (i) spallation, (ii) capillary deceleration in tandem with (iii) diffusion limited freezing.
Particular morphology of structures depends on absorbed fluence and number of pulses.
Formation of the structures is usually attributed to plasmon activity, which leads to the LIPSS (laser induced periodic surface structures, ripples).
On our opinion, plasmons only dominate in the interplay if absorbed fluences are small and the multiple repetition regime is used.
Indeed, the chaotic (not ripples) structures are produced by X-ray pulse where plasmon excitation is not possible.
Therefore the wavelength should be added into the list of parameters governing the final morphology of an irradiated surface.
It was shown that for the small number of pulses, either large fluences or short wavelength the chaotic structures different from ripples are formed.
Another important governing parameters are connected with geometrical limitations.
They are a radius of a focal spot on an irradiated surface and thickness of a film.
Indeed, surface structures have the finite lateral sizes (submicron scales).
Therefore for tightly focused optical light pulses, when diameter of a focal spot is smaller than lateral spatial scales, definitely will influences the surface structures.
Those problems are analyzed in the report.
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