Laser Induced Periodic Surface Structure (LIPSS) is produced by laser texturing of a sample surface. For this, a sample is to be scanned over a range with laser fluence nearby the ablation threshold of the particular sample. My query is if one sample is scanned and another is bombarded at one spot keeping the laser fluence and number of pulses constant, can I detect any change and can LIPSS be generated in both the cases?
See my paper from 1986, Excimer Laser Etching of Polymers in RG. So long as the fluence is the same, the surface effects will be the same especially for low fluences. With very high fluence nonlinear photothermal effects will dominate
The answer to your question depends on the spatial beam profile that you are using [I assume that you are using a pulsed laser system]:
Case 1: If you are using a beam profile there may be small differences between spot and scanning processing if you keep the number of pulses per spot (N) and the effective number of pulses (N_eff = number of pulses hitting the beam spot diameter) in scanning mode constant.
Case 2: If you are using a profile, there is a fundamental difference between both scenarios:
In case of spot processing, each irradiated surface location is hit by the same local fluence value that is varying across the radial beam position: F(r)_tot=N*F(r)
In case of scanning processing, a fixed surface location first "sees" rising fluences of the approaching laser beam, then is hit by the high fluence part of the beam profile, and finally is treated with the low fluence wing of the Gaussian fluence distribution. In other words, the fluence at a fixed location varies among the structuring process (in time) and often the high fluence part generates other surface structures (e.g. Spikes and Grooves) than the low fluence wing of the Gaussian distribution (LIPSS), i.e. close to the ablation threshold. As a consequence Spikes/Grooves may later be "overwritten" with LIPSS and then you are creating hierarchical micro-/nano surface structures upon scanning. These hierarchical (mixed) surface structures are then different from that of Case 1, where you can observe the different surface structures clearly spatially separated by their indivitual fluence ranges, i.e. the Spikes/Grooves/LIPSS are arranged in different annular structures arount the center of the irratiated spot location.
Let me add to my comment from August 16th 2020:
We have discussed this point in more detail in Section 4.4 of the (open access) review article
Article Maxwell Meets Marangoni—A Review of Theories on Laser‐Induce...
Thank you very much Prof. Bonse. It was so nice of you to help me with my queries.
Best Regards,
Rudrashish
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