Femtosecond Laser-Induced Evolution of Surface Micro-Structure in Depth Direction of Nickel-Based Alloy
Round 1
Reviewer 1 Report
The authors present a combined experimental/theoretical study on femtosecond surface structuring of a Nickel alloy. While the introduction and the experimental section are clearly written, the simulation and discussion section are somewhat confusing and unclear. The modeling section aims to describe the evolution of microholes but does not tackle their initial formation. Clearly, they evolve due to the surface roughness induced by the initial scans but this does not seem to be reflected by the model. How do the assumptions of initial surface inhomogeneity (which are required to seed microhole formation) influence the formed microholes? A clear comparison between experimental observations and the corresponding simulation are insufficient. I would like to comment on some points in more detail:
Line 15f: Scan speed and focal position are not processes, rather processing parameters.
Line 97ff/line 109ff: Equation 1 defines n as the pulse-to-pulse overlap within a scan along the x-direction. However, the lines just before figure 1 seem to redefine n as the number of runs of the scan program.
Line 121ff: What is the time between two scan lines? What is the time between two passes of the scan program?
Lines 152f: The two-temperature model is only concerned with heat transfer and does not include a description of ablation.
Equation 5: Is it relevant to include the change of the beam radius with depth on the length scale of the ballistic electron transport (some 10 nm)? I would presume that this term can easily be neglected, simplifying the model.
Equation 7: This suggests M^2 = 1. Is this truly the case? If so, Lr ~ 305 µm follows.
Lines 175ff: How are the enthalpies of fusion and vaporization considered?
Table 1: Where are these parameters taken from?
Figure 1a: Fluences in the Petajoule per cm^2 region seem excessive.
Lines 218f: The text above does not provide enough information to interpret table 3. The initial depth of what and which absolute distance are listed herein?
Lines 238f: Why is the pulse energy reduced out of focus? Where is the energy transferred to? The referenced equation 6 only suggests an increase in spot size.
Figure 5a: Again, Petajoules per cm^2 seem excessive.
Lines 279f: What is ‘smart drying’?
While I consider the manuscript somewhat interesting, I see the need for significant improvements in clarity prior to publication.
Author Response
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Reviewer 2 Report
This paper presents a study on the fabrication of surface microstructures in depth direction of nickel-based alloy by femtosecond laser processing.
I found some merits in this paper to be published in the journal. So I recommend it for publication.
Author Response
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Reviewer 3 Report
In this article, authors performed micro-structuring of nickel-based alloy (DD15) with femtosecond pulses at different energies, defocusing amount of beam and scanning speeds. Authors also performed the theoretical studies to support the experimentally obtained microstructures resulted through the two-temperature to accurately attribute the process.
The work performed by the authors is well-organized and the quality meets the standard of the journal. The manuscript is well written and have little to no grammatical mistakes. Considering these, in my opinion, the work reported in the present form can be accepted for publication with minor comments.
Comments:
1. Abstract: line 15: what is the “law” that authors were referring to? Please indicate it here or else remove the word.
2. Line 48: Authors can modify the sentence “widely used because it is not limited by the shape of the target material and other properties” to “widely used because of their several applications such as in wettability, friction resistant and trace level explosive sensing [1].”
3. Line 78: “Nonetheless, in the two-temperature model, formulas such as for the spatial distribution of laser energy provide a better theoretical basis for establishing the relationship between laser energy and the location of the material surface in space, achieving the prediction of the evolution pattern of micro-structures in the depth direction, and then obtain various different roughness values, bringing more possibilities for the properties testing of TBCs.” Split this sentence. It would be too hard to follow.
4. Line 96-97: Authors mentioned that laser beam was moved using galvanometers. And further also mentioned that the stages were moved at 500 mm/s. Did they do simultaneously or independently in different experiments? Please explain?
5. Is the stage speed 500 mm/s or is it a typo? Please explain. The area scanned looks to be 1 mm * 1 mm i.e., 1 mm2. Does this high velocity require? List a table depicting the number of pulses would interact at certain speed of the stage, repetition rate of laser and beam diameter at the nickel’s surface (in addition to just giving formula).
6. How authors optimized the “40 μm along the y-direction”? Please show any optimization studies.
7. Figure 4: Authors are advised to make a table on the fluences estimated at each energy.
8. Line 265-268: Is it the case at all fluences and peak energies. Authors recommended to make a specific statement describing the exact observation made in ref 25. Authors also could also include the following reference [2] for the interests of reader.
1. M. Sree Satya Bharati, S. Abdul Kalam, B. Chandu, S. Hamad, and S. Venugopal Rao, "Instantaneous trace detection of nitro-explosives and mixtures with nanotextured silicon decorated with Ag–Au alloy nanoparticles using the SERS technique," Anal. Chim. Acta 1101, 157–168 (2020).
2. S. S. Harilal, J. R. Freeman, and P. K. Diwakar, "Femtosecond laser ablation: Fundamentals and Applications," in Laser Induced Breakdown Spectroscopy: Theory and Applications, S. Musazzi and U. Perini, eds. (Springer Berlin Heidelberg, 2014), pp. 143–166.
Author Response
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Round 2
Reviewer 1 Report
The authors addressed most of my concerns. However, I do not see the issue raised in point 10 as resolved:
In equations 5 and 8, the energy source term S (units of energy per volume) and the fluence F (energy per area) are defined. However, table 1 uses S as “peak fluence at focal plane” and F as “repetition rate”.
In line 101, phi is defined as the beam diameter. However, equation 8 suggests that phi is the beam radius. I suggests to consistently stick to either beam radius or beam diameter throughout the manuscript instead of switching between the two.
I am still unable to corroborate the reported fluence values. Taking for example the pulse energies E and beam waist phi0 from table 1 and inserting them in equation 8, I get 51, 64, and 76 J cm^-2 which corresponds to the very unorthodox representation of 5.1*10^9, 6.4+10^9, and 7.6*10^9 J (100 m)^-2.
Lastly, the authors replied to my original point 10 with “This involves only errors of order of magnitude and has no impact on the subsequent simulations and discussions.”. How can deviations of the order of 10^12 have no influence on the result? Such fluences should result in instant vaporization of the entire simulation volume with the first laser pulse. This raises strong doubts about the validity of the model if an error of some 12 orders of magnitude do not impact the result whatsoever.
I encourage the authors to double and triple check the simulations and to remove ambiguities (such as unclear definitions of symbols, beam radius vs. waist, etc.) prior to a resubmission.
Author Response
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Round 3
Reviewer 1 Report
With the changes made by the authors, I consider the manuscript suitable for publication.
Please double-check the y-axis of figure 5a - I cannot validate it as the resolution is too low to discern the numbers.
