Modification of Diamond Surface by Femtosecond Laser Pulses
Round 1
Reviewer 1 Report
This article outlines the laser diamond interactions. It is very well written. Below are a few comments:
- What does “20C ÷ 600C” in line 142 mean? Similarly, please explain “∼ 10−4 ÷ 1 nm/pulse.” in line 461.
- Grammar: “it noteworthy” in line 424 should be “ it is noteworthy”.
- This article describes the experiments very well. Hand waving explanations were given for most experiments; however, more detailed theories would be very helpful.
- Grammar: “it noteworthy” in line 424 should be “ it is noteworthy”.
Author Response
ID: photonics-2571317
Title: Modification of diamond surface by femtosecond radiation
# Reviewer #1
%% Q1. What does “20C ÷ 600C” in line 142 mean? Similarly, please explain “∼ 10−4 ÷ 1 nm/pulse.” in line 461.
A1. Both are corrected. Now "...varied in the range from 20◦C to 600◦C."
and "...nanodroplets on the diamond surface grow at a rate ranged from ∼10^−4 nm/pulse to ∼1 nm/pulse"
%% Q2. Grammar: “it noteworthy” in line 424 should be “ it is noteworthy”.
A2. It is fixed.
%% Q3. This article describes the experiments very well. Hand waving explanations were given for most experiments; however, more detailed theories would be very helpful.
A3. Thank you for the high assessment of the experimental part of our work. As for the theory, we are afraid that the simple models described in the manuscript are all we have now (to the best of our knowledge). And this is not as little as it seems. In any case, the problem of laser-induced nanomodification of covalent crystals still awaits a deep theory.
Reviewer 2 Report
The article discusses the process of modification of diamond surface by ultrashort laser impulses. In the article such processes as multipulse evaporative ablation and surface graphitization are also discussed. It is postulated that graphitization is a thermally stimulated process that gradually develops over time. Laser graphitization occurs when the laser fluence exceeds a certain threshold, leading to three regimes of diamond ablation: surface graphitization, saturation of graphitization front penetration, and bulk graphitization. It is also demonstrated that the crystalline perfection of the graphitized phase depends on the orientation of the irradiated diamond face. Moreover, the author shows, that nanoablative etching occurs when the laser energy decreases below the graphitization threshold and laser processing can modify the diamond structure at the nanoscale and atomic level, creating nitrogen-vacancy complexes.
The topic discussed in the article is relevant and interesting for a wide range of readers. The article comprehensively describes the process of laser interaction with diamonds from laser-plasma formation to graphitization. The article is well-organized, the applied methods are adequately described. From the physical point of view I have only one specific comment:
I) Is the Drude model could be applied for the description of the laser-induced plasma? Which assumptions are applied in the model?
However, there are several issues that should be fixed before publications:
1) The laser pulse energies should be added to Table 1.
2) In the labels of the Figures the used laser should be specified.\
3) The error bars should be added to Fig. 2,4,6,9,10,13,14,15.
4) Perhaps the Fig.1b should be redrawn as a color map similar to Fig.12.
In conclusion, the following paper could be published in Photonics after minor revision.
Author Response
ID: photonics-2571317
Title: Modification of diamond surface by femtosecond radiation
# Reviewer #2
%% Q1. From the physical point of view I have only one specific comment: Is the Drude model could be applied for the description of the laser-induced plasma? Which assumptions are applied in the model?
A1. Of course, Drude is applied to laser-induced plasma. The estimation of the carrier number from the permittivity of the laser-excited solid medium was first made by Guizard et.al [1]. We would say that Drude's description of the laser-induced plasma is much more correct than that of a metal plasma. First, the laser-induced plasma produced without material destruction is relatively rarefied - less than 10^21 cm-3. This can be deduced from the absorbed energy, i.e. from the energy conservation. Drude supports this estimation. In the rarefied electron gas, electron-electron and electron-ion "collisions", which are ignored by the Drude model, are obviously less important. Second, the electrons in the laser plasma are relatively hot, and this again is good for Drude, since the assumed Maxwell-Boltzmann statistics are more plausible in this case. Note also that the first obstacle is more important because the main assumption we used to calculate the optical permittivity of the plasma is the independent electron approximation, which, as mentioned, works well.
[1] S. Guizard, P. D’Oliveira, P. Daguzan, and P. Martin. Time-resolved studies of carriers dynamics in wide band gap materials. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 116(1-4):43–48, 1996.
%% Q2. The laser pulse energies should be added to Table 1.
A2. Done
%% Q3. In the labels of the Figures the used laser should be specified.\
A3. Done in Figure 2,6,9,11,13,16,17
%% Q4. The error bars should be added to Fig. 2,4,6,9,10,13,14,15.
A4. It is not that simple. The stochastic experimental error that we can control and estimate is quite small in all these data. The depth was measured with a WLI profilometer (~0.5 nm error), the laser energy jitter was about 3%, the temperature measurement error was also less than 3%, etc. Of course, we cannot guarantee that the systematic error has been avoided, but we cannot estimate it either. Let us assume that we believe that the errors are small, less than the dots (symbols on the graph), and we add this remark to each figure you point to. "Estimated error is less than the size of the point".
It should be emphasized that the variations of the data you see in the plots are not experimental errors, but result from the fluctuations of the processes studied (etching, ablation, ionization, etc.).
%% Q5. Perhaps the Fig.1b should be redrawn as a color map similar to Fig.12.
A5. Unfortunately, we have no any idea how to to this. The value in images is some brightness, which is a complex function of refractive index, and even if we put some color scale, it will give nothing for clarity.
Reviewer 3 Report
This work summarizes the current research status about surface modification of synthetic diamond using ultrafast lasers, with an emphasis on femtosecond laser. Fundamental mechanism and major working regimes are covered, with the hard core knowledge well presented in an organized manner. The review has a potential to serve as a good summary to refer to about this field, as well as a solid reference for future research. Therefore I recommend acceptance of the manuscript for publication. Meanwhile, I would suggest some slight modifications to the manuscript to make it more accurate and more understandable to more general science readers:
- In the title, it makes more sense to use "femtosecond laser". instead of "femtosecond radiation", since, just like the author use in line 5, those lasers are the tools always used, and deserves a correct name in the title.
- In the abstract, between line 10-14, the author highlights the possibility of using fs laser to induce detects of NV in synthetic diamond, while a simple one sentence is indeed needed to exemplify why is it important. Although, the author describe in detail in section 3.8 of the benefit of such structural defects for quantum optics, probing and other fields, it's necessary to briefly highlight such reason in the abstract.
- In the introduction, starting line 41, the author mentions the diamond ablation is similar to metal ablation, while the author also mentions the diamond ablation has unique feature of graphitization. Can the author explain a little bit more the metal ablation, and its similarity to the diamond ablation?
-In line 61, very nice talking about the potential of diamond as new active quantum devices with unique characteristics. It will be more sound to exemplify in a few words about the "unique characteristics".
- In line 94-95, what is the typical lattice response time? And what's that for synthetic diamond?
- In line 96- 97, the last sentence for the paragraph, it's more proper to replace "fast" with "ultrafast", and mention what specific processings those ultrafast lasers can do.
- In line 104, what is the definition of roughness, and what does the subscript a mean in "Ra"?
-Line 110: "other sources of radiations" are also lasers, so it's more proper to say "Different fast lasers were used to study ..."
- Line 122-123: Instead of using "fundamental harmonic", it's more commonly to use the"fundamental" or the "fundamental frequency"
- Line 126: what is a projection scheme?
- Line 229-233: maybe I missed somewhere, but is there a reference to cite for the equation used for e yield from muptiphoton ionization?
- Line 273-274: Add "primary" before "depending on".
- Line 23: "The only weak point" sounds too strong in general, and particularly for an ongoing research, therefor, I would suggest something like "One major weak point ...".
- In line 30, the author mentioned the two stages for the the interest in synthetic diamond, while the 2nd stage mentioned in line 55 needs to be "marked" more obviously as an "2nd stage".
- Line 38: add processing methods to after "One of the most effective".
- Line 41: is "similar to" more suitable than "typical for"?
- Line 77: add "and" before "if they even"
- Line 120: "Ti:Sapp laser modelocked laser" needs corrected to "Ti:Sapphire mode locked laser"
- Line 124: Does the author mean β-BBO (beta-BaB2O4) when saying " b-BaB2O4 (BBO)"?
- Line 274: typo when writing "~"
- Line 461: typo when writing "~"
- Line 517, 519, 577, 622, 682: typo when writing "~" and celsus degree
- I believe the the authors and the editors will work on the typos in the references,
Author Response
ID: photonics-2571317
Title: Modification of diamond surface by femtosecond radiation
# Reviewer #3
%% Q1. In the title, it makes more sense to use "femtosecond laser". instead of "femtosecond radiation", since, just like the author use in line 5, those lasers are the tools always used, and deserves a correct name in the title.
A1. I agree. The new title:
Modification of diamond surface by femtosecond laser pulses
%% Q2. In the abstract, between line 10-14, the author highlights the possibility of using fs laser to induce detects of NV in synthetic diamond, while a simple one sentence is indeed needed to exemplify why is it important. Although, the author describe in detail in section 3.8 of the benefit of such structural defects for quantum optics, probing and other fields, it's necessary to briefly highlight such reason in the abstract.
A2. I agree. Additional sentence is:
"Such defects have been at the forefront of solid-state physics for the past thirty years due to continuous attempts to exploit their unique properties in quantum optics, quantum computing, magnetometry, probing, and other fields."
%% Q3. In the introduction, starting line 41, the author mentions the diamond ablation is similar to metal ablation, while the author also mentions the diamond ablation has unique feature of graphitization. Can the author explain a little bit more the metal ablation, and its similarity to the diamond ablation?
A3. I restated this point. Now it sounds like:
"These applications, as well as many others, require suitable tools for diamond processing at the macro and micro level. One of the most effective is considered to be ablation, a traditional method of local laser exposure based on pulsed heating and vaporization of the surface layer of the target. The material removal rate achieved during diamond ablation is typical for metal ablation and, for example, in the case of nanosecond irradiation is hundreds of nanometers \cite{rothschild1986ki}. This similarity results from an inherent feature of diamond ablation - the intermediate graphitization of the diamond surface. Graphite-like surface layer, first discovered in 1960s \cite{bradley1965kd}, sharply increases optical absorption of originally transparent diamond. The absorption coefficient of graphitized diamond is $\sim 10^5$ cm$^{-1}$, which is close to the coefficient of metallic surface. "
%% Q4. In line 61, very nice talking about the potential of diamond as new active quantum devices with unique characteristics. It will be more sound to exemplify in a few words about the "unique characteristics".
A4. We add some speculations:
"...unique characteristics. To date, the NV center is one of the few objects that function as a well-controlled three-level quantum system. First, the quantization energy in the NV center significantly exceeds the energy of thermal fluctuations even at room temperature, so that the coherence time of the spin states can reach milliseconds \cite{balasubramanian2009fu}. Second, such a quantum system rigidly fixed in a solid-state matrix can in principle be scaled by creating an ordered array of individual NV centers. The bright luminescence of NV centers in combination with the high chemical and radiation resistance of diamond, as well as its lack of cytotoxicity, also make diamond attractive for technologies in the field of medical diagnostics and therapy."
%% Q5. In line 94-95, what is the typical lattice response time? And what's that for synthetic diamond?
A5. I add this in parentheses: "(1-10 ps)". I mean a very simple thing here - the time of energy transfer from the electrons to the lattice. Let's say the electron-phonon (electron-defect) collision time is about 1 fs and it takes about 1000 collisions to heat up the lattice. In this classical sense there is no difference between natural and synthetic diamond (both may contain impurities and structural defects, the phonon subsystem is of course identical).
%% Q6. In line 96- 97, the last sentence for the paragraph, it's more proper to replace "fast" with "ultrafast", and mention what specific processings those ultrafast lasers can do.
A6. It is replaced
%% Q7. In line 104, what is the definition of roughness, and what does the subscript a mean in "Ra"?
A7. This is the standard definition: arithmetic mean height, which indicates the average of the absolute height deviation along the sample surface. "a" means arithmetic.
%% Q8. Line 110: "other sources of radiations" are also lasers, so it's more proper to say "different fast lasers were used to study ..."
A8. I agree
%% Q9. Line 122-123: Instead of using "fundamental harmonic", it's more commonly to use the"fundamental" or the "fundamental frequency"
A9. Done
%% Q10. Line 126: what is a projection scheme?
A10. This is very common technique in laser physics and I have not described it in detail. In this scheme, the image of some shablon is projected onto the target surface. All wide field imaging is based on the projection scheme. In the context of material treatment, the litography technique is based on the projection scheme.
%% Q11. Line 229-233: maybe I missed somewhere, but is there a reference to cite for the equation used for e yield from muptiphoton ionization?
A11. I add the refference to original work.
%% Q12. Line 273-274: Add "primary" before "depending on".
A12. Done
Thank you for you efforts.
