Variation in Electron Radiation Properties Under the Action of Chirped Pulses in Nonlinear Thomson Scattering
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper by Youwei Tian et al. is devoted to the theoretical study of the dynamics of electron motion and the properties of radiation emission during the interaction of electrons with relativistic chirped laser pulses in the approximation of nonlinear Thomson scattering. The authors numerically (on the basis of the standard fourth order Runge-Kutta method) solve the system of Lorentz equation and energy equation to determine and describe the motion state of the electron in the intense laser Gaussian pulse. Detailed attention is paid to the study of changes in the state of electron motion and the distribution of radiation emission depending on the characteristics of the chirped laser pulses. The influence of the pulse width on the chirp parameters is investigated. The authors established a complex effect of the chirp parameters and pulse width on the electron trajectory and radiation characteristics. In particular, the electron interacting with the Gaussian circularly polarized chirped laser pulse first makes a spiral motion similar to an isogonal spiral. After adding the chirp parameter, the range of the electron's trajectory changes greatly… The main effect of the chirp on the emission is that the pulse frequency changes with time. For example, when the pulse width is 2𝜆0, 4𝜆0, 6𝜆0, the trajectory becomes more continuous and regular after adding a small chirp parameter. With the increase of the pulse width, the radial compression effect of the chirp becomes more obvious. It should also be mentioned that the effect of morphometric transformation of the emission distribution becomes more obvious under the influence of the chirped pulse. The peak value of the electron emission energy increases with the increase of the absolute value of the chirped parameter. The change in the emission energy distribution in the time dimension is also observed.
The paper by Youwei Tian et al. has the scientific merits, is of a theoretical and practical importance, however, there are some critical points to be clarified in order to meet the possible questions of readers:
i). Authors should take into account that readers will immediately have questions about both the abstract and the conclusion of the article. Namely, what is the essence and novelty of the method they proposed? The abstract, conclusion, and final part of the introduction are written in general terms without a specific indication of the essence and concrete novelty of the author's approach and results. It is worth to add a few concrete results.
ii). In the introduction, the authors have presented the detailed review of the known papers devoted to interaction of atomics systems (electron ensembles) with the chirped laser pulses, including ionization dynamics of atoms, high-order harmonic generation etc. It is worth to add some known papers on direct numerical study of electron dynamics and radiation emission with relativistic chirped laser pulses in the nonlinear Thomson scattering (for example, look the additional refs below to be added)
iii). In section 2 the authors present the master equations of their model. The Eqs, (7-10) should be checked.
iii). In Section 3, the authors present their main results of the electrons motion analysis, Spatial distribution of radiationб time and frequency spectra analysis... It might be useful for readers to note the directions of the Poynting vector S plus the corresponding contour lines (S/S0= const) in Figures 2, which show the trajectories of an electron with different pulse widths at different chirp parameters.
iv). The authors considered the Gaussian circularly polarized laser chirped pulse, which can actually be considered in a certain sense as “chaotic light” compared, say, to a similar single-mode Lorentz pulse. Accordingly, in the process of interaction with electrons, the photon correlation and multimode effects can play a definite role. It would be interesting for readers to at least briefly comment on the possible manifestation of the above-mentioned effects in the dynamics of electrons and radiation characteristics...
v) In order to take into account possible questions from readers, it makes sense to expand the list of references and add links to well-known monographs and articles that discuss in detail the issues of study of electron dynamics and radiation emission with relativistic chirped laser pulses in the nonlinear Thomson scattering as well as the stochastic properties of the gauss laser pulses etc. . Possible Refs. can be added as follows: 1) J. Koga, T. Zh. Esirkepov, and S. V. Bulanov, Nonlinear Thomson scattering in the strong radiation damping regime. Phys. Plasmas 12, 093106 (2005); https://doi.org/10.1063/1.2013067 2). K. Lee, S.-Y. Chung, and D.-E. Kim, Relativistic Nonlinear Thomson Scattering: Toward Intense Attosecond Pulse. In: Advances in Solid State Lasers Development and Applications, Mikhail Grishin (Ed.) (InTech, 2010), ISBN: 978-953-7619-80-0, DOI:10.5772/7964; 3). A.V. Glushkov, Glushkov A.V., Multiphoton spectroscopy of atoms and nuclei in a laser field: relativistic energy approach and radiation atomic lines moments method. Advances in Quantum Chemistry (Elsevier). 78, 253-285 (20190; https://doi.org/10.1016/bs.aiq.2018.06.004; and others (at the discretion of the authors);
vi). Some editorial corrections are needed. For example, a) Page 2, lines 75-77; “ This paper is based on cross parameter direction. This paper is based on cross parameter direction. Based on the research of Kumar et al. [27], The characteristic parameters of pulse width and chirp are selected for cross analysis”??? b) Please, correct the phrase (page 3, line 98): ” the solution to Helmholtz's equation 𝑨”… c) Page 5, lines 167-168; “On the basis of classical electrodynamics, we use the fourth-order Runge-Kutta algo rithm to solve the partial differential equations of the equation”??? etc;
vii). Please, the authors should ensure that all abbreviatures, all quantities (parameters) in the figures and formulas in the corresponding schemes are defined and explained.
Recommendation: The paper by Youwei Tian et al has the scientific merits, is of a theoretical and practical importance. This paper can be recommended for publication in the journal "Applied Sciences" (MDPI), provided that the authors comply with the points, listed above.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper considers nonlinear Thomson scattering of chirped laser pulses. The topic is relevant to intense laser physics and the paper contains interesting numerical results. In my opinion, it could be accepted for publication, after some revision.
Here are my main comments:
- On pages 3-4, the writing of equations (5) to (10) is not appropriate. The authors could easily define auxiliary functions, eventually given in appendix, that would allow the writing of these equations in a more compact form.
- On line 107, intensity units are missing.
- Eq. (14) should be corrected.
- On section 3, the numerical results are quite interesting, but deserve a more quantitative and convincing analysis. The present discussion is too long and too vague. The authors should give a more clear physical interpretation of their main results.
- The English writing is not good, and I give a few examples: On line 59, the expression “chirped laser pulse analysis” appears twice on the same sentence; on line 85, R^1 should be corrected, on the same line ‘te' appears instead of ’t_e'; on line 155, the expression “Movement trajectory” is inappropriate, and so on. The authors should carefully revise the paper.
- Furthermore, on line 108 "vertical" and "horizontal distances" seem to refer to parallel and perpendicular directions with respect to laser propagation. This should be changed.
Comments on the Quality of English Language
The English writing is not good. The authors should carefully revise their paper.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe subject and objectives of the manuscript are clearly explained in the abstract. However, as the manuscript contains some figures with a large number of small subfigures, it is very hard to follow the interpretation of the results. The authors need to find a solution allowing to show the major results as figures with acceptable size and allowing simple interpretations. May be the number of subfigures can be largely reduced. The manuscript contains very long paragraphs in which there are some repetitions and this does not help the reader to catch the message of the authors. I think a shortened new version of the manuscript keeping the major points will be very interesting for the readers.
In addition to this general comments, I propose to tackle the following issues:
- The title mentions nonlinear Thomson Scattering but this is not considered in the manuscript if I am not wrong.
- In page 2, the sentence "This paper mainly focuses on this content". It is not clear what is meant by this sentence and why do to the authors focus on this ?
- "cross parameter direction". I think one can use the term "combined effect of chirp parameter and pulse width" or something similar to this.
- Check R' in line 86. Indicate that you are using a spherical coordinate system.
- Check line 87.
- In page 3, it is not indicated that the propagation is in the z-direction.
- In line 106, the unit of a_0 is not indicated.
- In line 108, I think "t" should be replace by "ct" where c is the speed of light.
- In eqs 5-10, why one stops at power 4 of epsilon for Ex and Ey components while going to power 5 of epsilon for Ez component?
- Can you give a ref for these eqs?
- Line 149, can give a ref for the RKF method?
- In page 5, it is not clear what symbol is used for the waist z or b_0?
- In the same page, what does I stand for?
- In line 160, the zero superscript should be a subscript.
- In line 165, replace "will not change" by "are kept constant".
- Line 168 check this sentence.
- Line 169, the number of the figure is not indicated.
- Line 178. "Comments are ..." It is not clear, must be rephrased.
- Lines 197-198 to check.
- Line 203, "at the moment" what is meant by this?
- Line 210. there is a repetition.
- Line 223. I cannot understand where are the experimental results.
- The conclusion seems to be short. It can be developed with also the perspectives and future possibilities and applications of the presented results.
- Ref [1] and ref [20] are identical
The English is correct but the paragraphs are long and do not allow to extract easily the main messages and results.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this revised version of the manuscript, the authors have taken into account my comments, and improved the quality of their work. In my opinion, the paper can be accepted for publication in the present form.
Author Response
Sincerely thank you again for your careful review and valuable comments. Your suggestions have made our paper more rigorous and reasonable. We truly appreciate your work!
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors did answer all the questions and the comments raised in my previous report. The changes which they have made in the revised version of the manuscript have clarified many points and imroved its quality. The only point which has not been considered concerns the size and quality of figures. In my first report I have mentioned the possibilty to reduce the number of subfigures in some figures by maintining only subfigures with the major results. The other possibilty is to split the figures. Except this point, the only point which remains unclear for me concerns line 100 for time t_e=t-R'+n.j.
As t_e and t represent times and R' and n.j represent lengths, they cannot be added unless the velocity is equal to 1. I understand the all physcial variables are normalized by 1/k_0 and 1/omega_0 but still I don't see. Please provide an explanation for this or correct it. By the way, in line 103 don't usr capital A in polar and azimuthal angles.
Author Response
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Author Response File: 
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