Upconversion Photonic Doppler Velocimetry Based on Stimulated Brillouin Scattering

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the manuscript, an optical up-conversion photonic Doppler velocimetry based on stimulated Brillouin scattering with all-fiber link structure is proposed. Although the use of SBS for measuring shock waves in photographic Doppler scattering has some novelty in application, the basic principle of this article has become common knowledge in the field of Brillouin scattering measurement. The main theoretical description of this manuscript can be found in published books. For example, Govind P. Agrawal, "Nonlinear Fiber Optics" 4th ed., 2007, Elsevier.

In addition, as shown in Figure 9 (mistakenly marked by the author as Figure 8), the velocity time histories measured by DLHV and SBS-PDV have small differences and cannot reflect the advantages of the proposed method in terms of measurement accuracy.

Considering the weak innovation of the manuscript and the unclear advantage of measurement results, it is not recommended to accept it.

Comments on the Quality of English Language

The English expression of this paper is good.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a scheme for implementing an upshifted heterodyne velocimetry based on stimulated Brillouin scattering. This scheme can realize the upshifted heterodyne measurement with only one laser beam, and can carry out long distance measurement. The content of the manuscript is novel and the results are persuasive. I have the following questions.

1, In Figure 5, the threshold power of SBS seems to have a sudden change process with the increase of laser power. What's the physical mechanism here? Is there some kind of phase transition involved here?

2, The efficiency of Brillouin scattering is very low, and the dissipation of the system will be increased if long distance detection is required. In this case, how to improve the efficiency of Brillouin scattering?

3, The acoustic wave frequency in the medium is about 11GHz, which is in the same band as the microwave. stimulated Brillouin scattering also has relevant research in the field of magnonic (spin wave quantum), such as magnon laser based on Brillouin light scattering, optomagnonic frequency combs generation based on magnon-induced Brillouin light scattering, etc., which  should be mentioned in the introduction section. In addition, can the scheme in the manuscript find relevant applications in spin wave detection?

Comments on the Quality of English Language

The language of the manuscript should be further polished.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The submitted work, titled "Up-conversion Photonic Doppler velocimetry based on stimulated Brillouin scattering" presents a new method for Doppler velocimetry that can be used to study shock waves. The work is interesting but it should be considered after major revisions, according to the comments below:

1) Abstract: What do the Authors mean in the abstract by “shifts down relative to the source light”? In terms of frequency or? The meaning of “laser interference structure” is also not clear at this point.

2) The total light field is obtained by superposition of SBS light and Doppler shifted light, but Brillouin scattering is also sometimes described in terms of Doppler effect. Do the Authors have some comment on this?

3) In Figure 1, why do the Authors use silicon dioxide as an example? How is this related with the studied specimens?

4) The section “Theoretical considerations” is too detailed for the Brillouin part, which is well known. However, this theoretical understanding has not been used to represent the obtained spectra so the reason to discuss it is not clear.

5) Figure 3: “Oscilloscope” (minor).

6) Minor language editing is necessary, for instance: “When detecting target is static relative to probe, the laser -> is <- directly reflected from surface back to probe into circulator.”

7) Are the results of Figure 8 an effect of Doppler or pressure?

Comments on the Quality of English Language

Minor editing of text and figures is required.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The author addressed all my doubts and I agreed to publish the manuscript in its current version.

Author Response

Thanks again to the reviewers for corrections.

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors made an effort to improve the manuscript and to consider all review comments. I believe that the article can be accepted and evaluated by the readers after considering some final comments.

Line 195: “The frequency of Brillouin scattering light at about 193.53765 THz is lower than the main laser by ~11 GHz.” The Authors should probably give some uncertainties here and write the numbers accordingly.  Is the frequency resolution better than 0.05 GHz?

Figure 5: How the Authors determine the positions of the peaks? The position of the peaks are given with 5 significant digits. Are the peaks fitted? Or is this the local maximum? What is the error bar? 

Comments on the Quality of English Language

Some minor polishing of language is still required, perhaps during proof reading. For instance, Line 193: “Therefore, the light from fiber laser and Brillouin scattering can be observes” -> “can be observed”.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf