Pump-Probe Detection of Diamond Ionization and Ablation Induced by Ultra-Fast Laser

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Article ID: 3504451

Title: Pump-probe Detection of Diamond Ionization and Ablation Induced by Ultra-fast Laser

Comments:

In this work, the authors utilized the pump-probe spectroscopy to detect the ablation of the ultrafast laser on the diamond. The ablation and ionization processes in the diamond were investigated and the experimental phenomenon was discussed under different ablation conditions. I suggest that it is a comprehensive work and it could be accepted after some major revision. First, the introduction of this work needs to be further improved, which is poorly logical, and needs to focus on the differences between this work and previous works, to emphasize the innovation and motivation of this research. For example, the authors discussed the graphitization of diamond as a key point, however, there is a lack of discussion of related work in the introduction. Secondly, the authors need to improve their logic when analyzing and discussing the experimental phenomenon. For instance, consider the discussion on the slow plasma decay (Line 282). Additionally, the analysis of the experimental results should be included in the abstract, not merely illustrating the phenomenon. There are also some minor revision should be made.

• Line 140, ... Figures 2b and 2c...
• Supplement the caption for the subfigure of Figure 6.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper uses the DFT, the Keldysh formula, and the finite element method for studying the critical plasma length of diamond. The pulse number, energy, and pulse width of laser pulses were varied in experiments to study and discuss the plasma length and the graphitization damage length inside diamond. This work is sufficiently adequate both theoretically and experimentally, well organized and suitable for publication in Photonics. Hence, I suggest that this paper be published after minor revision.

I have only one question, what standard is used to measure the performance of diamond? 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors studied the ablation of diamond samples by the focused ultrafast laser pulses both theoretically and experimentally. The free electron density in diamond after irradiation of pulses with different intensities was numerically simulated. Moreover, the electric field in diamond was also simulated at different laser parameters. In the experiments, the plasma morphology was characterized at different time delays by the pump-probe setup. Finally, the influences of pulse energy and width on the length of laser-written structures have been investigated.

 

The manuscript is well-written and organized. It aligns well with the requirements and scope of Photonics. Nevertheless, there are some issues that I believe the authors should address before publication.

 

Major issues:

• Materials and Method section. What are the dimensions of the diamond sample? I guess that the authors used a rectangular sample.
• The manufacturer and model information of the objective lens needs to be provided.
• In Fig. 4, the calculated density of free electrons is four orders of magnitude higher than the critical density. I can agree that the density could be slightly higher than the critical density, but four orders of magnitude seem too high. The self-focusing effect and graphitization in diamonds may reduce the absorption of light pulses, resulting a free electron density lower than your calculated value. Please comment on this issue.
• On line 239, you set the field power by the measured reflectance index of 0.72. However, the absorptance/reflectance of transparent materials depends on the intensity of the incident pulses [Phys. Rev. Lett. 102, 083001, (2009)]. You may revise your simulation or at least comment here.
• In Fig. 9, it is unclear why the length of laser-written structures decreased at pulse energy of 8 μJ.
• The error bar should be added in Fig. 8, 9 and 10.

Minor issues:

• In Fig. 4, compared to the term of “Power density”, the term of “Intensity” is a more commonly used term in the field of ultrafast laser processing.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I have reviewed the revised manuscript and the authors have made the point-to-point revisions according to my comments. Therefore, I can recommend the revised manuscript for publication in Photonics.