A Dichroic Beamsplitter for the Laser Protection of Infrared Detectors

Round 1

Reviewer 1 Report

Thin-film elements are one of the main attributes of modern laser technology. In turn, the emergence and development of new laser devices requires the development of technology for thin-film products, the search for new materials, and the study of their optical properties. Therefore, the publication of new materials on this topic is quite logical. The presented work solves the problem of optimal separation of two optical channels: power, laser on YAG:Nd and its second harmonic channel, and research, measuring in the IR region ( 3.6-4.7 μm) one. The problem was solved using new coating materials that provide high optical stability (laser channel) and relatively high channel separation. In general, the work corresponds to the theme of the special issue “Research on Infrared and Laser Thin Films” of the journal Coatings. May be published after appropriate revision. Remarks 1. The separating silicon wafer with thin-film coatings is located at an angle of 45° to the measured beams. The reflection coefficients s and p polarizations must be different. This is not reflected in the work. What is "average polarization at the angle of incidence of 45°" ? 2. In this work, the channel separation factor ~ 0.005 was obtained (what is with the transmission in the power channel, which depends on the polarization ?). It would seem that this is good. But the paper claims possible laser power densities greater than 3 GW/cm2 . Those a spurious laser beam with a power density of up to and more than 15 MW/cm2 can pass into the measuring channel, which can be dangerous for the measuring channel. Please clarify the limitations. 3. The work is focused on the military use of the results. However, there is no doubt that similar tasks exist in completely “peaceful” areas: medicine, security, for example ecological, science. Medical applications are no less important than military ones. Can you generalize the results?

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Reviewer 2 Report

It would be much more interesting if the authors discussed in more detail:

1)      „…high transmittance in the MIR region (3.6-4.7 µm) at the angle of incidence 74 (AOI) of 45°”                                                                                      line 74

 2)      “…(?) denotes the average polarization at the angle of incidence of 45°, and {Δ1,? }, {Δ2,? }, and {Δ3,? } are design tolerances in the corresponding wavelength ranges”                                                                                                                                                                   line 110-111

 

3)      “An Optorun Electron-beam deposition plant was used for the fabrication of the dichroic beamsplitters, which were deposited on monocrystalline silicon substrates (Φ25.4×3.2 mm) by IAD at 250 ℃ with a base pressure of 2.4×10⁻⁴ Pa.”                                                                                                                                                                                                                        line 140-142

 

I find this article interesting and will recommend it for publication.

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Reviewer 3 Report

The current article aims to develop and characterize a Ta₂O₅/SiO₂ multilayer system using ion-assisted electron-beam deposition, with applicability in dichroic beamsplitters for infrared detectors. The topic of this manuscript is actual and interesting, it presents great scientific importance, and the paper is well-structured, though there are a few issues that need to be addressed towards the improvement of this work before publication.

Some observations are summarized below:

1.      Please carefully proof-read spell check to eliminate grammatical and spelling errors like: line 194: It can be observd…

2.      The novelty of the study is not clear. There are several scientific articles in the literature (as well as companies) that present same materials/coatings systems for laser applications: ex: Wang, Y.; Cheng, X.; Shao, J.; Zheng, C.; Chen, A.; Zhang, L. The Damage Threshold of Multilayer Film Induced by Femtosecond and Picosecond Laser Pulses. Coatings 2022, 12, 251. https://doi.org/10.3390/coatings12020251, or Deng, X.; Su, J. Laser Protection Properties of Multi-Band Non-Regularized Highly Reflective Films. Coatings 2022, 12, 1614. https://doi.org/10.3390/coatings12111614

3.      How many samples were produced and characterized in the current study?

4.      The captions of the figures should provide more details regarding the analyzed sample to avoid confusion. Some of them contain only the word sample: ex: sample images…; damage morphology of the samples…, and so on.

5.      Which is the total thickness of the multilayer system? Does this aspect affect the spectral characteristics? A schematic representation of the structure of the sample should provide a clear idea.

6.      Please describe in detail the durability and environmental tests performed on the developed samples. Are the performed tests according to some standards?

 

Author Response

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