Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, the authors introduced oil-based refractive index matching fillers integrated with additive manufacturing components to suppress Fresnel reflection and improve optical system performance. The proposed method mitigates the aforementioned losses by applying various types of oil as fillers at the interconnections of optical components. The optical properties of 20 different vegetable oils, synthetic oils, and mineral oils were studied using terahertz time-domain spectroscopy (THz TDS). A multi-layer structure fabricated by fused deposition modeling (FDM) using highly transparent cyclic olefin copolymers (COC) in the THz radiation range was proposed. This highlights the implementation of oil-based index matching fillers and the potential application of the proposed method in imaging multi-layer objects or structures with internal stratification.

The work is very beautiful, but there are still some issues that need to be noted.

1. In the experimental section, for better visualization, it is recommended that the author supplement the corresponding experimental flowchart and optical path diagram.

The author needs to supplement the exploration of relevant physical mechanisms in the abstract.

2. In the abstract section, it is recommended that the author rewrite it. It should highlight what was done, how it was done, what conclusions were drawn, what physical mechanisms were involved, and ultimately what applications were made.
3. In Figure 2, the curves overlap together, it is recommended to make adjustments.
4. The author needs to provide quantitative descriptions as much as possible for the description of Figure 5.
5. What is the physical mechanism behind the appearance of three internal reflections in this article?
6. Regarding terahertz technology, some related authors need to mention that, Terahertz technology in intraoperative neurodiagnostics: A review; Progress on reconfigurable terahertz metasurface devices based on sulfide phase change materials; Ultrathin broadband terahertz metamaterial based on single-layer nested patterned graphene.
7. The language of the article needs further optimization.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors The paper investigates reduction of Fresnel reflection losses in terahertz (THz) optical systems through the use of refractive-index-matching oils. The authors study 20 oils (plant, mineral, synthetic) using THz time-domain spectroscopy, and then test their effectiveness in reducing reflection losses in multilayer 3D-printed structures made of COC.   A systematic comparison of multiple oils for THz optics is presented. The idea of using oils as index-matching fillers for multilayer structures is interesting and practically useful. The measurements are well explained, and the multilayer demonstration shows clear effects. The topic is original and quite relevant in the context of THz imaging. The study addresses a clear problem (parasitic reflections in multilayer THz optical setups) and provides quantitative results showing signal gain.   The work is promising and contains publishable material, but improvement in clarity, scientific depth, and contextualization is needed before it can be accepted.   In particular:   - The abstract is overly long; it should be more concise and quantitative. Some sentences could be tightened to improve readability and focus on key results. - The introduction does not sufficiently compare this work with prior studies on refractive-index matching in THz optics. Other methods are mentioned only briefly. The novelty claim needs stronger justification with a clearer literature gap. - Please, add other details about the fabrication of the multilayer design via FDM technology. - The chemical/physical stability of oils (e.g., evaporation, degradation, temperature dependence) is not addressed. This is critical for practical adoption. - Table 2 could mention the statistical significance or measurement error for the signal gain. - The number of independent measurements, uncertainties, and repeatability tests are missing. - Equations (1–2): Variables need better explanation. - Figures 5(a)-(b) present unexpected vertical lines. Please, remove them. - The discussion could explore broader implications, such as scalability to larger systems or limitations for high-power THz sources.   Finally, this experimental paper is suitable for Applied Sciences. With revisions to improve clarity, conciseness, and contextual discussion, it could make a valuable contribution to the field of THz optical engineering.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept in present form

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have provided satisfactory responses to my comments. I would like to recomment the manuscript for publication.