Properties of Holographic Elements Based on Periodic Structures in a Wide Range of Angles of Incidence

Round 1

Reviewer 1 Report

In this manuscript, the authors experimented to measure the diffraction efficiency (DE) by varying two rotation angles (yaw axis – alpha angle in the article, and pitch axis – beta angle in the article), to simulate the different incident angles of light. The obtained result is subsequently used to compare the year-round average DE with the trajectory data of local cities, with two different Holographic optical elements (HOE) orientations. The authors conclude that the overall DE of the HOE is higher in the case of using two angles. Here are some comments from the perspective of the reviewer:

First of all, I had to say the innovation of this manuscript is trivial, and the presented content is some like a test to grab a set of data for a specific application. It is straightforward to understand if someone considers the overall DE along the path in a 2D plane (two brag angles) could have a better result compares to the result by accumulating in a single line. It’s suggested to submit this manuscript to the journals that focusing the engineering applications, with the improvement in the following aspects:

• It’s suggested to consistence the range to the alpha angle from figure 2 to figure 5.
• In the two-angles rotating experiment, I am assuming you are rotating the beta angle first and fixed it, then rotating the alpha angle to record the data. Did you compensate for the alpha angle change due to the rotation in the pitch axis (beta angle)?
• Finding the best orientation at a certain sun trajectory is a 2D optimization problem. Compares to the path presented in the article, which uses a -8-degrees orientation. Did you consider establishing an optimization formula to finding the best orientation with the given sun trajectory? For example, using the least energy with the Gaussian-Newton method.
• In the aspect of engineering application, did you also consider the sunlight intensity change at different times and seasons? Also, since the sunlight covers all the visible light spectrum, but the result only considers the diffraction light for two lasers wavelength (633 nm and 442 nm). I am not sure what’s detailed application you are applying this HOE for, but you will also need to consider the absorption rate of the material.

Author Response

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Reviewer 2 Report

In general, the limitations of the proposed theory should be better explained. Also the validation of the data used for the analysis should be shown in the paper, how statistically representative is the data?

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Reviewer 3 Report

The manuscript presents interesting scientific findings but the presentation is poor and must be greatly improved.

1. The entire manuscript needs to be proof-read by a native English speaker.
2. It should be explained (with a figure) how the gratings were recorded, because the directions of the k-vectors of the interfering waves during recording define the direction of the planes formed in the grating. Additional figure should be provided for illustration of the 3D distribution of the reflecting planes in the gratings.
3. Fig. 1, all symbols must be explained in the figure caption. The direction of rotation should be shown using one arrow, indicated the positive angle of the rotation.
4. All axes in all figures should have arrows.
5. "Scheme 1 is traditional." should be replaced with "Scheme 1 (Fig. 1(a)) is conventionally used for ... [references]".
6. "The angle α of grating rotation around the Z axis is changed." Not clear what the authors are trying to say by "changed".
7. "The results presented below refer to structures obtained under optimal conditions:" It should be explained why these conditions are optimal? Is there some formula or was it found by just trying out?
8. "Scheme 1 diffraction efficiency measurements give the classical contour of angular selectivity shown in the Figure. 2." should be "Diffraction efficiency measured using Scheme1 demonstrates the conventional contour of angular selectivity as reported in previous literature [references], as shown in the Figure. 2."
9. Fig. 2 caption "according to scheme 1" should be "using Scheme 1" or "in Scheme 1".
10. Fig. 6, I strongly suggest to use more conventional presentation of such data as a 2D colored image, with x,y axes and the value along the third axis is represented by a color.
11. Fig. 7 Fonts are too small and cannot be read.

Author Response

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Reviewer 4 Report

This paper presents the results of an experimental study of the diffraction and selective properties of non-slanted volume gratings and hybrid structures in a wide range of angles of incidence in three-dimensional space are presented. This is interesting experimental work especially taking into account that holographic gratings are original systems that were created by the authors.

However, there is one, but serious note which authors must take into consideration:

The authors proposed to use this kind of holographic gratings for increasing the efficiency of photovoltaic systems. However, the practicability of this approach is not obvious. Firstly, it is no clarity from the text of the paper if the use of holographic gratings in this field is already established approach or it`s just an idea proposed by authors. Secondly, it is necessary to describe in more detail how exactly holographic gratings may be used for such purposes. In particular, authors have to explain for which kinds of photovoltaic systems (big-size thin-film solar modules or small-size solar cells) holographic gratings can be exploited.

To summarise: This research work is worth publication, but it needs some corrections.

Author Response

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Round 2

Reviewer 1 Report

Reviewer holds previous stands.

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