Potential of Sub-THz-Wave Generation in Li2B4O7 Nonlinear Crystal at Room and Cryogenic Temperatures
, Snezhana Turgeneva 3,4, Nazar Nikolaev 5, Alexander Mamrashev 5, Sergei Mikerin 3, Fedor Minakov 5, Andrey Simanchuk 3, Valery Antsygin 5, Valery Svetlichnyi 2, Valery Losev 1 and Yury Andreev 1,2,6Round 1
Reviewer 1 Report
I have read the manuscript with interest. The authors present a solid work for the potential generation of THz radiation by pumping the LB4 crystal with a high-power laser at 800 and 1064 nm. The authors support its analysis by simulations, and the references are appropriate. Minor comments are listed below.
Reviewer Comments:
1.- In what kind of practical applications are used THz radiation? Mention it in the Introduction section.
2.- From Fig. 1A, how do the authors get values in wavelength above 5 microns measuring transmittance if the spectrophotometer spectral range is 190-3300 nm?
3.- Figure 1B and Table 1 show the absence of data for the wavelength of 636 and 846 nm. What is the factor that causes this absence?
4.- Line 133: it could be used parenthesis in “…coefficient with cooling (Figure 2A) is not as radical as…
5.- What was the software or code used to perform the simulation presented in Fig. 3?
6.- The manuscript is well written, clear and formal, so that a contraction like let's can be avoided.
Author Response
Point 1: In what kind of practical applications are used THz radiation? Mention it in the Introduction section.
Response 1:
According to the first comment, we decided to expand the introduction part with the following paragraph (lines 45-55):
There are several key applications of intense THz waves. Development of compact charged particle accelerators, the dimensions of which are limited by the wavelength of the accelerating electromagnetic field. Advancement of nonlinear optics into new spectral ranges and study of the selective effect of THz waves on living organisms. Moreover, there is a recently unsolved problem of designing and building THz Light Detection and Ranging (LiDAR) system which demands a high-power terahertz source. Since many hazardous industrial and greenhouse gases have absorption lines at sub-terahertz frequencies, where the atmospheric transparency windows are located, such a LiDAR allows monitoring of its small components in the surface layer at kilometers distances for environmental and climatic purposes.
Point 2: From Fig. 1A, how do the authors get values in wavelength above 5 microns measuring transmittance if the spectrophotometer spectral range is 190-3300 nm?
Response 2:
This graph combines measurements from two spectrometers Cary 5000 (0.19-3.3 µm) and FT-801 (2.5‑25 µm) (see methods).
Point 3: Figure 1B and Table 1 show the absence of data for the wavelength of 636 and 846 nm. What is the factor that causes this absence?
Response 3:
The optical axis lies in the plane of our samples. In this case, the measurement for an ordinary wave is an easier task, since the p-polarization will be orthogonal to the optical axis for any orientation of the sample pressed against the prism in the Metricon system. In the case of the s-polarization, the measurement accuracy begins to depend on the accuracy of the azimuthal position of the sample, which, requiring greater accuracy in positioning, so, it becomes quite time-consuming. Due to this fact, initially, we planned to measure only two extreme points of the range: 517 nm and 1550 nm to qualitatively assess the correspondence of ne of our samples with the reference data. However, due to the strong discrepancy in Burak's 1987 work, in the case of an ordinary wave, we additionally measured a wavelength of 1.3 μm.
In general, even three points show good agreement between our data and those known from the reference. However, if the reviewer insists - we can additionally measure the missing points, which, of course, will take some time.
Point 4: Line 133: it could be used parenthesis in “…coefficient with cooling (Figure 2A) is not as radical as…
Response 4: The text was corrected following the comment of the reviewer (lines 153-154).
Point 5: What was the software or code used to perform the simulation presented in Fig. 3?
Response 5:
We use the following python script that simply calculates L coherence from formula (4) for all possible nonlinear interactions: https://drive.google.com/file/d/1eF18_HOulezfmwmOcXMTeyfX3oEop8mC/view?usp=sharing
To calculate phase-matching curves we use scipy.optimize.root function according to the following script:
https://drive.google.com/file/d/1LJPQigy1qQXpDsbHdgwu4cJgSj1IfJtR/view?usp=sharing
Obtained data frames are then imported in Origin.
If it is necessary, we can add these scripts in supplementary, or in another way.
Point 6: The manuscript is well written, clear and formal, so that a contraction like let's can be avoided.
Response 6: We are grateful to the reviewer for a careful analysis of our work. The text was corrected following the comment (line 220).
Reviewer 2 Report
The optical properties of the LB4 crystals as well as their structural properties are well known. Therefore, in my opinion, the novelty, significance and scientific soundness of the presented results are low. However, the reviewed manuscript is not bad and can be published in Crystals after major revision. I leave the final decision to the Editor.
Author Response
Response 1: We disagree with the opinion that the significance of the manuscript is low. This work contains new knowledge such as measurements of THz properties of LB4 crystals at cryogenic temperature, careful calculation of possible three-wave interactions for collinear generation of terahertz radiation under different laser pumping. Therefore, we assume that for the terahertz community, the article carries novelty and significance. To highlight the significance of the results obtained, we have significantly revised the abstract of the manuscript (lines 20-32).
Reviewer 3 Report
The manuscript is another publication showing an application of Li2B4O7 crystals for UV, VIS and IR frequency-conversion including the fourth-harmonic generation of a Nd:YAG laser. The significant novelty lies in analysis of its spectroscopic properties at cryogenic temperature. Analyzing the content and presentation of the results, no significant irregularities were found, However, the abstract is little informative and should be improved to show the most important achievements.
Author Response
Response 1: According to the response, we decide to significantly revise the abstract to make it more informative and to highlight new results obtained. (lines 20-32).
Round 2
Reviewer 2 Report
The reviewed paper in its present form deserves to be published in Crystals.
