Effects of the Processing Technology of CVD-ZnSe, Cr²⁺:ZnSe, and Fe²⁺:ZnSe Polycrystalline Optical Elements on the Damage Threshold Induced by a Repetitively Pulsed Laser at 2.1 µm

Round 1

Reviewer 1 Report

1) How the hydrogen escapes?

2) Operational regime; it is not clear.

3) Describe the hot isostatic pressing.

4) How the beam diameter changes?

5) How the collaboration is retarded with oxygen?

Author Response

Question 1) How the hydrogen escapes?

Answer: CVD-ZnSe production is carried out in a flow reactor over several weeks. Hydrogen and carrier gas are continuously extracted by a vacuum pump.

In the text:

ZnSe is deposited onto the substrate, and hydrogen is continuously pumped out of the reaction zone together with the carrier gas.

Question 2) Operational regime; it is not clear.

Answer: We are not sure which operational regime is mentioned in the comment. The testing Ho:YAG laser operated in the repetitively-pulsed mode, which is mentioned multiple times throughout the text.

Question 3) Describe the hot isostatic pressing.

Answer: We have expanded the description of hot isostatic pressing.

In the text:

Two ZnSe samples were subjected to hot isostatic pressing (HIP). Custom-built HIP equipment UGL-2000 with a graphite heater was used. Samples were treated simultaneously in one process in graphite containers placed in different temperature zones: - 900°C and 1200°C. Temperature was controlled by the C-type thermocouples; argon pressure was 100 MPa and the holding time was 24 hours.

Question 4) How the beam diameter changes?

Answer: The beam diameter was determined by the Galilean telescope. We didn’t change the beam diameter.

It has been described in the text:

The linearly polarized beam at 2091 nm was focused on the surface of the tested samples using the Galilean two-lens telescope. The beam diameter on the surface (measured by the “knife-edge” method [18]) was estimated as 0.27 mm at the e^-2 intensity.

Question 5) How the collaboration is retarded with oxygen?

Answer: We are not sure what was asked in this comment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Referee report on “Effects of Processing Technology of CVD-ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe Polycrystalline Optical Elements on the Damage Threshold Induced by a Repetitively-Pulsed Laser at 2.1 µm” by Nikolay Yudinet al.

This is a quite good article that will be suitable for publication after taking into account the few following suggestion, which will certainly improve this manuscript.

1.     Lines 33, 36, 41 and 42. The supporting references are needed in the end of sentences.

2.     Lines 47 and 49 - supporting references are needed.

3.     Line 60. What is (in terms of physics) and manifests itself laser damage and how it differs, for example, from neutron or proton irradiation.

4.     Line 98-99. How are these samples fundamentally different?

5.     Lines 223-227. Note that recently, few luminescence studies of ZnSe luminescence materials were reported. See below and references therein:

Degoda, V. Y., Podust, G. P., Doroshenko, I. Y., & Pavlova, N. Y. (2022). Phosphorescence and conduction current relaxation in ZnSe crystals. Optical Materials, 129, 112460.

Brodyn, M. S., Degoda, V. Y., Alizadeh, M., Podust, G. P., Pavlova, N. Y., & Kozhushko, B. V. (2020). Deep traps concentrations in ZnSe single crystals. Materials Science and Engineering: B, 258, 114570.

6.     Are there any spectral indications of the presence of F centers in the investigated samples? See, for example: Popov, A.I.; Kotomin, E.A.; Maier, J. Basic properties of the F-type centers in halides, oxides and perovskites. Nucl. Instrum. Methods Phys. Res. Sect. B 2010, 268, 3084–3089.

7.     Before conclusion, is it possible to draw a band picture indicating the main impurity levels and possible radiative recombinations?

Author Response

Question 1-2) Lines 33, 36, 41 and 42. The supporting references are needed in the end of sentences. Lines 47 and 49 - supporting references are needed.

Answer: The corresponding references have been added.

Question 3) Line 60. What is (in terms of physics) and manifests itself laser damage and how it differs, for example, from neutron or proton irradiation.

Answer: The laser-induced damage is caused by the interaction of optical waves with materials. The origin of the effect differs in many ways from the damage induced by the particle (neutron or proton) irradiation. Several important features of the optical damage of materials include the one-photon and multi-photon absorption and the interaction of the electric field of an optical wave with the internal material fields. This effect was described in many papers and books, including those that were referenced in the paper (see, for example:  “Laser-Induced Damage in Optical Materials; Ristau, D., CRC Press, 2014; ISBN 9781439872178.”).

Question 4) Line 98-99. How are these samples fundamentally different?

Answer: The samples are made on different equipment, but we believe that the manufacturing processes are very similar; there are only small nuances in the organization of the synthesis.

Question 5) Lines 223-227. Note that recently, few luminescence studies of ZnSe luminescence materials were reported. See below and references therein:

Degoda, V. Y., Podust, G. P., Doroshenko, I. Y., & Pavlova, N. Y. (2022). Phosphorescence and conduction current relaxation in ZnSe crystals. Optical Materials, 129, 112460.

Brodyn, M. S., Degoda, V. Y., Alizadeh, M., Podust, G. P., Pavlova, N. Y., & Kozhushko, B. V. (2020). Deep traps concentrations in ZnSe single crystals. Materials Science and Engineering: B, 258, 114570.

Answer: We agree that a similar luminescence effect was recently observed and reported. We added the references to the mentioned papers and included an explanation of this effect, which was attributed to recombination of free electrons on defect centers related to the oxygen.

Changes in Lines 223-226:

Similar red luminescence in ZnSe induced by the X-ray or visible light or even caused by the thermal excitation was recently reported ^26–29. The luminescence may be explained by a radiative recombination of free electrons with holes localized on the oxygen-related defect centers of the chalcogenides ^27–29.

Additions in the references

28. Brodyn, M. S., Degoda, V. Y., Alizadeh, M., Podust, G. P., Pavlova, N. Y., & Kozhushko, B. V. (2020). Deep traps concentrations in ZnSe single crystals. Materials Science and Engineering: B, 258, 114570.
29. Degoda, V. Y., Podust, G. P., Doroshenko, I. Y., & Pavlova, N. Y. (2022). Phosphorescence and conduction current relaxation in ZnSe crystals. Optical Materials, 129, 112460.

Question 6) Are there any spectral indications of the presence of F centers in the investigated samples? See, for example: Popov, A.I.; Kotomin, E.A.; Maier, J. Basic properties of the F-type centers in halides, oxides and perovskites. Nucl. Instrum. Methods Phys. Res. Sect. B 2010, 268, 3084–3089.

Answer: We haven’t noticed any indications of the presence of F centers in the investigated samples.

Question 7) Before conclusion, is it possible to draw a band picture indicating the main impurity levels and possible radiative recombinations?

Answer: Since the origin of the reported red luminescence has not been discussed in detail and is not the main subject of this paper, it might not be the best option to include the band figure into the text.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Editor,

the manuscript submitted by Yudin N. and co-workers is a systematic work about the laser-induced damage thresholds in chemical vapour deposition produced ZnSe based materials.

The starting points of this work are the pure ZnSe and the Cr2+ and Fe2+ doped ZnSe, which are subsequently treated in different ways to find the optimal damage threshold.

Overall, this systematic and rather comprehensive work is well structured. However, some sentences reported throughout the manuscript are not enough supported. As a consequence, this work might be ready for publication on Ceramics after the following major comments are amended by the authors.

1.When presenting and discussing the results on the damage threshold of HIP treated ZnSe, the authors observe a non monotonic trend. Specifically, when trested at 900°C, the LIDT is significantly lower than the untreated sample, whereas for the sample treated at 1200°C, it increases back, despite being still below the LIDT value of the untreated sample. Such a phenomenon has been ascribed to a more complete diffusion process of impurities in the volume of the ZnSe sample at higher temperature. Despite realistic, such explanation is not actually supported by any experimental evidence. The authors should implement their discussion and support more strongly their statement.

2.The authors mention that the sample produced by PromLab features a larger average grain size. Also in this case, this statement is not supported by any experimental evidence.

3.When discussing Figure 5, the authors notice that the LIDT decreases while increasing the exposure time. However, they do not comment the fact that the slope of the damage probability apparently decreases upon increasing the exposure time. Can the authors comment this aspect?

4.In the discussion of the LIDT dependence on the PRR, the authors mention that the Se and Ar treated samples show a decrease of 18% and 5%. However, the data are not reported. The authors should consider adding these data at least in the Supporting Information file.

5.Analogously to my comment #4, the authors say that the LIST of the Zn treated ZnSe and Cr-doped ZnSe samples are comparable, but they do not show the experimental data.

6.The discrepancies between the abserved behaviours in the ZnSe samples produced by different manufacturers is ascribed to an unequal number of inclusions due to different controls in the gas flow during the sample production. However, such comment is temptative as it is not supported by evidencies. Can the authors make any elemental analyses on their samples?

Author Response

Question 1) When presenting and discussing the results on the damage threshold of HIP treated ZnSe, the authors observe a non monotonic trend. Specifically, when trested at 900°C, the LIDT is significantly lower than the untreated sample, whereas for the sample treated at 1200°C, it increases back, despite being still below the LIDT value of the untreated sample. Such a phenomenon has been ascribed to a more complete diffusion process of impurities in the volume of the ZnSe sample at higher temperature. Despite realistic, such explanation is not actually supported by any experimental evidence. The authors should implement their discussion and support more strongly their statement.

Answer: We have expanded the descriptions and made references that we believe can support our hypothesis.

Question 2) The authors mention that the sample produced by PromLab features a larger average grain size. Also in this case, this statement is not supported by any experimental evidence.

Answer: We have added the average grain size into the text.

In the text:

The studied PromLab material has a 50% larger average grain size of 61 µm compared to the II-VI one of 40 µm. Various studies showed that in CVD-ZnSe both impurity ions and inclusions are predominantly located along grain boundaries ^3,25.

Question 3) When discussing Figure 5, the authors notice that the LIDT decreases while increasing the exposure time. However, they do not comment the fact that the slope of the damage probability apparently decreases upon increasing the exposure time. Can the authors comment this aspect?

Answer: We noted that zero-probability of LIDT decreases as the exposure time and PRR increase in all tested ZnSe or Fe:ZnSe samples. This fact appears to be in good agreement with the incubation phenomenon when the LIDT fluence decreases with the increase in the number of pulses during irradiation. However, the slope of the damage probability apparently decreases upon increasing the exposure time but in the ZnSe samples only. We added in the text information about decreasing the 0-poability LIDT fluence, and an explanation of the slope change for the ZnSe samples.

In the text:

Note, that the slope of the damage probability in ZnSe samples apparently decreased upon increasing the exposure time (Fig. 5), however, this effect was absent in the Fe²⁺:ZnSe samples (Fig. 9b). This may be explained by an additional annealing of the high-quality irradiated spot in ZnSe during long exposure, and it isn’t valid for the annealed Fe²⁺:ZnSe samples.

Question 4) In the discussion of the LIDT dependence on the PRR, the authors mention that the Se and Ar treated samples show a decrease of 18% and 5%. However, the data are not reported. The authors should consider adding these data at least in the Supporting Information file.

Answer: We added the LIDT data for the ZnSe_org, ZnSe_Se and ZnSe_Zn in the table 2.

Question 5) Analogously to my comment #4, the authors say that the LIST of the Zn treated ZnSe and Cr-doped ZnSe samples are comparable, but they do not show the experimental data.

Answer: We added the LIDT data for the Cr:ZnSe_Se_and Cr:ZnSe_Zn in the table 3.

Question 6) The discrepancies between the abserved behaviours in the ZnSe samples produced by different manufacturers is ascribed to an unequal number of inclusions due to different controls in the gas flow during the sample production. However, such comment is temptative as it is not supported by evidencies. Can the authors make any elemental analyses on their samples?

Answer:

It is known that the impurity content in the samples is at ppm level or less, which leads to a large error of elemental analysis. And it is not known exactly which impurities have the greatest influence on LIDT. Finding excess zinc or selenium (about 10-6 mol) by elemental analysis on matrix background is impossible. However, approximately equal LIDT in the initial PromLab and II-VI ZnSe and in material manufactured by INOPTICS after the annealing in argon allows us to assume that the difference between the materials is mainly in stoichiometry. Short annealing at the moderate temperature is unlikely introduce other structural changes that would increase LIDT. The difficulty of controlling the gas flow in a reactor is well-known; see, for example, https://doi.org/10.1117/12.277062

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have significantly improved the manuscript, so now it can be recommended for publication

Author Response

Thank you for your thorough review.

Reviewer 3 Report

Question #1) Despite the authors claim they had improved their work, no modifications have been made to provide a better understanding of the concern issued in my original report. Specifically, I was wondering if the authors knew why treating a sample at lower temperature (900°C) as a larger effect than treating it at a higher temperature (1200°C). The data and the discussion I am referring to is Figure 3 compared to dataset #1 of Figure 2.

Question #2) Despite the authors now report in the manuscript the supposed dimensions of the grain sizes of the PromLab materials, these are not supported by experimental data that should be reported, at least, in the supplementary information file.

Question #3) In the sentence the authors added after my original comment, they compare the trends of the "pure" ZnSe sample reported in Figure 5 -the subject of my comment- and those of the Fe doped ZnSe sample shown in Figure 9b, claiming that the latter has no dependence on the exposure time of the damage slope. However, looking at the data, the trend seems to be less pronounced, but still present, thus making the reply to my comment not solid.

Question #4) Thank you for adding these data in agreement with my comment.

Question #5) Thank you for adding these data in agreement with my comment.

Question #6) Thank you for clarifying this aspect.

Author Response

Thank you for your thorough review.

Question #1)  Despite the authors claim they had improved their work, no modifications have been made to provide a better understanding of the concern issued in my original report. Specifically, I was wondering if the authors knew why treating a sample at lower temperature (900°C) as a larger effect than treating it at a higher temperature (1200°C). The data and the discussion I am referring to is Figure 3 compared to dataset #1 of Figure 2.

ANSWER

We compared HIP-treated (900°C and 1200°C) samples and annealed in argon (1050°C), because both of these procedures are performed in argon. There is an explanation for the differences in sample behavior (lines 308-338). Everything about these differences (mainly impurity composition) is even more related to the original material, we added a mention of it at the beginning of the explanation.

Question #2) Despite the authors now report in the manuscript the supposed dimensions of the grain sizes of the PromLab materials, these are not supported by experimental data that should be reported, at least, in the supplementary information file.

ANSWER

We added photographs of the microstructure of original samples from different manufacturers in supplementary materials.

Question #3) In the sentence the authors added after my original comment, they compare the trends of the "pure" ZnSe sample reported in Figure 5 -the subject of my comment- and those of the Fe doped ZnSe sample shown in Figure 9b, claiming that the latter has no dependence on the exposure time of the damage slope. However, looking at the data, the trend seems to be less pronounced, but still present, thus making the reply to my comment not solid

ANSWER

We agree that a weak dependence of the exposure time of the Fe:ZnSe damage slope still exists. For this reason we changed the sentence in the text:

“Note, that the slope of the damage probability in ZnSe samples apparently decreased upon increasing the exposure time (Fig. 5), however, this effect was measured to be much weaker in the Fe²⁺:ZnSe samples (Fig. 9b).”

Round 3

Reviewer 3 Report

Comment #1) The discussion about the effect of the HIP treatment at two different temperature has been reported by the authors, with references supporting that their assumptions have been investigated in previously published works.

Comment #2) Thanks to the authors for adding in the supporting information file the micrographs of the investigated samples. Anyway, it is very hard for the reader to quantitatively evaluate that the statements made in the manuscript are correct. To prove that the average size of the crystals are those reported in the text (61 and 40 um), a statistical analysis of the images should be done by the authors and provided to the readers.

Comment #3) Thanks to the authors for finally acknowledging that there is a trend in the slopes of the damage probabilities as a function of the excitation fluence upon increasing the exposure duration. However, my original comment wondered about whether the authors could provide an explanation for such a behavior, since this is a critical aspect for pratical technological application of these materials.