Two-Photon Absorption in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 Crystals
, Valery I. Kovalev 1, Nikita S. Semin 1, Pavel A. Danilov 1, Sergey I. Kudryashov 1, Andrey V. Koribut 1 and Elizaveta E. Dunaeva 2
Round 1
Reviewer 1 Report
I attach my comments in a pdf file
Comments for author File: 
Comments.pdf
Author Response
The manuscript report experimental values of two-photon absorption in CSVO at 515 nm, for both axis orientation and two different Ca/Sr ratio. This crystal has gain recent interest or stimulated Raman scattering and short pulse generation.
Q.1 I find it impossible to judge the novelty and the manuscript’s relevance as it seems to be a copy of a previous experiment, i.e. ref [5]. This reference is not accessible because not yet published, by the same authors. The presented results, i.e. the TPA coefficients are also the same, presumably, as in ref. [5]. The entire discussion on experimental results relies on a comparison with ref [5], which is not accessible and most likely identical as this manuscript, except the focal length of the lens used.
As a result, I suggest the editor to reject this manuscript.
R.1.1 We apologize for a discomfort caused by the delayed availability of this paper (Ref [5] in the submitted manuscript). It is now completed: Kinyaevskiy, I.O.; Kovalev, V.I.; Koribut, A.V.; Dunaeva, E.E.; Semin, N.S.; Ionin, A.A. Stimulated Raman scattering of 0.3-ps 515-nm laser pulses in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals. Opt Spectrosk, 2023, 131(2), 207-211, DOI: 10.21883/OS.2023.02.55007.8-23.
R.1.2 We believe that the accessibility of Ref. [5] will relieve the pretensions. One can easily find that this manuscript is not a copy of Ref [5]. The Ref [5] was focused on stimulated Raman scattering (SRS) of 0.3-ps 515-nm laser pulses in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals, as it stated in that paper title. Genuinely TPA coefficients were determined in Ref [5] and their difference for Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals was found. However, these data were obtained in the conditions of essential transformation of propagating laser radiation due to self-phase modulation and SRS. In the current work contribution of these effects was reduced by using a longer focus length (f1 = 9 cm). Also, in the current work the TPA coefficient was measured for different polarization-to-c-axis orientations, which was absent in Ref [5].
Q.2 Moreover, 7 out 18 references are self-references, which is not a good indication of proper literature research.
R.2. Four of “7 self-references” introducing the crystals under study. The major published results on growth and characterization of such crystals belong to the group from GPI. Dr E. Dunaeva is the co-author in our work because she is the expert in manufacturing and characterization of such crystals. Since she is the member of the GPI group co-authored published “Four of “7 self-references”, we believe that appeared “excessive” self-referencing pardonable for the whole team of co-authors from the Lebedev Institute and GPI.
Q.3 Line 48: does “pulse-periodic” simply mean pulsed laser with repetition rate 1 kHz?
R.3. The words “pulse-periodic” removed on line 48.
Q.4 Line 91: I believe the authors mean “Rayleigh range” and not waist length. This is unclear.
R.4 The words “waist length” replaced by “doubled Rayleigh range” on lines 96-97.
Q.5 Equations 3-6 as well as corresponding descriptions are trivial knowledge of Gaussian beams. Is there a real need for such derivation?
R.5 Among Equations 3-6 only Eqs 4-6 may look as the “trivial knowledge of Gaussian beams”. However, that is not so because the Gaussians, which conventionally used for characterization spatial, Eq.4, and temporal, Eq.5, distributions, are different. Respectively, their presence in the manuscript logical and appropriate.
Q.6 The manuscript also need extensive English editing before eventual publication.
R.6 English was checked and edited over the whole manuscript by native English-speaking colleague Professor A. Walker.
Reviewer 2 Report
The work of Igor O. Kinyaevskiy et al. is devoted to the study of the process of two-photon absorption in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals. The results of studies of the optical properties of crystals, which can find application in the field of lasers or nonlinear optics, are always of a certain value. And therefore, they are of interest to researchers in these fields.
The disadvantages of the work include the fact that it is impossible even to estimate the accuracy of the given composition of the crystals under study from the data contained in manuscript. This disadvantage is often encountered in such materials science works. Therefore, it is difficult to exclude the influence of possible uncontrolled impurities on the properties of crystals under study. It would be good if the authors could add to the text of the article information they may have on this issue.
In general, the work under consideration is a well-made publication on the study of the properties of new optical materials, and therefore it can be published.
Author Response
Reviewer 2
The work of Igor O. Kinyaevskiy et al. is devoted to the study of the process of two-photon absorption in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals. The results of studies of the optical properties of crystals, which can find application in the field of lasers or nonlinear optics, are always of a certain value. And therefore, they are of interest to researchers in these fields.
Q1. The disadvantages of the work include the fact that it is impossible even to estimate the accuracy of the given composition of the crystals under study from the data contained in manuscript. This disadvantage is often encountered in such materials science works. Therefore, it is difficult to exclude the influence of possible uncontrolled impurities on the properties of crystals under study. It would be good if the authors could add to the text of the article information they may have on this issue.
R1. In reply to Q1, the sentence is added on page 2, section “2. CSVO crystals”, lines 64-67: “The crystals were optically homogeneous, the deviation of the stoichiometric composition and other impurities in the crystals were not detected within a measurement error of 0.05 at% [2]. Anomalous birefringence did not exceed 1.3×10−5 cm−1.”
Reviewer 3 Report
1- The authors should explain what makes this work unique and how it differs from previous research.
2- More details, including the model, must be added regarding the laser system that is being used.
3- More details, must be added regarding the crystals that are being used.
4- Please explain in the experimental setup how you control the crystal orientation with respect to the laser polarization.
5- Please explain in the text how you vary the incident pulse energy.
6- Nothing is mentioned in the text about the uncertainty in the measurements, so please discuss this issue in the text.
7- Is there a dependence of the measured TPA coefficient on the laser polarization, laser repetition rate, and laser beam intensity?
8- While only one crystal was investigated as shown in Fig. 4, the title indicates that the investigations will study the TPA of the CSVO crystals. Please clarify this issue.
Author Response
Reviewer 3.
Q.1 The authors should explain what makes this work unique and how it differs from previous research.
R.1 Information on the TPA coefficient in Ca3(VO4)2 can be found in two publications [5,9]. However, the coefficients they report differ by nearly an order of magnitude. This work is the first systematic study of the two-photon interband absorption (TPA) effect in SRS-active crystals Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2. In contrast to previous works, Refs [5] and [9], measurements made in the conditions when effects of SRS, self-phase modulation broadening and TPA-induced absorption substantially reduced. The absolutely unique results are discovery that the magnitudes of TPA coefficients in these crystals i) don’t correlate with materials bandgap and ii) strongly depend on whether the crystal c-axis perpendicular or parallel with respect to the laser radiation polarization.
Q.2 More details, including the model, must be added regarding the laser system that is being used.
R.2 The key for our study parameters of the laser system, i.e. pulse duration and energy, pulse repetition rate, spatial mode of the beam, radiation wavelength and state of polarization exist in Section 3 Experimental setup. To meet the request, we adding to the text the data on laser model and the laser supplier (page 3, line 89): “Satsuma, Amplitude laser, France”.
The laser system is presented in the supplier website: https://amplitude-laser.com/products/femtosecond-lasers/satsuma/
Q.3 More details, must be added regarding the crystals that are being used.
R.3.1 . In reply to this request, the sentence is added on page 2, section “2. CSVO crystals”, lines 64-67: “The crystals were optically homogeneous, the deviation of the stoichiometric composition and other impurities in the crystals were not detected within a measurement error of 0.05 at% [2]. Anomalous birefringence did not exceed 1.3×10−5 cm−1.”
R.3.2 Also the information on the refractive index added on page 2, section “2. CSVO crystals”, lines 72-74: “The dotted line in Figure 1 indicates Fresnel reflection level calculated for refractive index n=1.9 (refractive index of CSVO, x=0, are 1.902 and 1.877 for ordinary and extraordinary polarizations at λ≈0.546 μm [3]).”
Q.4 Please explain in the experimental setup how you control the crystal orientation with respect to the laser polarization.
R.4 The orientations of laser beam linear polarization and the c-axis of samples are known. The angle between the linear polarization of the laser beam and the CSVO optical c-axis was controlled with the accuracy of ~3o by the corresponding orientation/installation of the samples. Page 3, lines 100-101 “The angle between the linear polarization of the laser beam and the CSVO optical c-axis was set by rotation of the sample.”
Q.5 Please explain in the text how you vary the incident pulse energy.
R.5 The sentence is added on page 3, line 93: ” … and it was varied by a polarizer-attenuator.”
Q.6 Nothing is mentioned in the text about the uncertainty in the measurements, so please discuss this issue in the text.
R.6 The sentence is added on page 5, lines 161-162: ”The uncertainties in measurements (Figure 4) are determined by fluctuations of input (±3 %) and transmitted (±10 %) pulses energy.”
Q.7 Is there a dependence of the measured TPA coefficient on the laser polarization, laser repetition rate, and laser beam intensity?
R.7 Revealed essential dependence of TPA coefficients on orientation of the crystal c-axis with respect to the laser radiation polarization (parallel Fig. 4a or perpendicular Fig. 4b) is absolutely unique result, which, we believe, may have profound effect on the physics of interaction of high-power laser radiation with crystals. Dependence of the measured TPA coefficient on the laser repetition rate was not investigated (only one rep. rate, i.e. 1 kHz, used). The dependence on the laser beam intensity not detected.
Q.8 While only one crystal was investigated as shown in Fig. 4, the title indicates that the investigations will study the TPA of the CSVO crystals. Please clarify this issue.
R.8 TPA was investigated in both Ca2.7Sr0.3(VO4)2 (CSVO, x=0.3, line 1 in Fig 4a,b) and Ca3(VO4)2 (CSVO, x=0, line 2 in Fig 4a,b).
Round 2
Reviewer 1 Report
I was not able to access reference [5] online on the website of the publisher. I leave the decision to the editor.
Reviewer 3 Report
In response to my previous suggestions and concerns, the authors have made reasonable changes to the manuscript. Overall, the manuscript reads well and clarifies the authors' work. In my opinion, the manuscript contains currently all information and is ready for publishing in the Journal " photonics " as a regular article.
