Research on the Thermal Effect of Micro-Channel Cooled Thin-Slab Tm:YAP Lasers

Round 1

Reviewer 1 Report

Thermal effect is very important for the design of high-power solid-state lasers. The research results of this paper are very interesting. However, there are a few small issues that need to be explained before the paper is accepted.

1.      The accuracy of grid division has a significant impact on the results of finite element analysis, so it is necessary to explain the accuracy of grid division in the thermal effect analysis in this paper.

2.      In the line 75, "the spots of the pump light is 0.5×2mm", but what is the intensity distribution of the pump light? Gaussian distribution, uniform distribution or else? Please explain it.

3.      In the line 126, Please explain the principle of designing the lengths of each section of the gradient doping Tm:YAP.

4.      According to Figure 9, the number of micro-channels was doubled when t₁=0.2. Is it considered to further reduce the width of the micro-channel or some other methods to obtain better heat dissipation effect?

5.      Use Fig. instead of Figure. in the manuscript.

6.      There are some wrong citation format in the manuscript, such as Ref[8] Ref[12] and Ref[14].

Author Response

        Thank you for your comments.

1. In theory, the finer the mesh division, the higher the accuracy of the obtained analytical solution, but at the same time, the calculation time will also greatly increase. Therefore, considering both computational efficiency and accuracy, the grid division is selected as "Normal".
2. The intensity distribution of the pump light is flat-top and has added the description in the paper.
3. For the gradient doping Tm:YAP, the principle of the design is to ensure that the absorbed pump power in each doping section is the same based on the absorption coefficient.

4. As shown in the Figure 9(b), the temperature distribution in the crystal with the t₁ of 0.2 is very close to Figure 2 (b) which is obtained under the condition that the cooling surface temperature is equal to the cooling water temperature. So further reducing the channel width has little effect on improving the thermal effect in our model, while at the same time, reducing the channel width will increase the difficulty of machining micro-channels.

5.   In the latest article published by Photonics, the figures and tables used "Figure" and "Table", so the "Figure" and "Table" in our manuscript have not been abbreviated.

6. Has revised the format of the references.

Reviewer 2 Report

The manuscript investigated the temperature, stress and end face deformation in Tm:YAP crystal under high pump power with the finite element method. To reduce the temperature gradient in the crystal, the thermal effects in the gradient doping Tm:YAP have been studied and compared to the uniform doping Tm:YAP. The results show that with the same pump power of 200 W and the same cooling conditions, the maximum temperature difference inside Tm:YAP decreases from 58 K to 25 K after gradient doping. The results can provide design guidelines for the high power 2-μm solid-state lasers. However, before the paper is accepted, there are still several changes to be made.

1. The Indium is used between the Tm:YAP and heat sink in the Fig. 1. However, the Indium layer does not appear for the thermal analysis in the Fig. 9. Please add comments on it.

2. The intensity distribution characteristics of pump light also have impact on the thermal effect inside the crystal. Therefore, it is necessary to explain the spatial distribution characteristics of the pump light used in the finite element analysis.

3. The manuscript mentioned that “The size of h1 and h2 are 0.5 mm and 6 mm respectively.”. Please explain why the size of h1 is 0.5 mm.

4. The manuscript should be polished. There are some typos and grammar mistakes, such as “W/m3.” in line 85, page 3. 

Author Response

         Thank you for your comments.

1. The indium layer between the Tm:YAP to the heat sink is usually very thin (no more than 50μm), so the heat is transferred very quickly from the Tm:YAP to the heat sink. Therefore, in the finite element analysis, the indium layer is neglected. The explanation of the indium layer has been added in the paper

2. The intensity distribution of the pump light is flat-top and has added the description in the paper.

3. It is obvious that the smaller of the h₁, the more conducive to heat dissipation. According to reference17, considering the requirements of strength, the size of h1 is 0.5 mm. 

4. Has revised some typos and grammar mistakes and the modified parts are marked in red.

Reviewer 3 Report

In the following paper, Research on the thermal effect of micro-channel cooled thin slab Tm:YAP lasers, the temperature, stress, and end face deformation in Tm:YAP crystal under high pump power are analyzed using the finite element method and the heat conduction equation. In my opinion, the highlights of the manuscript are not clear, the novelty of the manuscript is not strongly addressed, and lack of experimental investigations as well. Therefore, the manuscript seems to not fit to be published in Photonics Journal.

Author Response

Thank you for your comments.

Our project includes the simulation, the system design and the implementation. This manuscript shows our simulation research results, which need to be completed firstly and correctly in the design of solid-state lasers. So, in this manuscript, combined with the gradient doping technology and heat sink with micro-channel structure, the temperature, stress and end face deformation in Tm:YAP crystal under high pump power are analyzed theoretically. We report our periodic research and also would like to listen to your expert opinions. In this way, we could optimum our design work furthermore. Regarding to the experiments, our following research will focus on it. Meanwhile, the corresponding results will be reported as soon as we finish the experiments.