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Optical Society of Korea (한국광학회)
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Design of an Nd:YAG Slab Structure for a High-power Zigzag Slab Laser Amplifier Based on a Wavefront Simulation

  • Received : 2019.01.14
  • Accepted : 2019.04.16
  • Published : 2019.06.25
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Abstract

An Nd:YAG slab structure was designed for a high-power zigzag slab laser amplifier based on computational simulation of the wavefront distortion. For the simulation, the temperature distribution in the slab was calculated at first by thermal analysis. Then, the optical path length (OPL) was obtained by a ray tracing method for the corresponding refractive index variation inside the slab. After that, the OPL distribution of the double-pass amplified beam was calculated by summing the results obtained for the first and second passes. The amount of wavefront distortion was finally obtained as the peak-to-valley value of the OPL distribution. As a result of this study, the length and position of the gain medium were optimized by minimizing the transverse wavefront distortion. Under the optimized conditions, the transverse wavefront distortion of the double-pass amplified beam was less than $0.2{\mu}m$ for pump power of 14 kW.

Keywords

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FIG. 1. Conceptual scheme of the Nd:YAG zigzag slab amplifier for design optimization (Ls: total length of the slab, Ld: length of the Nd:YAG, Xd: distance from the left end of the slab to the right end of the Nd:YAG, θ1: incident angle of the first amplification pass, θ2: incident angle of the second amplification pass).

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FIG. 2. Temperature distributions (a) for slab length axis at the center of the width and (b) for slab width axis at the temperature peak position of the length when the total pump power was 14 kW. Here, Ld and Xd are 100 mm and 10 mm, respectively, so that the lengths of the pure YAGs located at both ends would be equal.

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FIG. 3. OPL distributions for transverse axis of the amplified beam when Ld and Xd were 100 mm and 10 mm, respectively: (a) OPL distributions for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°), (b) OPL distribution for the double pass.

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FIG. 4. OPDs with respect to the Nd:YAG length (Ld) for transverse axis of the amplified beam when the values of Xd were determined to satisfy Xd =(Ls - Ld)/2 so that the Nd:YAG was positioned at the center of the total slab length: (a) OPDs for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°), (b) rescaled OPDs near Ld = 97.3 mm, (c) rescaled OPDs near Ld = 104.4 mm, (d) OPDs for the double pass.

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FIG. 5. OPL distributions for transverse axis of the amplified beam at a local maximum point (P1) where Ld = 97.3 mm and at a local minimum point (P2) where Ld = 101.4 mm: (a) OPL distributions for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) at P1, (b) OPL distribution for the double pass at P1, (c) OPL distributions for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) at P2, OPL distribution for the double pass at P2.

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FIG. 6. OPDs with respect to the Nd:YAG position (Xd) for transverse axis of the amplified beam: (a) OPDs for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) when Ld = 97.3 mm, (b) OPDs for the double pass when Ld = 97.3 mm, (c) OPD values for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) when Ld = 101.4 mm, (d) OPD values for the double pass when Ld = 101.4 mm.

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FIG. 7. OPL distributions for transverse axis of the amplified beam when Ld = 97.3 mm at a local maximum point (P3) where Xd = 10.3 mm and at a local minimum point (P4) where Xd = 9.3 mm: (a) OPL distributions for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) at P3, (b) OPL distribution for the double pass at P3, (c) OPL distributions for the first pass (θ1 = 22°) and for the second pass (θ2 = 18.5°) at P4, OPL distribution for the double pass at P4.

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