Second Harmonic Generation Non linear optics

Non linear optics

1. Effects of Grain Morphology on Nonlinear Conversion Efficiency of Random Quasi-Phase Matching in Polycrystalline Materials SUJIT PAUL(22PEE006)  supervised by: Dr. Minakshi Deb B arma DEPARTMENT OF ELECTRICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY AGARTALA TRIPURA-799046, INDIA November – 2023

2. Contents Random quasi-phase matching Advantage of RQPM over traditional QPM Grain morphology Vornoi tessellation Meshing Polycrystalline model of ZnSe Grain size distribution SHG in polycrystalline ZnSe SHG power calculation SHG power graph plot Future work reference 2

3. Random Quasi-phase Matching Random quasi-phase matching (RQPM) is a technique used in nonlinear optics to overcome the phase-matching limitations in certain nonlinear processes. RQPM introducing randomly varying domain structures within the nonlinear crystal. These structures break the periodicity of conventional phase-matching techniques, and allowing for broader acceptance bandwidth. 3

4. Advantage of RQPM over traditional QPM 1. Broadened acceptance bandwidth: Traditional QPM structures are designed for specific wavelengths, and achieving phase matching over a broad range of wavelength can be challenging . However, RQPM introduces random variations in the domain structure, enabling efficient interaction over a wider range of wavelengths. This broader acceptance bandwidth allows for greater flexibility in choice of input and output wavelengths. 2. Simplified fabrication: Achieving precise periodic domain structures for traditional QPM can be technically challenging and time-consuming. RQPM relies on the introduction of random domain structures which can be simpler to fabricate. This simplification in fabrication process can reduce the manufacturing complexity and cost. 3 . Improved conversion efficiency: In certain cases RQPM can provide enhanced conversion efficiency. RQPM can mitigate the effects of phase mismatch and reduce the impact of spatial walk-off, leading to improved efficiency in nonlinear processes. 4

5. Grain Morphology In material science grain morphology refers to the arrangement, size, shape, and orientation of individual each grains within a material. The materials are composed of numerous small crystalline group of element called grains, and to understanding the grain morphology is essential because it greatly influences the material's properties and behavior . For monocrystalline the unit cells are interlock each other in same way and crystallographic orientation, e ven at infinite length scales, each atom is related to every other equivalent atom.   For polycrystalline all the grains have random crystallographic orientation. Each grain can be thought of as a single crystal, within which the atomic structure has long-range order, there is no relationship between neighboring grains. For amorphous the material have random and disordered atomic arrangement. Amorphous materials, like window glass, have no long-range order at all 5

6. Vornoi tessellation Vornoi tessellation created uniform distribution of surface plane of every seeds and closed together without any gap between them . In a Voronoi tessellation, each point in space belongs to the region associated with the nearest seed. In recent years, several techniques for the computer simulation of grain growth have been developed, including Monte Carlo Potts models, vertex tracking, front tracking, cellular automata and phase-field approaches. These methods were initially developed for the 2D case. For 3D case three dimensional aggregates with a relevant number of grains have been successfully addressed using Monte Carlo Potts models. 6

7. M eshing Meshing is often used in software-based simulation for Finite Element Analysis (FEA ). Mesh is generated by connected of each element called nodes, each nodes may have two or more then two element connected to it. A collection of this elements is called mesh. The assembly of these element and nodes is called finite element model. The finer the mesh, the more accurately the 3D model will be defined. the mesh is prepared as a regular lattice with implied connectivity between elements. 7

8. Polycrystalline model of ZnSe To study the detailed effects of the statistical grain morphology and the second harmonic generation (SHG) we design a random structures generated by a realistic grain growth model. T he model is generated by Neper software , and we calculate the effect of SHG power for grain size variation. We design 3 model by neper software, generated polycrystalline model of 350 grain dimension 500 500 500 . Model–(a): generated polycrystalline model with mean = 95 ,and stander deviation = 48 . Model –(b): generated polycrystalline model with mean = 95 ,and stander deviation =30. Model –(c): generated polycrystalline model with mean =130,and stander deviation = 48 .   8

9. Polycrystalline model of ZnSe (a) (b) (c) (d) Fig: the preset value (mean and standard deviation) in (a) mean=95,sigma=48 (b) mean=95,sigma=30 and (c)mean= 130,sigma=48.(d)meshing of image fig:(a) 9

10. Model–(a): generated polycrystalline model of 350 grain dimension 500 500 500 with mean = 95 ,and stander deviation = 48 .   10 17 52 80 73 58 43 17 7 No. of grains

11. Model –(b): generated polycrystalline model of 350 grain dimension 500 500 500 with mean = 95 ,and stander deviation = 30 .   11 17 107 89 86 42 7 No. of grains Because of lower standard deviation the maximum grain size variation relies on 90 to 100 micrometer range

12. Model –(c): generated polycrystalline model of 350 grain dimension 500 500 500 with mean = 130 ,and stander deviation = 48 .   12 No. of grains

13. Second Harmonic Generation In Polycrystalline Znse The SHG field solution can be expressed in an integral form, Where is the is the fundamental electric field is the phase mismatch, = 0 is the lower limit of the integral formula L, is the total interaction length   13

14. Continued.. it is assume that input electric field is oscillating along the X-axis and the polarization of SHG field can be along both the X and Y-axis. So the resulting non-linear coefficient in an arbitrary grain are , Where = 20 pm/V , And R   14

15. SHG Power calculation We use Kerr-lens mode-locked Cr:ZnS laser with a central wavelength of 2.35 µm and The OPO had a 90-mW pump threshold, and produced an ultra broadband spectrum spanning 4.7 μ m . Wavelength. the optical parametric oscillator (OPO) action has several advantages:- i )High peak intensity that can be achieved with no multi-photon absorption, ii) Very low group velocity dispersion (GVD) at OPO frequencies (≈ 4.7 μm ) - a prerequisite for broadband output SHG power can be calculated by, Input intensity(I)= = = w/   =   15  

16. Statistic data of sample (a) and output power SL n0. Grain diameter(micrometer) Euler Angle-Roe(degree) (θ, Φ , ψ ) SHG power(GW) For X-polarization SHG power(GW) For Y-polarization 1 99.372 (252.1926, 123.3116, 125.215) 1935.7 160.5741 2 90.618 (358.8566, 58.574, 298.048) 47.2866 61.4818 3 59.622 (108.9147, 115.2516, 5.756) 0.3815 20.1812 4 78.980 (337.7185, 60.290376, 16.0723) 10.1958 179.6962 5 117.957 (195.9331, 119.9577, 138.6314) 211.8289 373.1188 6 73.511 (195.5058, 100.6249, 275.092) 1.6264 19.4771 7 85.290 (288.4981, 44.5054, 212.1409) 496.2432 79.8908 8 107.797 (262.1158, 61.2649, 229.3104) 582.2348 45.1935 9 96.061 (252.3178, 136.6310, 56.1831) 32.3250 161.5426 10 89.457 (16.6216, 114.3987, 24.8565) 751.1315 673.5127 11 69.564 (300.5545, 6.3669, 47.3680) 0.0586 0.2046 12 107.647 (212.2843, 126.1011, 310.3013) 0.8405 0.8405 16

17. SHG power for both X and Y polarization 17 Graph shows that the variation of SHG power depend on the grain size as well as euler angle of each grain

18. Statistic data of sample (b) and output power SL n0. Grain diameter(micrometer) Euler Angle-Roe(degree) (θ, Φ , ψ ) SHG power(GW) For X-polarization SHG power(GW) For Y-polarization 1 104.3665 (252.1926, 123.3116 , 125.215) 66.1713 5.4893 2 93.83445 (358.8566, 58.574, 298.048) 1.2693 1.6503 3 90.63232 (108.9147, 115.2516, 5.756) 7.8047 412.8237 4 86.78514 (337.7185, 60.290376, 16.0723) 33.2678 586.3296 5 97.00452 (195.9331, 119.9577, 138.6314) 33.4438 58.9085 6 74.37478 (195.5058, 100.6249, 275.092) 7.6344 91.4245 7 93.02359 (288.4981, 44.5054, 212.1409) 799.9117 128.7787 8 102.2355 (262.1158, 61.2649, 229.3104) 1543.9 119.8417 9 101.5556 (252.3178, 136.6310, 56.1831) 0.7067 3.5318 10 97.80928 (16.6216, 114.3987, 24.8565) 494.8351 443.7009 11 80.49718 (300.5545, 6.3669, 47.3680) 737.8444 2576.3 12 98.65429 (212.2843, 126.1011, 310.3013) 116.5443 116.5443 18

19. SHG power for both X and Y polarisation 19 Graph shows that the variation of SHG power depend on the grain size as well as e uler angle of each grain

20. Statistic data of sample (c) and output power SL n0. Grain diameter(micrometer) Euler Angle-Roe(degree) (θ, Φ , ψ ) SHG power(GW) For X-polarization SHG power(GW) For Y-polarization 1 99.10493 (252.1926, 123.3116, 125.215) 185.0068 15.3473 2 95.17992 (358.8566, 58.574, 298.048) 4.6981 6.1084 3 78.24530 (108.9147, 115.2516, 5.756) 18.0109 952.6768 4 72.73445 (337.7185, 60.290376, 16.0723) 0.9998 17.6207 5 116.8323 (195.9331, 119.9577, 138.6314) 69.9681 123.2430 6 71.32447 (195.5058, 100.6249, 275.092) 8.8279 105.7172 7 88.37587 (288.4981, 44.5054, 212.1409) 0.2453 0.0395 8 104.5796 (262.1158, 61.2649, 229.3104) 706.1769 54.8140 9 102.2468 (252.3178, 136.6310, 56.1831) 7.0949 35.4564 10 99.07156 (16.6216, 114.3987, 24.8565) 130.0197 116.5840 11 75.02931 (300.5545, 6.3669, 47.3680) 0.3516 1.2276 12 96.22663 (212.2843, 126.1011, 310.3013) 0.3359 0.3359 20

21. SHG power for both X and Y polarization 21 Graph shows that the variation of SHG power depend on the grain size as well as euler angle of each grain

22. Future Work In future I will calculate and observe the variance of SHG power with changing the mean and standard deviation respectively as well as sphericity . Also changing the input wavelength to study the details variation of SHG. I will also change the material to obtain SHG like CdTe , ZnS . 22

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