51 lines
1.4 KiB
Matlab
51 lines
1.4 KiB
Matlab
clc
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clear
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%% User choices %%
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lambda = 1; % wavelength in um
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N = 2^10; % number of points
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Lz = 600; % z-limit of visualization in um
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Lx = 600; % x-limit of visualization in um
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r = 50; % radius of the beam in um
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l_start = 150; % z-coordinate of the input surface of the lens
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l_end = 250; % z-coordinate of the output surface of the lens
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p = 0.01; % parameter of the lens
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%%%%%
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k0 = 2 * pi / lambda; % wavenumber
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dz = Lz / (N - 1);
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dx = Lx / (N - 1);
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dkx = 2 * pi / Lx;
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z = 0:dz:Lz;
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x = -Lx/2:dx:Lx/2;
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kx = -pi/dx:dkx:pi/dx;
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E = exp(-(x / r).^2); % Gaussian beam
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% E = rect(x / (2 * r)); % uniform beam
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l_width = l_end - l_start; % width of the gradient lens
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dn = @(x, z) -0.5 * p^2 * x.^2 * rect((z - l_start - (l_width / 2)) / l_width); % function of the GRIN lens
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I = zeros(N, N); % resulting intensity
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for n = 1:N
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E = exp(-1i * k0 * dn(x, dz * n) * dz) .* ifft(fftshift(exp(-1i * sqrt(k0^2 - kx.^2) * dz) .* fftshift(fft(E))));
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I(n, :) = abs(E);
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end
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figure
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imagesc(z, x, rot90(I))
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colorbar
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title(sprintf("Beam radius = %.1f {\\mu}m. Lens start = %.1f {\\mu}m. Lens end = %.1f {\\mu}m. Lens parameter = %.3f", r, l_start, l_end, p))
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xlabel("z, mm")
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ylabel("x, mm")
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line([l_start l_start], [-Lx/2 Lx/2], 'Color','red','LineStyle','--');
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line([l_end l_end], [-Lx/2 Lx/2], 'Color','red','LineStyle','--');
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% colormap(gray) |