301 lines
8.6 KiB
Mathematica
301 lines
8.6 KiB
Mathematica
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%% Define a beam and visualize it propagating
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% Define "optical system" using matrices. For this first example, we will just use a free space propagation matrix, and let the beam propagate a distance
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w0 = 1E-3; % 1mm beam waist
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lam = 421E-9; % wavelength
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zR = Zr(w0, lam); % Rayleigh range in m
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z0 = 0; % location of waist in m
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syms d; % Define 'd' as a symbolic variable
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M = propagator(d);
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[R, w] = q1_inv_func(0, w0, lam, M); % Do all the ABCD and q-parameter math, and return the waist and radius of curvature functions
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plotResult(w, d, linspace(0,10))
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%% Add a lens to the system
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w0 = 1E-3; % 1mm beam waist
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lam = 421E-9; % wavelength
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zR = Zr(w0, lam); % Rayleigh range in m
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z0 = 0; % location of waist in m
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syms d; % Define 'd' as a symbolic variable
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M = matmultiplier(propagator(d), lens(.5), propagator(1));
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[R, w] = q1_inv_func(0, w0, lam, M);
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plotResult(w, d, linspace(0,1,50))
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%% Add another to make a beam expander, that enlarges the beam waist by a factor 5 and then collimates it
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w0 = 1E-3; % 1mm beam waist
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lam = 421E-9; % wavelength
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zR = Zr(w0, lam); % Rayleigh range in m
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z0 = 0; % location of waist in m
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expansion_factor = 5;
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syms d1 d2 d3 f1 f2
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M = matmultiplier(propagator(d3), lens(f2), propagator(d2), lens(f1), propagator(d1));
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[R, w] = q1_inv_func(0, w0, lam, M);
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% Substitute values into w
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w = subs(w, {d1, d3}, {1, 0});
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% Solve for f1
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f1_eq = solve(w - expansion_factor*w0 == 0, f1);
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f1_eq_subs = subs(f1_eq, d2, 1);
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% Convert solutions to numeric values
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f1_val_numeric = double(f1_eq_subs);
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fprintf('f1 = %.2f m or %.2f m, for a lens separation of 1 meter\n', f1_val_numeric(1), f1_val_numeric(2))
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for i = 1:length(f1_val_numeric)
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f1_val = f1_val_numeric(i);
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R = subs(R, {d1, d2, d3, f1}, {1, 1, 0, f1_val});
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f2_val = solve(1/R == 0, f2);
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fprintf('f2 = %.2f, for a collimated beam, 5x the original waist, after propagating 1m to the first lens of f1 = %.2f, and propagating another 1m to the second lens\n', double(f2_val), double(f1_val))
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end
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chosen_f1_val = f1_val_numeric(1);
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fprintf('Chosen f1 = %.2f m \n', chosen_f1_val)
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M = matmultiplier(propagator(d3), lens(f2_val), propagator(1), lens(chosen_f1_val), propagator(1));
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[R, w] = q1_inv_func(0, w0, lam, M);
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plotResult(w,d3)
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estimated_expansion_factor = subs(w, d3, 0)/ w0;
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fprintf('beam is w = %.2f x w0\n', double(estimated_expansion_factor))
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beam_size_change = ((subs(w,d3,10) - subs(w,d3,0)) / subs(w,d3,0)) * 100;
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fprintf('Over 10 m after second lens, beam changes by %.5f percent\n', double(beam_size_change))
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%% Function definitions
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% Input Ray parameter, i.e. height and angle
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function ret = ray(y, theta)
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% Parameters
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% ----------
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% y : float or integer in meters
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% The vertical height of a ray.
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% theta : float or integer in radians
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% The angle of divergence of the ray.
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%
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% Returns
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% -------
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% mat : 2x1 matrix
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% [
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% [y],
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% [theta]
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% ]
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ret = [y; theta];
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end
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% Ray Transfer Matrix for ideal lens with focal length f
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function ret = lens(f)
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% Parameters
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% ----------
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% f : float or integer in meters
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% Thin lens focal length in meters
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%
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% Returns
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% -------
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% mat : 2x2 matrix
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% [
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% [ 1, 0],
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% [-1/f, 1]
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% ]
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ret = [1, 0; -1/f, 1];
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end
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% Ray Transfer Matrix for propagation over a distance d
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function ret = propagator(d)
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% Parameters
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% ----------
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% d : float or integer
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% Distance light is propagating along the z-axis.
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%
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% Returns
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% -------
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% mat: 2x2 matrix
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% [
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% [1, d],
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% [0, 1]
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% ]
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ret = [1, d; 0, 1];
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end
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% Multiplying the matrices together. mat1 is the last matrix the light interacts with.
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function ret = matmultiplier(mat, varargin)
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% Parameters
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% ----------
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% mat1 : 2x2 ABCD matrix
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% Last matrix light interacts with.
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% varargin : 2x2 ABCD matrices
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% From left to right, the matrices should be entered such that the leftmost matrix interacts
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% with light temporally after the rightmost matrix.
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%
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% Returns
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% -------
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% Mat : 2x2 matrix
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% The ABCD matrix describing the whole optical system.
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ret = mat;
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for i = 1:length(varargin)
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ret = ret * varargin{i};
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end
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end
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% Adding Gaussian beam parameters
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function zr = Zr(wo, lam)
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% Parameters
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% ----------
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% wo : float or integer
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% Beam waist radius in meters.
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% lam : float or integer
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% Wavelength of light in meters.
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%
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% Returns
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% -------
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% zr : float or integer
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% Rayleigh range for given beam waist and wavelength.
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zr = pi * wo^2 / lam;
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end
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% Calculate beam waist radius
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function w0 = W0(zr, lam)
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% Parameters
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% ----------
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% zr : float or integer
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% Rayleigh range in meters.
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% lam : float or integer
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% Wavelength of light in meters.
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%
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% Returns
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% -------
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% w0 : float or integer
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% Beam waist radius in meters.
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w0 = sqrt(lam * zr / pi);
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end
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function [z_out, zr_out] = q1_func(z, w0, lam, mat)
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% Parameters
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% ----------
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% z : float or integer
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% Position of the beam waist in meters.
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% w0 : float or integer
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% Radial waist size in meters (of the embedded Gaussian, i.e. W0/M).
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% lam : float or integer
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% Wavelength of light in meters.
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% mat : 2x2 matrix
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% The ABCD matrix describing the optical system.
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%
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% Returns
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% -------
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% z_out : float or integer
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% Position of the beam waist after the optical system.
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% zr_out : float or integer
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% Rayleigh range of the beam after the optical system.
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A = mat(1, 1);
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B = mat(1, 2);
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C = mat(2, 1);
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D = mat(2, 2);
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% Calculate Rayleigh range for the given beam waist and wavelength
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zr = Zr(w0, lam);
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% Calculate real and imaginary parts
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real_part = (A * C * (z^2 + zr^2) + z * (A * D + B * C) + B * D) / (C^2 * (z^2 + zr^2) + 2 * C * D * z + D^2);
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imag_part = (zr * (A * D - B * C)) / (C^2 * (z^2 + zr^2) + 2 * C * D * z + D^2);
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% Output the new position and Rayleigh range
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z_out = real_part;
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zr_out = imag_part;
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end
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function [R, w] = q1_inv_func(z, w0, lam, mat)
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% Parameters
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% ----------
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% z : float or integer
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% Position of the beam waist in meters.
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% w0 : float or integer
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% Radial waist size in meters (of the embedded Gaussian, i.e. W0/M).
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% lam : float or integer
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% Wavelength of light in meters.
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% mat : 2x2 matrix
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% The ABCD matrix describing the optical system.
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%
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% Returns
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% -------
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% R : float or integer
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% Radius of curvature of the wavefront in meters.
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% w : float or integer
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% Radius of the beam in meters.
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A = mat(1, 1);
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B = mat(1, 2);
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C = mat(2, 1);
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D = mat(2, 2);
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% Calculate Rayleigh range for the given beam waist and wavelength
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zr = Zr(w0, lam);
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% Calculate real and imaginary parts
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real_part = (A * C * (z^2 + zr^2) + z * (A * D + B * C) + B * D) / (A^2 * (z^2 + zr^2) + 2 * A * B * z + B^2);
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imag_part = -zr * ((A * D) - (B * C)) / (A^2 * (z^2 + zr^2) + (2 * A * B * z) + B^2);
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% Calculate radius of curvature and beam radius
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R = 1/real_part;
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w = sqrt(-lam / imag_part / pi);
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end
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function plotResult(func, var, rang)
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% Parameters
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% ----------
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% func : symfun (symbolic function of one variable)
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% Symbolic function defining the beam width after the last optical element.
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% var : symbolic variable
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% Variable in func that will be plotted.
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% rang : array (optional)
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% Array of values along the optical axis to be plotted. Default range is 0 to 3 with step size 0.01.
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% Set default range if not provided
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if nargin < 3
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rang = 0:0.01:3;
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end
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% Create a numeric function from the symbolic function
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func_handle = matlabFunction(func, 'Vars', var);
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% Compute the values of the function and its negative
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y_vals = func_handle(rang) * 1E3; % in mm
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y_neg_vals = -y_vals;
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% Create a figure
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figure;
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set(gcf, 'Position', [100 100 950 750]);
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% Plot the function and its negative
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plot(rang, y_vals, 'b'); hold on;
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plot(rang, y_neg_vals, 'b');
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% Fill the area between the curves with translucent blue color
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fill([rang, fliplr(rang)], [y_vals, fliplr(y_neg_vals)], 'b', 'FaceAlpha', 0.2, 'EdgeColor', 'none');
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% Add grid and labels
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grid on;
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xlabel('Optical Axis (m)', 'FontSize', 16);
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ylabel('Beam size (mm)', 'FontSize', 16);
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end
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