48 lines
1.3 KiB
Matlab
48 lines
1.3 KiB
Matlab
close all
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clear
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format compact
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clc
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% These calculations are based on Ashkin's article "Forces of a single-beam
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% gradient laser trap on a dielectric sphere in the ray optics regime
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%all distances in mm
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a = 1.0e-6; % radius of the bead
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n1 = 1.0; % index of rafraction of the medium
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n = 1.4607; % n2/n1
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n2 = n*n1; % index of refraction of the fused silica
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c0 = 3e8; % speed of light
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%reflectivity
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R = @(th,psi) (tan(th-asin(n1/n2*sin(th))).^2./...
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tan(th+asin(n1/n2*sin(th))).^2).*cos(psi).^2+...
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(sin(th-asin(n1/n2*sin(th))).^2./...
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sin(th+asin(n1/n2*sin(th))).^2).*sin(psi).^2;
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%transparency
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T = @(th,psi) 1-R(th,psi);
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r = @(th) asin(n1/n2*sin(th));
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% Factors
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Qs = @(th, psi) 1 + R(th, psi) .* cos(2*th) - T(th,psi).^2 .* (cos(2*th -...
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2*r(th)) + R(th, psi) .* cos(2*th)) ./ (1 + R(th,psi).^2 +...
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2*R(th,psi) .* cos(2*r(th)));
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Qg = @(th, psi) R(th, psi) .* sin(2*th) - T(th,psi).^2 .* (sin(2*th -...
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2*r(th)) + R(th, psi) .* sin(2*th)) ./ (1 + R(th,psi).^2 +...
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2*R(th,psi) .* cos(2*r(th)));
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Qmag = @(th, psi) sqrt(Qs(th, psi).^2 + Qg(th, psi).^2);
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t = linspace(0, pi/2, 1000);
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t_deg = t*180/pi;
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pol = pi/4;
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figure
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plot(t_deg, Qs(t, pol),'r--', t_deg, -Qg(t, pol),'b-.', t_deg, Qmag(t, pol),'k');
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grid
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xlabel('\theta, deg')
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ylabel('Q')
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legend('Q_s','Q_g','Q_t','location','northwest')
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sdf('my') |