D = [0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0];
y = [0.022, 0.022, 0.030, 0.032, 0.037, 0.044, 0.059, 0.034, 0.052, 0.058, 0.061, 0.059, 0.062, 0.081, 0.085, 0.075];
lambdaD = 650e-9 * D;

p = polyfit(y,lambdaD,1);
plot(y,polyval(p,y), 'r-');
hold on;
plot(y,lambdaD,'ko');
h = legend ('numerical fit', 'Data', 'location', 'southeast');
set (h, "fontsize", 16);
xlabel('y (m)', 'FontSize', 16)
ylabel('\lambda D (m^2)', 'FontSize', 16)
axis('tight')
set(gca,'FontSize',16)