Dual parallel X axis scale

Hi guys, please help review the script below.

I am making a plot with a dual x-axis (in nm and cm-1). The goal is to make a plot of Intensity vs wavelength in nm but at the same time have the wavelength scale in wavenumber parallel to each other. With my current script, the axes doesn't correspond well, for example: 2500nm correspoonds to 4000 cm-1 but what I got doesn't corresponds to this. See image below.

#script

wavenumber = 1e7 ./ wv11;

figure;

plot(wv11, miroptimized(2:end-1,:)); % Plot intensity vs wavelength

xlabel('Wavelength (nm)');

ylabel('Intensity');

ax2 = axes('Position', get(gca, 'Position')+[0, -0.03, 0, 0], 'Color', 'none', 'YTick', [], 'XAxisLocation', 'bottom', 'XLim', [min(wv11), max(wv11)], 'NextPlot', 'add');

xlabel(ax2, 'Wavenumber (cm^{-1})');

ax2.XLim = [min(wavenumber), max(wavenumber)];

ax2.Position = get(gca, 'Position')+[0, -0.03, 0, 0];

set(gca, 'Box', 'off', 'Color', 'none');

set(ax2, 'Box', 'off');