Wire grid polarizer dimension Why should the space between the wires be less than the wavelength of radiation in order for the polarizer to work efficiently?
 A: I will provide a heuristic interpretation of what is happening.
Taking a classical view of the electromagnetic field. For the wire grid polarizer any incident electromagnetic wave's electric field can be decomposed into a component perpendicular to the wires and parallel to the wires. For a wire grid polarizer you are counting on the grid to transmit the perpendicular polarization and reflect or absorb the parallel polarization.
The polarization perpendicular to the wires should be transmitted regardless of the spacing given that the wires themselves have a small enough diameter. This is because currents cannot be excited orthogonal to the wires so this component of the electric field won't interact strongly with the polarizer.
For the component that is polarized parallel to the wires, currents will be excited and the field will interact with the wires. The forward scattered fields of the current will cancel the incident field and the reverse scattered fields will show up as the reflected field. How strongly the field interacts with the polarizer as a whole depends on the spacing of the wires though. 
If you consider the gaps in the wires independently then they appear like apertures. With an aperture larger than a wavelength significant diffraction will occur and the parallel polarization will leak through. Increasing the transmitted power of the parallel polarized field. Noting that the transmitted fields power is proportional $T$ where, $T=1-|\Gamma|^2$. If $T$ increases then $|\Gamma|$ has decreased so less of the parallel polarized field has been reflected. Therefore, if you want to efficiently polarize the field the wire grid should have a spacing less than a wavelength to limit the amount of the parallel polarized field that diffracts through.
