 Want both rays of light to enter crystal as s-state polarization. The polarizing beam splitter causes mostly s-state light to take the first path (which passes through the two s-polarizers) and p-state light to continue past the beam splitter. The presence of the two s-polarizers ensures that any p-state light taking that path is stamped out. The second half-waveplate converts from p- to s-state light. Both rays of light need to be parallel to each other as they approach the lens in order for the rays to intersect at the focal point of the lens. The crystal is placed at this focal point in order to basically halve the wavelength of the entering light; since the incident light is red, or somewhat under 800 nm, the light on the other side would have a wavelength closer to 400 nm, which makes the light appear blue. |
2nd half of set-up |