A laser beam is directed at a polarizing filter followed by a quarter wave plate and a mirror. The mirror reflects the beam back though the wave plate and polarizer and onto a projection screen. If the quarter wave plate is properly oriented the beam viewed at the projection screen will be severely attenuated.

On an optical rail, install the laser, the polarizer, the wave plate and a mirror in this order. All surfaces must be normal to the beam. Align the mirror so that the beam passes again through the wave plate and polarizer and then hits a screen. Note that if the laser is too powerful, attenuation may be hard to see since the optics may not be rated for the specific wavelength.

L0, L1

PIRA DCS 6H35.40