DIY Optical Isolation
- 1). Place the linear polarizer in the output beam of your laser. If your laser is linearly polarized, as many are, line the polarizer up with the output polarization of the laser. You can do this by monitoring the beam energy or intensity "downstream" of the linear polarizer as you rotate it. When the energy of the beam is maximum, you've matched the laser polarization.
- 2). Place the quarter-waveplate in the beam after the linear polarizer. The quarter waveplate has a fast axis and a slow axis. The waveplate slows down light polarized along its slow axis -- delaying or retarding it by a quarter wavelength relative to the fast axis.
- 3). Put a flat mirror in the beam after the quarter-waveplate. Adjust the mirror so you can see the reflected beam on the side of the linear polarizer closest to the laser. You can shine the reflected beam on the laser housing itself, or hold a piece of paper by the side of the output beam.
- 4). Rotate the quarter-waveplate while looking at the reflected beam. The beam will disappear when the waveplate is oriented to shift the polarization so the reflected beam can't make it back through the linear polarizer.