The substrates of Zero phase reflectors are usually Silicon or OFHC Copper. In most laser machines, one or several Zero-Phase Reflectors are used to forward the laser beam from the cavity to the working head. At these mirrors, reflectance should be as high as possible in order to minimize loss of laser power. In addition, phase shift between the s- and p-polarized components of the reflected beam should be as low as possible in order to avoid disturbing the polarization of the laser beam.