Fig 1. An illustration of the orientation and rotation of the QWP and HWP compared to the polarization of the incoming laser light.

The motors containing the QWP and HWP are not calibrated according to the x-axis. Therefore, a relative angle ϕ = ϕ′ − ϕ₀ and θ = θ′ − θ₀ have to be implemented for the QWP and HWP, respectively. Here ϕ′ and θ′ are the angles provided by the motors, and ϕ₀ and θ₀ are the angles of the fast axis of the QWP and HWP, respectively, compared to the x-axis when the motors are at 0°.