The magnetic bearing motor CM-AMB-400 with a chopper rotor is demonstrated in the video below. A laser beam (generated by a FP-Mini-520 from Laser Components) is cropped by a precision pinhole with an opening of 500 µm, then passes through the chopper and detected by a photodiode (ODD-1WB by Opto Diode). The current of the photodiode is amplified by a transimpedance amplifier and made visible with a digital oscilloscope.
At start, the rotor is lifted by the magnetic field and the angular position is controlled such that the laser beam can pass through one hole of the chopper rotor. The rotor is then turned by half of the angle between two holes and with that the laser beam is completely blocked. This feature is beneficial for setting up an experiment having a constant beam for aligning the beam path or blocking it, as a continuous beam could damage or destroy some parts of the experiment. Finally, the rotor speed is increased stepwise, and the chopped laser beam is visualized on the oscilloscope. With the motor shown in the video, chopper frequencies up to 200 kHz are possible within a vacuum of ≤ 1 mbara.
