Optical Chopping

USING THE PEM’S 2F REFERENCE

The PEM modulates light polarization. When a PEM is used between two crossed polarizers, the set-up can modulate the intensity of a light beam (chopping). This intensity modulation is at a fixed frequency between 40 and 200 kHz.

Setup

Chopping frequency: PEM’s 2nd harmonic (2f)

Obtained Waveforms

USING THE PEM’S 1F REFERENCE

When the PEM is set up between a circular polarizer and a linear polarizer the following “on and off” chopped waveform is obtained. Note the obtained waveform approximates a 50/50 duty cycle. The extinction ratio is set by the extinction ratio of the polarizers used in the optical path.