Technology for Polarization Measurement

Optical Chopping (Intensity Modulation)

 

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

T4_2-1-9_A
Chopping frequency: PEM’s 2nd harmonic (2f)
 

Obtained Waveforms

T4_2-1-9_B

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.

Setup

Chopping frequency: PEM's first harmonic (1f)
 

Obtained Waveforms

 

APPLICATIONS

“Chopping” at tens of kHz without moving mechanical parts, vacuum UV to mid-IR
 

TYPICAL PEMs

I/FS50
II/ZS50
 

AVAILABLE INSTRUMENTATION

High Speed Optical Chopper
 

FURTHER READING

T. C. Oakberg and B. Wang, Application note - Light Intensity Modulation Using A PEM, Hinds Instruments, Inc. (1995).
 

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