Interferometric Measurement with Chopped Beam

This application note outlines a method to use SmarAct's PICOSCALE interferometer in setups where the optical path is periodically interrupted. This method is often needed in lock-in techniques, where standard interferometric readings of path lengths become complex due to the interruptions. The solution presented bypasses typical interferometric calculations and uses triggered raw data acquisition combined with post-processing to track displacement.

Problem: Optical chopping disrupts continuous interferometric readings, making standard position calculations invalid.

Solution:

• Use the PICOSCALE’s Advanced Trigger firmware to trigger raw data acquisition only when the beam path is clear.
• This process involves setting up synchronized clocks, one for triggering the chopper and another for triggering data extraction.

Implementation:

• The interferometer setup includes a chopper and data streaming configuration using triggers to synchronize data extraction with clear beam paths.
• A python script or GUI handles the post-processing to calculate positions based on the raw data captured during undisturbed intervals

Results: Tests show that the interferometer can track mirror displacement accurately, even when the beam is periodically chopped, provided the mirror does not move too quickly. The solution is demonstrated through experiments, showing consistent and reliable displacement tracking when the beam is chopped and compared with uninterrupted setups​.