Blinking the Fringes, Initial Development and Results of the Ultra-Low Speed Optical Chopper for the Self-Coherent Camera

Optical chopping is a step taken to acquire calibrated images for high-contrast instruments such as our SPIDERS pathfinder, the CAL2.0 Gemini Planet Imager 2.0 upgrade, and other future projects. A unique design with smooth, continuous, and slow operation is needed to blink the fringed and unfringed images for dim and bright stars. The Ultra-Low Speed Optical Chopper (ULSOC) must blink between 0.05Hz and 100Hz with noise-free operation, stop in the on or off position, and have its timing controlled by an external trigger. Silicone dampers are utilized to ensure it is vibration-isolated from other components in the system. The self-calibrating system accepts any chopping wheel between 10-30 blades without the need to reconfigure software and will find its home position on every power-up. The ULSOC communicates serially to start and stop as needed during operation. Long operational periods (during on-sky observations) over a lifetime of at least 10 years, closed-loop stepper-servo control and optical feedback from the chopper wheel guarantees accurate and repeatable velocity and position. Initial prototypes show that smooth and noise-free operation are possible for the desired speed ranges, and vibration is well-managed. Further development this year will lead to a fully functional device to be tested on-sky with our SPIDERS instrument and lead the way to revisions down the road for future projects.