29-01-2021 #

First Nulling Trials #

In order to Validate some of our ideas on the coronagraph approach for RISTRETTO, we have first set-up a test bench trying to achieve good nulling contrast levels using a S-630-HP fiber, the one we have selected for the instrument.

*Microscope image of the PSF that was injected into the test fiber. There is still a large coma aberation. The color scale is logarithmic*

A PSF, has been produced, by a fiber test set-up with an F/4 beam (the optical quality was far from perfect). This allowed us to test some precise translation system and map the coupling of a fiber when wandering around the PSf.

coupling map — *Map of the coupling efficiency, when offseting the fiber position from the maximum. The red line is the cut that is shown on the figure below*

This way we showed that our measurement system and our test environment are stable enough to measure long term nulls. This is very encouraging !

nulling stability — Value of the normailized flux in the fiber along the red line in the above figure. The x axis is the time in seconds. Once arrived at position the null is meaintained to see its stability, and then the ligh is cut check that the null is really flux measured