Fiber slit test done for the first spectrograph module

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In this article, we are going to show recent news at Laboratoire d’Astrophysique de Marseille (LAM, France), where the first PFS Spectrograph module is being integrated.

The assemblies for the first spectrograph module, such as the visible-blue and red cameras, optical bench and optical components have been delivered to LAM, as we showed in the previous article. Since then, the fiber slit assembly has been delivered from Brazil, and LAM started integrating these assemblies into the entire spectrograph system.

The first step of the integration is to align the fiber slit and the optical component called collimator. The fiber slit is the spectrograph entrance of the light from the focal plane, where fibers catches the light of galaxies and stars. The lights from the sit are reflected at the collimator mirror and get parallel with each other (i.e. “collimated”). The below photo shows a snapshot of the alignment work. A dedicated telescope is used for the alignment.

Snapshot of the alignment of the fiber slit and the collimator. The small telescope on the right side is used for the alignment.

LAM team working for the alignment. 

In the middle of July 2018,  a member from Brazilian team visited LAM to test the optical performance of the fiber slit itself. At the test, a screen was located in front of the collimator assembly and a ring was made on the screen by illuminating one fiber. The ring width was measured to test the optical performance. We have improved the test procedure to obtain the test data efficiently and firmly.

Snapshots of the optical test of the fiber slit.
Left: at the test, we measure the ring width on the screen made by illuminating a fiber with the laser.
Right: Antonio Cesar Oliveira (LNA: Laboratório Nacional de Astrofísica) from the Brazilian team testing the fiber slit.

We have done the test successfully, and LAM have continued to finalize the slit alignment and then will proceed to the next step of the integration. Besides, at this test, we recognized a few things to be improved in the slit production process and to be tested in Brazil and checked at France. We are developing the PFS instrument with getting feedback to the integration processes for the next modules.