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Fibre slit alignment

Two steps are required in order to align the fibre optic system. First, the slit and the prism are aligned together and, next, the slit - prism subset is aligned with the optical axis of the spectrograph.

The slit - prism alignment is conveniently performed in the laboratory. The focal plane bundle end is illuminated with a laser beam; the output light at the other end of the bundle enters the prism. The screws at the kinematic seats are adjusted in such a way that the output light from the slit does not become vignetted by the two slots of the prism holder.

In order to align the slit - prism set with the axis of the spectrograph, ISIS must not be mounted on the telescope. In this process, basically, the bundle slit must be aligned and centred on the detector, and also the optical axis of the central fibre of the bundle must be centred with the collimator's axis. The following steps are required:

The alignment process described up to now can be checked by means of a method which is similar to the autocollimation one. This method is as follows: a flat mirror is placed at the diffraction grating position, facing the collimator mirror -- the grating encoders position for the red arm to reach this situation is 35500. When a laser beam illuminates the focal plane end of one of the fibres at one slit edge, the output light is reflected by the collimator mirror. This beam will be reflected by the flat mirror and returned onto the collimator mirror, which will focus it (if the alignment is good) onto the opposite edge on the slit from where the light started.



Previous: Fibre slit mounting
Up: Installation and Setup for Fibre observing
Next: Guide fibre bundle focussing
Previous Page: Fibre slit mounting
Next Page: Guide fibre bundle focussing


Fri Jan 7 15:34:48 GMT 1994