Participants: Eleonora, Marc, Raffaele

Filter cavity mirrors are supposed to have a wedge of 400 urad. (See picture 1)

Since the wedge is not marked on the edge of the mirrors (as it happens usually), we had to measured it using an autocollimator. This tool works by projecting an image (a cross) onto the mirror and measuring the deflection of the returned image against a screen with a grid. If the mirror has a wedge, the reflection of the first and second surface are not superposed, resulting in two crosses on the screen. The line joining the crosses' center indicates the wedge direction (i.e the diameter with the maximum slope). It is not easy to precisely project the wedge line seen on the screen, on the mirror surface in order to glue the stand offs in the proper position (we want the wedge to be horizontal). In order to do this we used the following procedure:

1) We used as a reference a 4" spare mirror (used so far for gluing test) which as a marked wedge  (figure 2)

2) We put it on the glueing support and aligned the wedge with the stand off jig.

3) We moved the autocollimator in order to have the two crosses well aligned on an axis of the screen grid.

4) We replace the dummy mirror with the filter cavity mirror and rotate it in order to have the crossed aligned on the same axis as before. In this way the wedge should be aligned with the stand off glueing jig.

Since we can not distiguish the first and the second reflection of the mirror we don't know if the wedge is such that an impinging beam is reflected on the right or on the left.

We proceded glueing the magnets and stand-off. We glued the end mirror number 1 that, according to my simulation (see figure 4), is the best one to be used together with input mirror number 4.

We used a brand-new set of masterbond glue and we did all the work in the ATC clean room.

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We have measured a distance between the crossed of almost 2 division of the screen grid. We are not still sure 100% about how this data should be convert into a wedge value. Marc will report on it as soon as we find it out.