Homemade set-up

Hello guys,

I am pretty new to this topic and not a physicist.

We have here a home build SPR set up and I need to study its construction, so I can build up one on my own in a different laboratory. This is part of my Master Thesis.

My problem is the laser beam it self. I am trying to make it paralel but once I add the prism, the laser beam falls down so that I can't use a collecting lense. The laser beam is moving and I can't make any measurements, since the beam moves and doesn't touch the detector at some angles.
I can see the plasmon (the laser beam disappears almost).
Anyone has an idea? Our set up looks somewhat like the picture

I just figured out the problem, you can delete this post.
Thank you