Optical Alignment

The alignment of Horiba's Raman filter is difficult because it also acts as 
a beamsplitter. I think I have read somewhere that this "injection/rejection" 
configuration was good for seeing below 100cm^-1. 

There are a few adjustments that affect the alignment of this notch filter:

The filter is seated in its rotating cell with spring clips and four hex
screws that will move its position in the cell; effectively rotating the
filter horizontally and vertically.

The filter cell itself rotates horizonatally to a much larger extent.

The laser beam is directed by a right angle mirror into an offset mirror. 

The offset mirror angles the beam towards the Raman filter.
I suspect my mistake was thinking that the beam should hit this mirror 
over it's pivot. I didn't consider at that time that the pivot 
was offset from the center of the mirror. It occured to me
later that this offset was intentional and the beam should 
be allowed to hit that mirror further out. In doing so I was
then able to get the Raman filter to operate as expected.
Up until that point I was confused: why would the filter not
operate simultaneously as a Raman filter and as a beamsplitter?

An additional problem: the offset mirror has to be rotated to 
the most compressed limit of the spring that pulls the mirror
onto its set-screw. The spring is barely useful at that point
suggesting to me that the Raman filter may have degraded and
its operating angle has moved past the range of the mechanical
adjustments. Solution: get a new filter, or alter/replace the 
mechanical mounts so that the optics is correctly aligned.
[replaced the spring with a smaller spring. Later extended the 
offset mirror (which made using turret impossible).].