The 3 components described above secured together can be
considered as a Raman head restricted to one laser wavelength. If
the laser line is to be changed, then this head should also be
replaced or adapted with new optical parts. The head can be easily
removed from the microscope as both end components have the Olympus
mechanical connectors. Even if the height of this head is outside
the specification of Olympus for the maximum thickness of the
accessories which can be introduced into the microscope column, I have
not noticed any important image degradation. Of course for critical
imaging or quality photographs, it would be best to remove this
Raman head from the microscope. The telescope flip mirror has been
modify by removing first the mirror positioned on the rotating
plate (4), drilling a large hole
in that plate and holding the beam splitter in place with a
plastic sheet and screws. The precise angle between the splitter
and the laser beam can be adjusted with the blocking screw
(8). The adjustment of the angle
between the dichroic mirror and the laser beam is done by monitoring the
transmitted laser line which must reach a minimum for proper
positioning. If a classical beam splitter is used, its positioning
is not so critical but much light power is lost: 50% of the light
will be lost on each passage through the splitter it means that for
two crossings, 75 % of the light is lost. The beam splitter
can easily been swung out of the light path to get a full color
image of the specimen. The spectral curve of the dichroic plate from
http://www.edmundoptics.com/products/ is reproduced below.
Above the beam splitter, we can see the removable laser long pass
filter (7) to avoid the high
intensity laser line reaching the detector. This filter is removed
from the light path when adjustment of the optics is necessary ( for
instance positioning of the laser spot on the entrance slit of the
spectrograph ) or for image examination.