THORLABS OTKB/M User Manual page 11

Modular Optical Tweezers Chapter 5: System Setup
Remove the alignment cage plate and put the cage rod back to its original position. Combine the two pieces of the
beam expander segment again and use the remaining clamps to fix the beam expander segment in place.
Open the filter cube by pulling off the top piece and remove the cap on the back side of the cube. Be careful not to
touch the optics which are premounted in the cube. Use an IR viewing card (VRC5, included with laser segment
bag) to check the collimation of the laser beam. The collimation can be optimized by adjusting the distance between
the two lenses in the beam expander segment. To allow such adjustment the cage rods between Mirror 1 and the
dichroic filter holder do not go all the way through, but are rather connecting the two elements via cage plates where
two rods connect to one elements and the other two elements connect to the second element. The first beam
expander lens is located in the lens tube assembly after the first right angle mirror mount. Afterwards put the filter
cube and the cap back in place to close the filter cube.
Finally connect two 6" long cage rods (included in laser segment bag) to the right angle mirror mount at the trap
port, see Figure 6. Two irises are used to align the beam. The irises used in this alignment steps are included in the
vertical segment. They are shipped mounted in their final location; iris 1 is located before the objective and iris 2
before the condenser in the vertical segment. Temporarily take those iris out of the vertical segment and use them
during this alignment step. Iris 1 should be used with the cage plate to which it is connected in the vertical segment,
i.e. simply take the iris with the cage plate out of the vertical segment and slide it onto the 6" rods used in this
alignment step. See Figure 7 for the iris positions in the vertical segment.
Figure 6 Checking the collimation after the beam expander.
Use a standard two point alignment procedure to center the beam: Close the iris closest to mirror 2 and use
adjusters on mirror one to maximize beam throughput. Open that iris and close the second one. Now use adjusters
for mirror 2 to maximize the light going through. Toggle back and forth two to three times and then check if you get
light through while both irises are almost entirely closed.
Rev N, August 17, 2018 Page 9