Alignment

General Information

Beam height above table surface: 160 mm

Abbreviations

• SL - Scan lens
• Galvo - Galvanometer mirror
• VAT - Vertical alignment tool

Set Up

1. Ensure that the alignment laser is level with the table by checking its height at two separate, far apart locations on the bench.
2. Ensure that the alignment laser is collimated. Below is a table of wavefront radii of curvature at different distances from the laser as measured with a Shack-Hartmann wavefront sensor.
3. Set the alignment laser beam height to ~160 mm above the table surface.
4. Ensure that the galvanometer mirror is at that correct height above the table by carefully putting the alignment laser next to it and visually verifying that it would intercept the entire cross section of the beam.

Distance, cm	RoC, m
50 cm	-30 +/- 1
75 cm	-35 +/- 2
100 cm	-40 +/- 3

Excitation Path

Phase 1

Align Galvo and Scan Lenses 1 and 2

1. Set the galvanometer voltage to 0V
2. Put an adjustable ND filter in front of the laser beam.
3. Place two irises on a row of bolt holes on the table. Align the laser to them.
4. Insert the galvanometer mirror and place it so that the beam is roughly in the center of the mirror.
5. Use C-clamps to move the two irises after the mirror on a column of bolt holes. Position the galvanometer so that the beam passes through the irises at these new positions.
6. Close down both irises. Insert a mirror after the second iris and align the back reflected beam back through both irises.
7. Insert a coverslip after the ND filter to pick off the reflected beam.
8. Insert two new irises to define the path of the pick off beam. Their absolute position doesn't matter.
9. Insert scan lens one (SL1) and place it such that the distance between the mirror and the lens housing is approximately 170 mm. Use the speckle size from scattering from a white piece of paper to verify that the mirror is near or at focus.
10. Adjust positioning of SL1 until the pick off beam is recentered through the irises and the forward the beam goes through both irises. Forward and backward beams may not agree completely; this is OK. Align them as close as possible.
11. Insert SL2 and place it approximately 170 mm after the galvo. Align its transverse position so that the forward and backward beams pass through all irises.
12. Insert the Shack-Hartmann wavefront sensor after SL2. Adjust SL2's axial position until the output beam is collimated (absolute value of the radius of curvature is greater than about 30 m, the value of the beam's RoC directly out of the alignment laser).
13. Remove the wavefront sensor and iterate over the last two steps until transverse and axial alignments are good.

Align Objective and Tube Lens

1. Insert two mirrors after SL2 in a figure 4 configuration. Use two irises to align the beam into the 90 degree upward folding mirror. (One iris is on the mirror mount in the photos.)
2. Insert the vertical alignment tool (VAT) into the objective barrel. Use the tip/tilt adjustment screws on the folding mirror and adjust its position on the table until the beam is traveling approximately vertical and is centered along the axis where the objective will be placed. 2x tip/tilt adjusters and x/y positioning provide the full four degrees of freedom for beam positioning. You will not be able to exactly align the beam until the next step. Just make it approximate.
3. Remove the alignment disk from the lower cage plate on the VAT. Use the adjustment screws on the folding mirror to align the beam to the tool's iris at the far end of the tool. Insert the alignment disk. Use the adjustment screws on the mirror in the figure 4 assembly that is closest to the assembly to align the beam into the hole in the alignment disk. Iterate until good alignment through both irises is achieved.
4. Remove the VAT and insert the objective. If the beam exits the objective at an angle, adjust the folding mirror's position until the beam travels vertically.