OAP Alignment Using a LUPI
The LUPI-II Interferometer System simplifies the fine tuning of an OAP's (Off Axis Parabola) alignment. The equipment necessary is a vibration-isolated work area, LUPI-II, and an optical flat with a mount. Ideally the Flat should be as large as the OAP.
LUPI Setup. Locate the focus position of the OAP utilizing the MMOA Series Mount Reference Flat. Position the LUPI-II objective at the predetermined focus position of the OAP. Replace the Alignment Telescope with the Optical Flat.
LUPI Rough Alignment. Rough alignment is easiest in the spot of the LUPI-II. Align the LUPI's test beam focus, as it returns from the OAP and Flat, with the reference beam focus. Use only tip/tilt of the Optical Flat and focus of the LUPI-II.
Optimizing the OAP spot. The probable starting shape of the OAP focus is a skewed, elongated spot. A skew occurs by vertical misalignment of the focus position caused by the LUPI-II not being at the proper height relative to the OAP's radial axis. The elongated shape identifies off-axis alignment error, due to the LUPI-II focus not being at the proper OAD (Off Axis Distance) from the OAP.
Final Alignment. Focus the LUPI-II on the OAP and unblock the reference beam. Fine tune the system by observing both the horizontal and vertical fringes. Vertical misalignment is represented by the left/right asymmetry or fanning of the horizontal fringe pattern. Off axis misalignment is represented by a curved fringe pattern. When both are optimized, the OAP has been fully aligned.
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