Date of Award

Fall 8-26-2026

Document Type

Thesis (Master's)

Department or Program

Physics and Astronomy

First Advisor

Kevin Wright

Second Advisor

Miles Blencowe

Third Advisor

Chandrasekhar Ramanathan

Abstract

This thesis develops a documented, reproducible procedure for building diffraction-limited microscope objectives entirely from catalog singlets, for imaging ultracold 6Li atoms in a ring-trap experiment. The objectives must resolve micron-scale features through a 5 mm fused-silica vacuum window, operate at multiple wavelengths, fit inside a 48 mm magnet bore, and contain no conductive or magnetic material, because the surrounding coils switch 0.1 T fields on microsecond timescales. Commercial long-working-distance objectives are universally housed in metal, which the eddy-current constraint rules out, and custom fabrication of a suitable non-conductive matched pair is estimated at nearly $200k.

The procedure is developed and validated on an existing five-element design used in the WrightLab since 2016: five N-BK7 singlets in a 1-inch barrel, with a numerical aperture of 0.30, an effective focal length of 33.65 mm, and a diffraction-limited field of view of ±0.55 mm through the window. Tolerance analysis of this design shows its performance is governed by a single surface, which must be centered to within about 22 µm of the common axis, an order of magnitude tighter than the clearance of a lens in its barrel. To meet this requirement, the objective was rebuilt in a 3D-printed barrel with radial adjusters, and each element was actively centered as it was placed, on a rotary bearing under a point source microscope, using the reflections from every accessible lens surface.

The rebuilt objective was validated against the laboratory's original assembly of the same design, both measured back-to-back on the same instrument. The new assembly is 1.5–7.8× better centered on every measured surface, and its critical surface sits at the instrument's noise floor of about 4 µm, five times inside the tolerance. Its measured point-spread function is 1.09 ± 0.02 by 1.07 ± 0.02 µm FWHM at 97% of the design aperture, in agreement with the 1.12–1.16 µm diffraction prediction, while the original assembly's spot is about 1.4× broader. The same procedure then assembled, without modification, an eight-element chromatically compensated design intended to replace the original. The alignment procedure, the calibration of the metrology, the reflection lookup tables that specify every measurement position in advance, and the acceptance criteria are all recorded here, so the laboratory can build, verify, or re-certify objectives of either design without rediscovering the process.

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