650 GHz imaging as alignment verification for millimeter wave corneal reflectometry
Yong Hu (University of California)
Mariangela Baggio (Aalto University)
Shahab Dabironezare (TU Delft - Tera-Hertz Sensing)
Aleksi Tamminen (Aalto University)
Brandon Toy (University of California)
Juha Ala-laurinaho (Aalto University)
Elliot Brown (Wright State University)
Nuria Llombart (TU Delft - Tera-Hertz Sensing)
Sophie X. Deng (University of California)
Vincent Wallace (University of Western Australia)
Zachary D. Taylor (Aalto University)
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Abstract
A system concept for online alignment verification of millimeter-wave, corneal reflectometry is presented. The system utilizes beam scanning to generate magnitude-only reflectivity maps of the cornea at 650 GHz and compares these images to a precomputed/measured template map to confirm/reject sufficient alignment. A system utilizing five off-axis parabolic mirrors, a thin film beam splitter, and two-axis galvanometric mirror was designed, simulated, and evaluated with geometric and physical optics. Simulation results informed the construction of a demonstrator system which was tested with a reference reflector. Similarity metrics computed with the aligned template and 26 misaligned positions, distributed on a 0.5 mm x 0.5 mm x 0.5 mm mesh, demonstrated sufficient misalignment detection sensitivity in 23 out of 26 positions. The results show that positional accuracy on the order of 0.5 mm is possible using 0.462 mm wavelength radiation due to the perturbation of coupling efficiency via beam distortion and beam walk-off.