Fast terahertz corneal imaging system with automatic motion compensation: application to in vivo mapping of hydration gradients

Terahertz time-domain spectroscopy (THz-TDS) hasshown strong potentialfornoncontact cornealhydration sensingand surface-profile metrology, but in vivo imaging remains challenging because the curved corneal surface requires precise phase matching and rapid acquisition to suppress motion artifacts. We report a fast single-pixel THz corneal imaging system that combineselectronically controlled opticalsampling (ECOPS) forkilohertz waveform acquisition with a direct-drive two-axis beam-steering mirror and a pair of custom hyperbolic-elliptical lenses optimized for wide-field spherical scanning.The system acquiresa 40°×40°field of view in 0.8 s (and 60°×60°in <3 s), enabling sub-second spectralimaging while maintaining the required wavefront curvature. To compensate for subject motion, we introduce an automatic alignment method that estimateslateraland axialmisalignment from the time-of-arrivalsurface profile and repositions the scannerusing three motorized translation axes.As a demonstration,we captured time-lapse THz images of a contact-lens corneal phantom during controlled drying and observed reproducible changes in the reflected waveform amplitude and shape consistent with the measured decrease in hydration. These results establish a practical route toward in vivo THz mapping of corneal hydration gradients with automated motion compensation.