Alignment sensitivity of a WR-3.4 band quasioptical system for corneal water content sensing

A key barrier to clinical translation of THz reflection spectroscopy for corneal sensing is alignment sensitivity. Typical quasioptical systems are optimized for ideal alignment conditions and are thus not robust to errors in position between the focused wave front and corneal surface. Patient eyes are under continuous movement and, therefore, it is necessary to understand measurement fidelity degradation under cases of poor alignment. These issues are explored, via physical-optics simulations and experiments, for a two-lens quasioptical system operating in the WR-3.4 band. The misalignment tolerance is stricter on the optical axis than on the transverse plane. A 0.1 mm misalignment on the optical axis results in significant thickness and the water content measurement uncertainty and suggest an adjunct alignment verification system is necessary for clinical translation.