The effect of water dispersion and absorption on axial resolution in ultrahigh-resolution optical coherence tomography.

We examine the effects of dispersion and absorption in ultrahigh-resolution optical coherence tomography (OCT), particularly the necessity to compensate for high dispersion orders in order to narrow the axial point-spread function envelope. We present a numerical expansion in which the impact of the various dispersion orders is quantified; absorption effects are evaluated numerically. Assuming a Gaussian source spectrum (in the optical frequency domain), we focus on imaging through water as a first approximation to biological materials. Both dispersion and absorption are found to be most significant for wavelengths above ~ 1microm, so that optimizing the system effective resolution (ER) requires choosing an operating wavelength below this limit. As an example, for 1-microm source resolution (FWHM), and propagation through a 1-mm water cell, if up to third-order dispersion compensation is applied, then the optimal center wavelength is 0.8microm, which generates an ER of 1.5microm (in air). The incorporation of additional bandwidth yields no ER improvement, due to uncompensated high-order dispersion and long-wavelength absorption.