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 similar to 1 mu m, so that optimizing the system effective resolution (ER) requires choosing an operating wavelength below this limit. As an example, for 1-mu m 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 0.8 mu m, which generates an ER of 1.5 mu m (in air). The incorporation of additional bandwidth yields no ER improvement, due to uncompensated high-order dispersion and long-wavelength absorption. (C) 2005 Optical Society of America.