Fig. 5.

Point spread functions obtained at 7 different depth points when Δf = -2.5 MHz; (a) before and (b) after mapping to linear n-space. The degradation in signal power with depth is no more than 5 dB over the total depth span of 5.8 mm in (b), as opposed to an 11 dB degradation shown in Fig. 4(b) without the frequency shift.