2 4 6 8 10 10 GLYPH<Minus> 2 10 GLYPH<Minus> 1 10 0 10 1 GLYPH<CapDelta>Λ GLYPH<LParen1> nm GLYPH<RParen1> f D Fig. 5. (Color online) Theoretically-predicted best achievable fractional de- lay vs. input pulse bandwidth (centered at λ$_{c}$ ) subject to the constraint that D$_{a}$, D$_{p}$ < 0.05, which corresponds to negligible distortion ( i.e. , just noticeable upon visual inspection). To go beyond pulse broadening and quantify the potential impact of the propagation- induced intensity oscillations, we compute the power leakage, which is defined as the fraction of total pulse power extending beyond a temporal window encompassing the main part of the pulse. To calculate the power leakage, we first establish a temporal window to define the main pulse (this can be thought of as a channel in the context of information theoretic applications [25]). For our sinc pulses, we choose the window to be the time between the first minima surrounding the main pulse peak (before it passes through the vapor). We then adjust the center of this window until it contains the largest fraction of transmitted pulse power; the fraction of total pulse power outside this window is the leaked power. By using this metric, we gain insight into how higher order distortion contributes to spreading of the pulse beyond its initial channel. Figure 6 b) shows the power leakage for a 250-fs-long pulse with several different spectral profiles. We experimentally observe a power leakage of 65% for a fractional delay of 18 (corresponding to a vapor temperature of 294 ◦ C). We note that, for an undistorted sinc pulse, approximately 10% of the pulse power extends beyond the main pulse. Thus, although the broadening of the Gaussian and sinc pulses are comparable, the power leakage for the 11