Delay in light transmission through small apertures

We demonstrate a technique for measuring pulse propagation time delays with 0.5-fs resolution by use of a widely available 100-fs pulsed laser. Using this technique, we measured the time delay of a light pulse transiting through subwavelength apertures placed on a $0.3‐\mu \mathrm{m}$ metallic film. We measured a 7-fs total transit time, corresponding to an effective group velocity of $c/7$. The experimental result yielded additional evidence that light interacts resonantly with oscillators formed by the surface modes near the small apertures.