Fluctuations in photon local delay time and their relation to phase spectra in random media

The temporal evolution of microwave pulses transmitted through random dielectric samples is obtained from the Fourier transform of field spectra. Large fluctuations are found in the local or single-channel delay time, which is the first temporal moment of the transmitted pulse at a point in the output speckle pattern. Both positive and negative values of the local delay time are observed. The widest distribution is found at low-intensity values near a phase singularity in the transmitted speckle pattern. In the limit of long duration, narrow-bandwidth incident pulses, the single-channel delay time equals the spectral derivative of the phase of the transmitted field.