Imaging objects hidden in highly scattering media using femtosecond second-harmonic-generation cross-correlation time gating.

A combination of 100-fs cross-correlation time gating and lock-in amplifier detection is shown to be a versatile technique to image objects hidden in highly scattering media. The image is formed from the ballistic component of the ultrafast laser pulse while the diffuse component is eliminated by time gating using cross-correlation second-harmonic generation. The low-noise lock-in amplifier detection method and the high-repetition-rate milliwatt pulsed laser enable us to image through a random medium as thick as 28 scattering mean free paths with submillimeter resolution.