Fast Flash, Gating Image Through Turbid Media

Experiments by a team at the City College of the City University of New York indicate that the direct optical imaging of objects through scattering media may be improved with the use of ultrashort illumination and time gating. The findings may have an impact on lidar-based remote sensing and underwater surveillance, and on biological imaging.

As described in the Jan. 3 issue of Applied Physics Letters, the work involved variants of laser range gating, which commonly employs nanosecond-long pulses of 532-nm light from a Q-switched Nd:YAG laser and gating times of a similar duration.

The scientists instead used a Ti:sapphire oscillator and amplifier system to produce 130-fs and 3.5-ns pulses of 800-nm radiation, and they set the time gate of their intensified camera system for 80 or 500 ps. Images of a 1.41-lp/mm resolution target thus were collected through a suspension of 500-nm TiO₂ particles in water in four combinations of illumination and gate durations.

The highest resolution image was obtained with 130-fs illumination and an 80-ps gate width, centered on the time of the returning ballistic signal.