Control of Light Transmission through Opaque Scattering Media in Space and Time

We report the first experimental demonstration of combined spatial and temporal control of light transmission through opaque media. This control is achieved by solely manipulating spatial degrees of freedom of the incident wave front. As an application, we demonstrate that the present approach is capable of forming bandwidth-limited ultrashort pulses from the otherwise randomly transmitted light with a controllable interaction time of the pulses with the medium. Our approach provides a new tool for fundamental studies of light propagation in complex media and has the potential for applications for coherent control, sensing and imaging in nano- and biophotonics.

Figure 1

Experimental setup (see text).

Figure 2

Optimized and random speckle pulses. (a) Amplitude of heterodyne signal of a nonoptimized pulse as a function of time delay, averaged over 50 random speckle pulses. (b) Typical single random speckle pulse. (c)–(g) Amplitudes of single pulses after optimization at different time delays which are indicated by the dashed arrows. The optimization has been performed by dividing the SLM into 300 segments. The optimization generates strong, short pulses from diffuse light. The zero delay position is at the maximum amplitude with no sample. The plotted curves have been normalized to the maximum of the average nonoptimized heterodyne signal (factor $1.53{\mathrm{mV}}^{-1}$).

Figure 3

Enhancement $\alpha$ versus selected time delay ${\tau }_{\mathrm{opt}}$ for different number of segments $N$ on the spatial light modulator.

Figure 4

Average amplitude enhancement $\alpha$ (dots) as a function of the square root of the number of segments $N$. The solid line is given by the expected $\alpha =0.90(\frac{\pi }{4}N{)}^{1/2}$, without any free parameter.

Figure 5

Detailed cross-correlation scans after optimization with $N=300$ segments around the time delays ${\tau }_{\mathrm{opt}}=1.1\mathrm{ps}$ (a), 4.8 ps (b), and 8.5 ps (c), together with a Gaussian fit (solid lines). The width (FWHM) of the peaks shows no significant dependence on the time delay, with an average of $\Delta {\tau }_{\mathrm{opt}}=(190\pm 7)\mathrm{fs}$.