Spatio-temporal focusing of an ultrafast pulse through a multiply scattering medium

Abstract

Pulses of light propagating through multiply scattering media undergo complex spatial and temporal distortions to form the familiar speckle pattern. There is much current interest in both the fundamental properties of speckles and the challenge of spatially and temporally refocusing behind scattering media. Here we report on the spatially and temporally resolved measurement of a speckle field produced by the propagation of an ultrafast optical pulse through a thick strongly scattering medium. By shaping the temporal profile of the pulse using a spectral phase filter, we demonstrate the spatially localized temporal recompression of the output speckle to the Fourier-limit duration, offering an optical analogue to time-reversal experiments in the acoustic regime. This approach shows that a multiply scattering medium can be put to profit for light manipulation at the femtosecond scale, and has a diverse range of potential applications that includes quantum control, biological imaging and photonics.

Controlling waves in space and time for imaging and focusing in complex media

“…This is now becoming possible thanks to recent advances on the spatiotemporal control of optical wave fields through random media [65][66][67] . Two of these demonstrations 65,66 relied on the optimization a pulse's peak intensity after it had propagated through a complex medium, either by heterodyne interferometry (Fig.…”

“…These results were an important development over the earlier work of Aeschlimann and colleagues 68 , who focused light onto plasmonic nanoparticles by employing a feedback-based optimization technique to polarization-shape a light pulse. In the third demonstration 67 , McCabe and colleagues directly measured the complex spectrum of the optical field at a point in space and then phase-shaped the light pulse such that it focused in space and time at the chosen location.…”

“…Current experiments [65][66][67] control either the frequency domain or the spatial domain, but not both. An optical TRM will open up an entirely new class of time-reversed optics experiments, yielding new fundamental insights into wave-scattering phenomena [22][23][24]27,121 .…”

Spatio-temporal characterization and control of ultrashort pulses through a multiply scattering medium

“…We measure the diffusion properties of the scattering sample [8]. Finally, inspired from time-reversal experiments and using spectral pulse shaping, we demonstrate the spatially localized temporal recompression of the output speckle to the Fourier-limit duration [9]. Our study branches out previous spatial-speckle shaping techniques to the temporal domain and bridges the gap with time-reversal experiments in acoustics and electromagnetism.…”

Minimum reflection channel in amplifying random media

“…Recent developments of wavefront shaping and phase recording techniques in optics have enabled the coupling of incident light to these open channels [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] . The open channels can greatly enhance light transmission through scattering media, having a profound impact in a wide range of applications from deep tissue imaging and laser surgery, to spectroscopy [20][21][22][23][24][25][26][27][28][29][30] and opto-genetics 31 . So far, most experimental studies of high transmission channels rely on optical access to both sides of a scattering media, which is not practical in realistic situations.…”