Weizmann Institute of ScienceRehovot, Israel

[1] Spatio-temporal X-wave, E.Small, O.Katz, Y.Eshel, D.Oron, Y.Silberberg, Opt.Exp. 17, 21, 18659 (2009)[2] Transformation from an ultrashort pulse to spatiotemporal speckle by a thin scattering surface, E.Tal and

Y.Silberberg, Opt. Lett. 31, 3529 (2006).[3] Focusing coherent light through opaque strongly scattering media, I.M.Vellkoop, A.P. Mosk, Opt. Lett.

32, 16, 2309 (2007).[4] Focusing and compression of ultrashort pulses through scattering media, O. Katz, Y. Bromberg,

E. Small, Y. Silberberg, arXiv:1012.0413 (2010).

Experimental results [4] Mechanism for temporal control & compression:

Perhaps counter-intuitively, temporal control is attainable using only spatial control. The underlying physics: much like a Fourier pulse-shaper, coherent random scattering couples the temporal and spatial degrees of freedom:

We show that correction of both spatial and temporal distortions of ultrashort pulses travelling through inhomogeneous media can be attained by wavefront shaping alone. Moreover, we demonstrate that by optimizing a nonlinear signal the refocused pulse can shorter than the input pulse, controlling only the spatial degrees of freedom. We apply our technique to spatioemporally focus 100fs pulses through thick bone and brain tissues.

Free space focusing Focusing through a thick scattering medium

Background: When an ultrashort pulse propagates through an inhomogeneous medium, scatterings distort the light field in both space and time, resulting in a spatiotemporal speckle [1,2], limiting optical focusing, imaging and manipulation:

zoom-in

Focusing through a thin scattering surface [1,2]

• A 2-D spatial light modulator (SLM) controls the incident wavefront [3].

• The wavefront is adaptively optimized for exciting a spot in a two-photon fluorescence (2PF) screen.

• An interferometer is utilized for spatially-resolved autocorrelation measurements, enabling full spatiotemporal characterization of the focused light field [4].

Experimental system

Controlling ultrashort pulses in scattering mediaOri Katz, Yaron Bromberg, Eran Small, and Yaron SilberbergDepartment of Physics of Complex Systems, Weizmann Institute of Science, Israel

SLM

2PF screen

10X 20X

EMCCD

F

scattering medium

femtosecond pulse

glass slab (optional)

Initial temporal width Optimized temporal width

z x

y

z x

y

x

y

Initial 2PF Optimized 2PF

x

y

x

y

x

y

nearly TL output

=

SLM#1#2

#3

Random-scattering pulse shaping:

#1

#2

#3

+

+

Temporal/spectral speckle basis

Standard frequency-domain pulse shaper:

SLM +

+=

Fourier/spectral basis

max

2PF autocorrelation