Weizmann Institute of Science Rehovot, Israel

1. Controlling ultrashort pulses in scattering media Ori Katz, Yaron Bromberg, Eran Small, and Yaron Silberberg Department of Physics of Complex Systems, Weizmann Institute of Science, Israel SLM = y y y x 2PF screen x x z z max Weizmann Institute of Science Rehovot, Israel EMCCD 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.  Temporal/spectral speckle basis glass slab (optional) F femtosecond pulse 10X SLM #1 scattering medium 20X + #2 + #3 zoom-in 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: Focusing through a thick scattering medium Focusing through a thin scattering surface [1,2] Free space focusing • 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 Mechanism for temporal control & compression: Experimental results [4] 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: Standard frequency-domain pulse shaper: Fourier/spectral basis Initial 2PF Optimized 2PF + y y y x x x + 2PF autocorrelation Random-scattering pulse shaping: Initial temporal width Optimized temporal width nearly TL output SLM #1 = #2 #3 [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).