pinhole placed at the center of the
cavity served as the target, simultaneously locking the phases and
frequencies of the modes that form
the lasing pattern.
We observed tight focusing of the
scattered lasing radiation through a
variety of scattering samples including
thin tissues and dynamic samples. 4
Our results show that focusing occurs
on sub-microsecond time scales
through self-organization by the laser
itself, without any external control or
manipulation. Thanks to this speed,
potential applications may be found
in free-space optical communication,
in the study of dynamic samples, and
in focusing through scattering layers
such as the skin.
The ability to control light through dynamically varying heterogeneous media could be important for
applications ranging from free-space
communication to laser therapy. The
underlying challenge is to control an
optical wavefront with a large number
of degrees-of-freedom (DOF) faster
than the medium dynamics. Recent
publications show exciting developments in the control of light in turbid
media by wavefront-shaping using
computer-controlled spatial light
modulators. 1–3 Unfortunately, these
techniques are fundamentally limited
by relatively slow response times. Consequently, high-resolution wavefront-shaping has not been demonstrated
in samples that evolve on millisecond
timescales, such as live biological
tissues or liquid suspensions.
We have demonstrated a novel all-optical wavefront-shaping approach
capable of generating a sharp focus
through turbid media at sub-microsecond time scales. 4 The approach
relies on the self-organization of the
optical field inside a multimode laser
cavity to find the optimal wavefront
that forms a sharp focus from the
otherwise randomly scattered light.
We achieved this by using a reflection
from a small retro-reflecting target
that is placed at the desired focal
plane, as all-optical feedback. This
feedback is used to initiate lasing
through the sample in a lasing-state
that focuses the maximum power on
the target. To ensure a large number
of DOF we used a unique self-imaging
laser cavity, which supports thousands of transverse modes. 4–5 A
(a) Experimental setup for wavefront shaping through scattering media by all-optical
feedback. The lasing pattern at the target plane is monitored by a camera. (b) Intensity
distribution at the target plane for conventional focusing. (c) Intensity distribution at
the target plane for the lasing pattern.
Micha Nixon, Ori Katz,
Asher A. Friesem,
Yaron Silberberg and
Nir Davidson (nir.davidson
Weizmann Institute of
Science, Rehovot, Israel
1. I.M. Vellekoop and A.P.
Mosk. Opt. Lett. 32, 2309
2. A.P. Mosk et al. Nature
Photon. 6, 283 (2012).
3. O. Katz et al. Nature
Photon. 6, 549 (2012).
4. M. Nixon et al. Nature
Photon. 7, 919 (2013).
5. M. Nixon et al. Phys. Rev.
Lett. 110, 184102 (2013).
Focused Lasing Through
Dynamic Scattering Media
Lasing pattern Conventional focusing
gain medium Lens