Created by sebastien.popoff on 20/07/2013

Talks Wavefront shaping

 

Wavefront shaping: Controlling light in disordered materials

ANP2010 - Elbert van Putten
2010


See full post
Created by sebastien.popoff on 16/07/2013

Talks Wavefront shaping

Spatio-temporal control of light in complex media

PhD defense Sébastien Popoff

December 14th 2011


See full post
Created by sebastien.popoff on 15/07/2013

Highlights

Control of random lasing by wavefront shaping of the pump

[N. Bachelard et al., Phys. Rev. Lett., 109, (2012)]

[M. Leonetti et al., Appl. Phys. Lett., 102, (2013)]

[N. Bachelard et al., arXiv, 1303.1398, (2013)]

[T. Hirsch et al., Phys. Rev. Lett., 111, (2013)]

 

While conventional lasers use mirrors to confine light in a cavity with gain to achieve spontaneous emission, random lasers take advantage of multiple scattering to trap light in a disordered medium [1]. Such lasers do not require to carefully tune the geometry of the cavity, which greatly simplifies their design. They are potentially cheaper and more robust in the presence of perturbations (temperature, vibration). The resulting emission spectrums and radiation patterns are broad but mainly uncontrolled. In recent studies [2-5] different groups demonstrated numerically and experimentally the modulation of the spatial profile of the pump to control the spectrum [2-4] or the emission pattern [5].

See full post
Created by sebastien.popoff on 20/06/2013

Tutorials Spatial Light Modulators

How to use a binary amplitude Deformable Mirror Device (DMD) as a phase modulator: The Lee hologram method

 

 

The optical field measured at the output of a complex medium (multimode waveguide, multimode cavity, scattering medium...) is the result of the interference of the many paths taken by the light. Most of the applications of wavefront shaping techniques in these media rely on taking advantage of these interference effects to force the medium to perform a desired function. For this reason, the phases of the controlled segments of the input wavefront are usually the most important degrees of freedom to control. Common phase-only Spatial Light Modulators (SLMs) have a limited refresh rate (~100 Hz) due to the liquid crystal technology. This limits the applications in media with a low decorrelation time (like biological tissues) or for experiments for which a long optimization process is needed. Although a new class of phase-only SLMs based on deformable mirrors allows high-speed modulations (>30 kHz), these devices are currently very expensive compared to liquid crystal technology and have a limited resolution (~1000 pixels maximum). On the other hand, fast binary-amplitude modulators with high resolutions are widespread and affordable since the technology is the same one as used in commercial digital projectors. In a recent publication, [D.B. Conkey et al., Opt. Express (2012)] introduced a method to use such a binary-amplitude Deformable Mirror Device (DMD) for phase modulation. This technique allows a fast phase modulation (up to 23 kHz) at the cost of a loss of resolution.

See full post