Wavefrontshaping: Controlling light in disordered materials

ANP2010 - Elbert van Putten

2010

 

 

Transcript:

 

Wave front shaping : 

Elbert van Putten Complex Photonic Systems Wave front shaping Controlling light in disordered materials

Acknowledgements : 

Acknowledgements Duygu Akbulut Ivo Vellekoop Allard Mosk Ad Lagendijk Willem Vos Photon Scattering Group (AMOLF, Amsterdam) Complex Photonic Systems

Light and Disorder : 

Light and Disorder Scattering obstructs view

Scattering is a nasty problem : 

Scattering is a nasty problem target Today I’ll show you that scattering can be extremely useful

Outline : 

Outline Scattering in optics Wave front shaping Focusing through opaque materials Focusing inside opaque materials

Speckle : 

Speckle - Light still interferes after it is scattered - Transmitted light has random phase: laser speckle - Low intensity, no resolution.

How to describe this scattering? : 

How to describe this scattering? See the sample as a waveguide… Channels in x = Channels out

How to describe this scattering? : 

How to describe this scattering? …and add disorder to mix the channels Channels in x = Channels out

Field at an outgoing channel : 

Field at an outgoing channel Outgoing channel Ingoing channels random, uncorrelated scattering coefficients =1

Controlling channels : 

Controlling channels What happens if we could control the incident channels… =1

Controlling channels : 

Controlling channels We choose the phase to maximize the amplitude of Eb =1

Controlling channels : 

Controlling channels We choose the phase to maximize the amplitude of Eb =1

Controlling channels : 

Controlling channels By controlling the incoming channels we control how light propagates! =1

Outline : 

Outline Scattering in optics Wave front shaping Focusing through opaque materials Focusing inside opaque materials

Speckles : 

Speckles sample target total field in target

Basic idea : 

Basic idea Digital feedback system sample target Divide incoming wavefront in N segments

Basic idea : 

Basic idea sample phase modulator with N segments target total field in target

Outline : 

Outline Scattering in optics Wave front shaping Focusing through opaque materials Focusing inside opaque materials

Slide 19: 

LCD Experimental setup Spatial amplitude and phase modulation using commercial TN LCDsvan Putten, Vellekoop & Mosk,Appl. Opt. 47, 2076 (2008).

Slide 20: 

LCD Sample: 10 µm layer of TiO2 pigment Light source: 633 nm HeNe laser Feedback: 1 pixel of CCD camera Experimental setup

Focusing light through paint : 

Focusing light through paint Focus is more than 1000 times brighter than the background Vellekoop & Mosk. Opt. Lett. 32, 2309 (2007)

Perfect focusing : 

Perfect focusing Vellekoop, Lagendijk & Mosk, Nat. Photon. 5, 320 (2010) Wave front shaping Diffraction limit of the sample

Slide 23: 

Teeth (ex vivo) Paint Daisy petals Scotch tape Prepared chicken Egg shell Works on a variety of materials

Outline : 

Outline Scattering in optics Wave front shaping Focusing through opaque materials Focusing inside opaque materials

Focusing inside : 

Focusing inside Open problem in science, technology and biomedical imaging Highly relevant for near-field superresolution with metamaterials. Need feedback signal from inside

Focusing inside : 

Focusing inside Use fluorescent probe particle (150 nm) forfeedback.

Enhanced fluorescence : 

Enhanced fluorescence Size of the sphere (same scale) 20x more light! Plane wave illumination Shaped wave illumination

Intensity vs. depth : 

Intensity vs. depth Conventional optics corrected for all aberrations (classical adaptive optics) Wave front shaping Vellekoop, van Putten, Lagendijk & Mosk, Opt. expr. (2008) Wave front shaping works independent of depth

Size of the focus : 

Size of the focus Resolution illumination

Size of the focus : 

Size of the focus Resolution illumination Wave front shaping

Size of the focus : 

Size of the focus Resolution illumination Wave front shaping Resolution detection van Putten, Lagendijk & Mosk, submitted

Conclusions : 

Conclusions Disorder no longer a nasty problem Light can be focused at any location in and outside a disordered material Wave front shaping is a powerful tool to control light propagation

Slide 33: 

As discussed in Nature Physics 4, 91 (2008)

Resolution and contrast : 

Resolution and contrast Normal lens: Wavefront error deteriorates focus size Opaque lens: Wavefront error scattered into background (deteriorates focus contrast)

Graphical representation : 

Graphical representation contribution of segment 1 contribution of segment 2 contribution of segment N Maximize Eb

Global maximum : 

Global maximum before after global maximum

Finding the optimal wavefront : 

Finding the optimal wavefront Adjust phase of individual segments until contribution is in phase with total field

Intensity of focus : 

Intensity of focus
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