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Optomechanics of Soft Materials

Ruobing Bai's picture

Optomechanics of Soft Materials


Ruobing Bai and Zhigang Suo


Some molecules change shape upon receiving photons of certain frequencies, but here we study light-induced deformation in ordinary dielectrics with no special optical effects. All dielectrics deform in response to light of all frequencies. We derive a dimensionless number to estimate when light can induce large deformation. For a structure made of soft dielectrics, with feature size comparable to the wavelength of light, the structure shapes the light, and the light deforms the structure. We study this two-way interaction between light and structure by combining the electrodynamics of light and the nonlinear mechanics of elasticity. We show that optical forces vary nonlinearly with deformation and readily cause optomechanical snap-through instability. These theoretical ideas may help to create optomechanical devices of soft materials, complex shapes, and small features.


Pradeep Sharma's picture

Ruobing, I enjoyed reading your paper...congratulations on a nice piece of work! Have you guys made any progress in developing numerical methods to solve general 3-D boundary value problems? You briefly allude to this in one of your paragraphs.

Harold S. Park's picture

I also enjoyed reading this - very nice work - and I am glad to see other mechanicians working on interesting multi-physical problems.  I have also posted a recent work we have done looking at optomechanical coupling in hard, metal nanostructures, driven by the phenomena of surface plasmon resonance.  The phenomena is not as general as your formulation, but hopefully interesting nonetheless.

Ruobing Bai's picture

Dear Harold,

Congratulations on the nice work! I just downloaded your paper. The subject of combining electromagnetism and mechanics is very interesting. I hope there will be more good works as yours on this kind of multiphysics problem.

Ruobing Bai's picture

Dear Pradeep,

Thank you for your comments! We have thought about it for a while but have not tried very deeply. We think there are two possible ways of doing this. The first way is to solve this boundary value problem in incremental steps, and each time increase small amplitudes of mechanical and optical loads, solve for the displacement and update the body. This is basically the idea of finite element. The second way is mentioned in Section 8, that the optical force can be treated as an additional boundary condition in this case. Therefore optical forces can be directly added to the boundary of the body, and numerical tools such as COMSOL will be possible to be used.

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