Strong optomechanical interaction is achieved in novel bi-layer photonic crystals
Bi-layer systems have been studied in various fields in physics, such as quantum Hall
systems, quantum wells, graphenes, superconductors, and strongly-correlated electron
systems. Here, the authors realized a novel bi-layer photonic crystal * system (schematically
shown in the figure), for the first time, which can retain most of high performance in conventional
single-layer photonic crystal slabs but of which new degree of freedom in the
vertical direction leads to enormously large optomechanical interaction. Usually, optical
force (that is , radiation force) is very weak because a photon has very small momentum,
but it can be greatly enhanced by this structure. The authors experimentally demonstrated
large displacement of the slab by optical pumping via optically-generatged force. The energy
conversion efficiency is as large as 0.4microN/pJ, which is much larger than conventional
optical tweezers. This bi-layer configuration of photonic crystals may have strong impact
on emerging optomechanics engineering, and has potential to be applied to ultra-energy-
efficient optical force generators.
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LJ12295
How the motion of micro-organisms can change the viscosity of liquids?
Take a droplet of liquid and estimate its viscosity by shearing it
between your fingers. This is the common perception of viscosity. If
some particles (like pollens for example) are present in the droplet, we
call it a suspension. The viscosity of a suspension increases in a
non-linear way with the number of particles. Now, instead of pollen
seeds, imagine that the particles are micro-organisms such as
spermatozoa, micro-algae or bacteria which can swim in fluids and are
classified as micro-swimmers or motile cells. In this letter, we show
that a given number of motile micro algae (Chlamydomonas Reinhardtii)
suspended in a droplet of water drastically changes the viscosity of the
resulting suspension (when compared to the same suspension made out of
dead cells). It is therefore possible to quantify the averaged motility
of a large population of a billion of cells. We believe that this study
will pave the way towards reliable quantitative study on other
suspension of swimming cells such as spermatozoa for example, for which
motility has a direct impact on fertility.
