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SUMMARY:Biogenic light induced tuneable photonic crystals - Dvir Gur - Wei
 zmann Institute of Science\, Rehovot
DTSTART:20160519T130000Z
DTEND:20160519T140000Z
UID:TALK66200@talks.cam.ac.uk
CONTACT:Sharon Connor
DESCRIPTION:Strikingly brilliant structural colours using 2D or 3D arrays 
 of chitin or cellulose fibers\, calcite or guanine crystals were independe
 ntly evolved by organisms to fulfil a variety of functions. Many of these 
 optical systems are based on intra-cellular arrays of thin guanine crystal
  platelets. \n\nThe silver iridescence of fish scales and skin\, as well a
 s the brilliant blue colour of the neon tetra lateral stripe\, are both pr
 oduced by constructive interference of light reflected from ordered arrays
  of guanine crystals separated one from the other by cytoplasm [1]\, [2]. 
 \n\nCertain families of marine crustacean copepods produce some of the mos
 t spectacular colours in nature. They produce different colours covering t
 he whole visible spectrum\, and each colour is characterized by well-defin
 ed spectral characteristics. By combining correlative reflectance and cryo
 -electron microscopy image analyses\, together with optical time lapse rec
 ording and reflectance modelling\, we first showed that each colour is cre
 ated by specific and precise cytoplasm spacings within stacks of uniformly
  thick guanine crystals [3]. In addition\, the same organisms have the rem
 arkable ability to change their reflectance spectrum in response to change
 s in the light conditions. This change is reversible\, and is both intensi
 ty and wavelength dependent\, forming truly tuneable photonic crystal arra
 ys [4]. \n\nThe insights gained from the understanding of how biology modu
 lates reflectivity can provide inspiration for the design of artificial op
 tical systems with properties yet hardly achievable\, if at all\, in artif
 icial materials.\n
LOCATION:Unilever Lecture Theatre\,  Department of Chemistry
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