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Biophotonics www.postech.edu/~hjcha/jelyfish.jpg Electromagnetism • Its all described by Maxwell’s equations (a Scott, 1831-1879) (you need to know maths to do physics …) Total internal Reflection Total internal Reflection • Snells law of refraction (contained in Maxwell’s Equations) na sin( a ) nb sin( b ) na 1.5 a a medium a: na nb 1.2 medium b: nb nb 2 b nb 1.3 nb 2 nb 1 Demonstration Prism Use in technology • Optical fibres – all high speed telecommunication Demonstration water jet • Light concentrators for solar cells Demonstration fluorescent tube • Back-illumination for LCD TVs ~ - lightguides Demonstration glass plate & paint Use in sensing • There is an evanescent wave close to the surface, which can be used for sensing of material close (<100nm) to the surface 100nm Whispering Gallery at St Pauls Whispering Gallery mode sensors Use total internal reflection and circular orbits nsphere>nmedium Constructive interference condition gives discrete set of optical modes: resonances Resonance shift used for sensing reflection Light orbit in microsphere by quasi-total internal reflection. Demonstration WGM, Resonance frequency Use of Optical Biosensors Sensitive detection of viruses,chemicals,bacteria, proteins etc. • Healthcare (Drug Development, Diagnosis) • Defense (Detection of Explosives, chemical and biological weapons) • Police (Forensics) • Research (Protein interactions – the machinery of life) Fluorescent Proteins • Genetic code (DNA) describes fluorescent proteins • Green Fluorescent Protein (GFP) extracted from Jellyfish, and incorporated into other organisms by “genetic engineering” • A virus can add a code segment to your DNA GFP DNA 4 nanometer 10000 atoms 1/10000 of a hair GFP Variants • Genetic code engineered for different colour Bacteria expressing different FPs http://www.conncoll.edu/ccacad/zimmer/GFP-ww/tsien.html Painting the Brain – The5mm Brainbow NMR Tomography 200mm 5cm confocal two-photon microscopy photography Better transmission in the red (longer wavelength Two-Photon Microscopy • Uses two photons, i.e. a light overtone. Needs high intensities • excites only in the focus • less scattering due to doubled wavelength a neuron in the brain imaged with two-photon flourescence Femtosecond Laser sources 1 fs = 10-15 s 100fs pulses are only 30mm thick (This is the distance light is travelling in 100fs) 10ns Power concentration Pav = 1mW (like a laser pointer) Ppeak = 1mW × 10ns/100fs = 1mW × 105 = 100W! t A two-photon microscope femtosecond laser How to see cell composition without paint • Listen to the molecular vibration ! Complex molecule Water (H2O) Sound slow-motion 118 THz 1 Billion to one (1 second vibrations in 30 years audio) 95 THz Methane (CH4) 115 THz 92 THz 49 THz 47 THz 41 THz Drive the vibration with light • Green light has a frequency of 600THz, 10 times higher than molecular vibrations • Use interference of two light waves to drive vibration by the difference in frequency field amplitude 990Hz 1000Hz time 990+1000Hz (10Hz difference) 999+1000Hz (1 Hz difference) Finally: CARS Microscopy on Cells HepG2 (Human liver) living cells in a soft-agar 3D matrix Fat distribution in small droplets Human Hair on this scale Photography Scanning Electron Microscopy 50mmx50mmx20mm CARS on uni-lamellar vesicle (small soap bubble in water) Any Questions ?