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Our Plans. Invisibility: Is this possible? Yes!!! How it works & when we can buy our invisibility clothes? Energy from light: Solar cells & solar cell paints; Lasers: What they are & how they work; Laser tweezers: moving things with light without touching; - PowerPoint PPT PresentationTRANSCRIPT
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1. Today : Review of Science & technology of Light
2. Class #23
1. Invisibility:• Is this possible? Yes!!!• How it works & when we can buy
our invisibility clothes?
2. Energy from light:• Solar cells & solar cell paints;
3. Lasers:• What they are & how they work;• Laser tweezers: moving things with
light without touching;• Laser applications: science,
technology, & everyday life;
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http://www.youtube.com/watch?v=JKPVQal851U
Is this possible???
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Invisibility cloaks made of metamaterials
http://www.youtube.com/watch?v=Ja_fuZyHDuk http://www.telegraph.co.uk/scienceandtechnology/science/sciencenews/3353461/Harry-Potter-invisibility-cloak-a-step-closer-to-reality.html
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How the cloaks of invisibility work:
No rays reflected from the cloak-surrounded object - it can not be seen
& is invisible
First cloak of invisibility demonstrated to work at a
particular wavelength of light
Recall that we did not see the glass rod immersed in vegetable oil because there was no light coming from the glass-oil interface
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n<0
n>0air
Negative refraction
Unusual bending of rays of light
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Where would we see the fish if water had negative refraction index
Note that the Snell’s law of refraction still works at such interfaces
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Structured metamaterials that can achieve negative refraction
Model Image of a nano-fabricated material
The size of these features has to be much smaller than the wavelength of light
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Transforming solar energy to electricity
Solar Cells
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solar cells for energy by converting sunlight directly into electricity.
The sun radiates ~1000W per square meter (see the map), so a 10 x 10 cm solar cell is exposed to nearly 10 watts of radiated power. Depending on the quality of the cell, it can produce an electrical output of 1 - 1.5 watts.
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Light shining from this side:
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Sunlight striking the photovoltaic cell is absorbed by the cell.
The energy of the absorbed light generates particles with positive or negative charge
Therefore, when an external load, such as an electric bulb or an electric motor, is connected between the front and back electrodes, electricity flows in the cell.
Principal scheme of a solar cell
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Flashlight
Lightbulb
Laser
Lightbulb
Flashlight
Laser
Rays: Waves:
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Principal components & how lasers work
1. Gain medium2. Laser pumping energy3. Mirror (100% reflection)
4. Output coupler mirror (98-99% reflection);5. Laser beam
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• The term “LASER" is an acronym for Light Amplification by Stimulated Emission of Radiation.
• Laser light is emitted in a narrow, low-divergence beam
• Lasers are emitting light with a narrow monochromatic wavelength spectrum.
Laser in a research lab:
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Intensity-distribution curve of light from a White fluorescent tube
Intensity-distribution curve of light from a incandescent lamp
Compare different light sources:
Laser
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Some of numerous applications• In CD, Blue-Ray, DVD, andHD-DVD players,• Bar code readers;• Laser pointers & laser tweezers;• welding metal and other materials;• "marking"—producing visible patterns such as letters;• Military applications: range-finding, target designation, and
illumination, weapons;• Medicine: laser surgery (i,.e., correction of cornea in the eye),
diagnostics, and therapeutic applications; • Holography;• Laser microscopy;
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Moving Matter with Light without touching ???
To explain why tails of comets always point away from the Sun, Kepler suggested that the Sun was exerting a sort of radiant pressure. This led him in 1609 to propose sailing from the Earth to the Moon on light itself. This was and still is the stuff of science fiction.
Johannes Kepler
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Moving and shaping matter with light400 years later Kepler's ideas about moving matter with light are a reality(manipulated with invisible infrared light)
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A highly simplified view on How “Optical Trapping” WorksAlong beam axis:Laser beam
Refraction changes light (photons) propagation direction; In return, the particle experiences an opposite force; Need refractive index of object > than that of medium;
In the lateral plane:
cPowerF ~ rlaser powefor mW of pN pNFgravity
310~
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Equivalent ways of steering
Objective
Focal Plane
Prism
Objective
Multiple traps: beam steering and shaping using spatial light modulators
Objective lens
Focal planePhase-only SLM
Image
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Manipulation of multiple micron-sized objects
Manipulation by CW Nd: YAG (λ=1064nm), visualized by HeNe laser (λ=632.8nm)
9x9 arrayBacteria Pseudomonas aeruginosa:
Manipulating bacteria
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