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;

Is this possible???

Invisibility cloaks made of metamaterials

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

n<0 n>0 air Negative refraction Unusual bending of rays of light

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

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

Transforming solar energy to electricity Solar Cells

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 watts.

Light shining from this side:

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

Flashlight Light bulb Laser Light bulb Flashlight Laser Rays: Waves:

Principal components & how lasers work 1. Gain medium 2. Laser pumping energy 3. Mirror (100% reflection) 4. Output coupler mirror (98-99% reflection); 5. Laser beam

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:

Intensity-distribution curve of light from a White fluorescent tube Intensity-distribution curve of light from a i ncandescent lamp Compare different light sources: Laser

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;

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

Moving and shaping matter with light 400 years later Kepler's ideas about moving matter with light are a reality (manipulated with invisible infrared light)

22 A highly simplified view on How “Optical Trapping” Works Along 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:

Equivalent ways of steering Objective Focal Plane Prism Objective Multiple traps: beam steering and shaping using spatial light modulators Objective lens Focal plane Phase-only SLM Image

24 Manipulation of multiple micron-sized objects Manipulation by CW Nd: YAG (λ=1064nm), visualized by HeNe laser (λ=632.8nm) 9x9 array Bacteria Pseudomonas aeruginosa: Manipulating bacteria

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