#total internal reflection

In nature, color comes from many sources: like the pigmentation of skin and hair, the structural iridescence of a butterfly’s wings, or the refraction of a rainbow from water droplets. Recently, scientists discovered another source of brilliant color in simple, hemispherical water droplets. 

When small droplets form on a transparent surface, they form concave shapes capable of total internal reflection. This means that two light rays entering from the same angle can follow different paths inside the droplet. After reflecting several times, the light rays exit the droplet with a phase difference and how large that phase difference is determines the color. Check out the video below for some brightly colored examples of the effect. The researchers hope the technique will eventually be suitable for creating dye-free, color-changing technologies. (Image credit: F. Frankel; video credit: MIT News; research credit: A. Goodling et al.)

Cleaning nanowires to get out more light

Some materials can efficiently convert the electrons in an electrical current into light. These so-called semiconductors are used to create light-emitting diodes or LEDs: small, light, energy-efficient, long-lasting devices that are increasingly prevalent in both lighting and display applications.

The color, or wavelength, of the emitted light can be determined by choosing the appropriate material. Gallium arsenide, for example, emits predominantly infrared light. For shorter wavelengths that move into the blue or ultraviolet region of the spectrum, scientists have turned to gallium nitride. Then, to tune down the emission wavelength, aluminum can be added, which alters the spacing between the atoms and increases the energy bandgap.

However, numerous factors prevent all the radiation created in the semiconductor escaping the device to act as an efficient light source. Firstly, most semiconducting materials have a high refractive index, which makes semiconductor-air interfaces highly reflected--at some angles all light bounces backwards in a process known as total internal reflectivity. A second limitation is that imperfections at the surface act as traps that reabsorb the light before it can escape.

The unstable boundary produces a kaleidoscope effect, showing the viewer endless reflections of the universe further and further back in time.

Introduction Reflection is a fundamental concept in physics that describes how waves, such as light or sound, bounce off a surface. When these waves encounter a surface, they are reflected back into their original medium rather than being absorbed or transmitted. Law of Reflection The behavior of a wave upon reflection is governed by the law of reflection, which states: The incident ray, the…

Introduction Fiber optics refers to the technology of transmitting information as pulses of light through strands of fiber made from glass or plastic. It’s a key technology in telecommunications, enabling long-distance and high-speed data transmission. Basic Principles The fundamental principle behind fiber optics is total internal reflection. When light traveling through a medium hits a…