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Light-Matter Interaction: Engineering Light Behaviour at Nanoscale

Submitted By: 

Vishal Duggal
Light, as we know, sustains the web of life on the Earth. Sunlight (absorbed by chlorophyll) is very essential for photosynthesis that takes place in plants for making the food we eat and releasing the oxygen that we breathe. Besides this, many organisms make use of this interaction in basic sensory mechanisms for guiding their behaviour either through a complex process like vision or relatively simpler photosens¬itivity of micro-organism. From engineering standpoint, it is this very interaction between light and matter that forms the basis of a wide range of technologies including lasers, LEDs and atomic clocks. 
 

 
Fig.1: Rainbow - Light of varying colours has different refractive indices
 
It is well-known that matter is composed of atoms. These atoms are comprised of a nucleus that is surrounded by electron energy shells. Light interacts with these electron shells. Light as energy can be absorbed by an electron shell and then various actions can take place. When light interacts with matter it can do several things depending on its wavelength and what kind of matter it encounters: it can be transmitted, reflected, refracted, diffracted, adsorbed or scattered.
 
Light interacts either like a particle or a wave that behaves as a particle that undergoes absorption, scattering or pair production depending on atomic number and frequency of light. When the wavelength of light is comparable to inter atomic distance, it behaves like a wave and gets diffracted. For very high intensity light the interaction becomes non-linear and is dominated by frequency mixing processes.
 
Multidisciplinary Applications
 
In fact, the study of light is a multidisciplinary science involving many branches like medicine, architecture and entertainment. Light has profound implications for the field of medicine both as a cause of disease as UV damage of DNA and as a therapeutic agent as photodynamic therapy. Such processes are the basis of science of photobiology which could be defined as the study of the effects of visible and ultraviolet light from natural sun light as well as artificial sources on living matter. 
 
Besides being striking examples of architecture, some buildings demonstrate the powerful effect through elements like space, light, geometry and materials that can have change   on our mood. With abundant views and natural light, people can observe the activity and the natural world outside and those outside have a glimpse of what is happening inside. They are separated yet connected and help to connect their communities together.
 
Lasers have also proved their usefulness in the realm of art and entertainment from "light shows" to compact discs (CDs) and digital video discs (DVDs), to special effects in the movies. 
 
Applications in Medicine
 
Many forms of light (electromagnetic radiation) find some application in medicine. Breakthroughs in light technology have revolutionized the medical industry. The process of medical imaging involves creating visual representations of the interior of a body for further medical analysis. 
Medical imaging, surgical procedures as well as diagnosis rely upon the use of light. Such imaging is generally used in medical fields such as neuroscience, cardiology, psychiatry, and psychology, amongst others. Visible light is the most common and important as it is used to see and evaluate patients via clinician’s eyes. Nowadays, visible light is used for medical photography.
 
 
Fig. 2: X-ray -  Optimising  eectromagnetic radiant energy
 
The role of light in medical procedures has grown immensely. Lasers of many different colours are used in all sorts of diagnostic and surgical procedures. Lasers come in a variety of wavelengths and may be used to break kidney stones, cauterize bleeding or vaporize tumours. Argon laser has been used to stop liver bleeding. Infrared light is used for imaging and also for warming premature infants. Radio waves are used in MRI imaging. Ultraviolet light can be used for sterilization. X-rays are used to see bones and kill tumours. Ultraviolet light is used psoriasis whereas ultraviolet lasers are used in corneal refractive procedures.
 
Higher energy electromagnetic energy (X-rays) are used in CT machines and for plain film X-Ray imaging. X-rays can treat certain forms of cancer. Gamma rays as higher energy forms of electromagnetic radiation can be used for cancer treatment. Gamma rays are also detected in PET scans and used in gamma knife surgery for brain tumours.
 
Applications in Architecture
 
Lighting is considered as a very important field in architecture, interior design and electrical engineering that is concerned with the design of lighting systems such as natural light, electric light or both to serve human needs. The design process takes into account the amount of light required. Accompanied by the belief that light and brilliance could help in creating iconic architecture and a better human world, glass and metal have been innovatively transformed to create crystalline images. As a result, it has been shifted from an internal space-form to the external surface in architecture. 
 
Fig. 3: Nanotechnology - Nanocrystals emiting visible light
 
There are examples in contemporary architecture that have used light in a masterly way through the control of light and materials as they get each space to show the user its own personality calmly. In some buildings light becomes almost unreal by combining it with the darkness of materials, stone, reflections on the water and steam which builds a unique atmosphere.
 
Sometimes, photometric studies are referred as "layouts" or "point by points." These are used to simulate lighting designs for projects before they are built or renovated. Such types of approaches help the architects, lighting designers and engineers to determine whether a proposed lighting setup will deliver the amount of light intended. They also determine the contrast ratio between light. Such studies are referenced against IESNA or CIBSE recommended lighting practices for the type of application.
 
Design aspects should take into account safety or practicality in the course of maintaining uniform light levels, avoiding glare or emphasising certain areas. A specialized lighting design application is used to create and combine the use of two-dimensional digital CAD drawings and lighting simulation software. Accompanied by the belief that light and brilliance could help in creating iconic architecture and a better human world, glass and metal have been innovatively transformed to create crystalline images. Some projects are remarkable not only for innovative way of handling tangible materials but also for imagination regarding the medium of light. Theories of fragmentation and fluidity are now well-known design techniques in architectural field.
 
Applications in Entertainment
 
It is proved that professional illumination provides much more than just the right level of brightness. It creates the mood and supports the compositions and concepts of the lighting designers. Creating various moods that speak for emotions is one of the main functions of lighting and makes it a central design element in film and TV productions. Right type of light denotes tension, excitement, drama, joy and fascination. Thus lighting plays an important role in creating unforgettable moments in TV and movie productions.
 
 
Fig. 4: Laser projector - Revolutionising  home entertainment
 
Lasers have also proved their usefulness in the realm of art and entertainment. A laser beam is a wand of light that can be beautiful as well as practical. The sight of a deep red sunset or multicolour rainbow often inspires feelings of happiness, romance, and even awe. Since many centuries artists have tried to reproduce light's beauty in paintings. Inventors have given artists mechanical tools such as the camera that uses light to create art. This is really entertaining as well as beautiful as seen in the motion picture.  Young Sherlock Holmes was the first movie to use a laser to print images directly onto the film. It was released in 1985 and ILM (Industrial Light and Magic) created the most special effects. In one of its scene, a painted knight on a stained glass church window comes to life. Then Knight jumps down from the window and chases a priest out of church. Similarly, many science fiction movies not only utilize lasers in creating their special effects but also regularly depict lasers or laser like devices. In fact, real lasers have added a fresh, visually exciting dimension to the world of entertainment. It is hoped that scientists and artists will continue to blend their talents to produce many inventive and dramatic new forms of laser-based entertainment in future. 
 
Can light-matter interaction be enhanced?
 
Most light-matter interaction processes are forbidden by electronic selection rules limiting the number of transitions between energy levels. As atom is much smaller than the wavelength of the light that gets emitted—about 1/1,000 to 1/10,000 as big— it substantially impairs the interactions between the two. However, a new Massachusetts Institute of Technology (MIT) study could open up new areas of technology to get the momentum of light particles, called photons, to more closely match that of electrons, which is normally many orders of magnitude greater.
 
Fig. 5: Solar technology -  Aiming at higher efficiency
 
According to researchers, if we can "shrink" the wavelengths of light by orders of magnitude, bringing it down almost to the atomic scale, it enables a whole range of interactions that relate to absorbing or emitting light. In the two-dimensional material called graphene, light can interact with matter in the form of plasmons, a type of electromagnetic oscillation in the material that makes interactions at a much higher magnitude than they would be in ordinary materials. Utilising these forbidden transitions could open up the ability to tailor the optical properties of materials in unprecedented ways.
 
This research systematically explores how 2-D materials improve light-matter interactions, laying a theoretical foundation for faster electronic transitions, enhanced sensing, and better emission, including the compact generation of broadband and quantum light. Narrowly confined, the light can then be absorbed by the semiconductor, or emitted by it. This shrinkage could lead to new kinds of solar cells capable of absorbing a wider range of light wavelengths, which would make the devices more efficient at converting sunlight to electricity. It could also lead to production of devices such as lasers and LEDs that could be tuned electronically to produce a wide range of colours. 
 
Summing up
 
Enhanced interaction of light with matter is all set to revolutionise the fields of medicine, architecture, entertainment industry and many more. In fact, using more advanced technology has infinite possibilities for a variety of applications across multiple disciplines such as spectroscopy and sensing devices, ultrathin solar cells, new kinds of materials to absorb solar energy, more efficient highly tunable lasers or light-emitting diodes (LEDs), and photon sources for possible quantum computing devices.