The many wonders of light
C Sivaram Dec 15, 2015
The year 2015 was declared the International Year of Light and Light-based Technologies by the United Nations to raise awareness about how optical technologies promote sustainable development and provide solutions to worldwide challenges in varied areas of life. At this point, one could recall the 2014 Nobel Prize for Physics which was jointly awarded to three physicists — Hiroshi Amano, Isamu Akasaki and Shuji Nakamura. They essentially developed the blue light emitting diode (LED) which allows the production of white lamp sources which have a very high energy efficiency ( i.e. high conversion efficiency of electric current energy to light) and long lifetimes than incandescent bulbs.
In fact, this month in Karnataka, LEDs have been distributed on a mass scale (at lower prices) to enable people to use it for domestic lighting to substantially save power. As about one-fifth of the world’s power is used for lighting, this use of optimally-efficient LEDs would reduce the percentage of total power consumed to less than four per cent. Of course, sunlight has been illuminating the earth for five billion years. All our food is produced by photosynthesis, a complex chemical process by which green plants synthesise organic compounds in the presence of sunlight, chlorophyll being the main catalyst. The mechanisms underlying photosynthesis when unravelled in greater detail is expected to help in more efficient use of solar energy. As sunlight hardly penetrates more than several metres, many of the benthic life at ocean depths have their own source of bioluminescence. Coal, the main fossil fuel we use is just ‘buried sunlight’.
Prism of colours
As is well known, Isaac Newton first demonstrated that white light can be broken into colours and then studied the spectrum. He proposed the corpuscular theory of light, that it propagates as a stream of particles. Thomas Young showed wave theory was essential in understanding phenomena like interference and diffraction. Light as wave motion was well accepted in the 19th century and was bolstered by Maxwell’s electromagnetic theory giving wave equations for the propagation of varying electromagnetic fields.
Maxwell and others thought that the waves needed a special medium to propagate in space — the so called ether. Michelson-Morley experiment tried to detect velocity differences of light beams propagating parallel and perpendicular to earth’s motion through ether and found a null result. This led to Einstein’s special theory of relativity.
The constancy of light speed in vacuum led to the phenomena of time dilation and length contraction for relativistic particles. Later, the observation of the bending of light by the sun’s gravitational field during a total solar eclipse established the general theory of relativity. Length and time standards are based on atomic clocks, involving electronic energy levels. These clocks now lose a second in a billion years.
In 1905, Einstein showed that the photoelectric effect could only be explained on the assumption that light consists of a stream of discrete photons with energy proportional to the frequency. The photoelectric effect paved the way for myriad applications ranging from automatic opening of doors to sophisticated photo-detectors and photovoltaic cells to produce power. Also, optical fibres have considerably increased the channel carrying capacity of telecommunications. Light can be confined in the core of optical fibre, over many kilometres by total internal reflections. There is enough optical fibre currently to encircle the earth more than 25,000 times. This enables text, speech and film to be scurried across the internet.
Light-led technology
In 2009, Charles Kao was awarded one half of the Nobel Prize for Physics, while the other half was shared by Willard Boyle and George Smith for inventing the so-called ‘charged coupled device’, better known as CCD. While Charles Kao’s work revolutionised communication of all information by light, CCD, consisting of millions of light sensitive cells arranged in myriad rows and columns revolutionised photography. Crystal clear pictures of celestial objects, medical imaging and numerous commercial and industrial application are due to CCDs (Hundred years earlier, in 1909, Gabriel Lippmann got the Nobel Prize for the technique of colour photography).
Just a hundred years ago, Einstein gave the concept of stimulated emission, which suggested amplification of light. That light exerts pressure was discovered by physicist Pyotr Lebedev. Today, laser beams of high intensity can produce pressures of millions of atmospheres and can heat and confine plasma to hundred million degrees and more. Ironically, lasers can also cool matter through laser cooling.
Lasers are of ubiquitous use in surgery — cutting materials and manipulating materials (including DNA) by light pressure in so called tweezers. Physicists have also slowed down light in atomic vapours. Also optomechanical crystals have been used for optical quantum information processing and storage. Holographic data storage that can store entire libraries in a single crystal and ultrafast computing at the speed of light are already in place. Twenty years ago, photonic crystals were introduced, where photons travel like electrons in a crystalline solid. Atomic spectroscopy has enabled us to detect rare elements like platinum or thorium in distant stars by their characteristic spectral signature, while the Doppler effect has enabled us to map their motions. Raman spectroscopy is used to detect traces of pollutants.
Photonics applied to medicine
Within a decade or less, laser may emit beams with spot sizes of a nanometre, about that of a molecule, and microscopes using laser sources with apertures the size of a single molecule can result in fast direct sequencing of DNA, RNA and other molecules. Laser Doppler flowmeters are instruments for measuring blood flow through tissues with a laser beam.
It can complement ultrasound techniques to detect blockages in arteries, kidneys, etc by observing changes in frequency of the monochromatic light beam. Laser endoscope can peer inside organs, i.e. a non-invasive diagnosis. Laser beams are used now to unblock coronary arteries narrowed by atheroma and even to remove certain types of birthmarks.
In ophthalmology, different types of lasers are used for operations on the cornea (e.g. excimer laser, to remove thin sheets of tissue) to alter curvature of corneal surface or to remove diseased tissue. The photocoagulation of retina is done with diode laser. LASIK (laser-assisted in situ keratomileusis) is, of course, a well known procedure to use laser light beam to correct both short sight (myopia) and long sight (hypermetropia).
Also surgical techniques like laser laparoscopy are now routine. Laser surgery is applied to palate to treat obstructive sleep apnoea. Laser is even used to treat varicose veins. Apart from well known CAT ( computerized axial tomography) scans, we also have Optical Coherence Tomography (OCT) to get diagnostic non-invasive three dimensional images from optical scattering of the beam from tissues.Optical fibres are also routinely used in medicine to examine internal cavities (stomach, bladders etc.). CCD’s have revolutionised medical imagining and diagnosis.
In fact, this month in Karnataka, LEDs have been distributed on a mass scale (at lower prices) to enable people to use it for domestic lighting to substantially save power. As about one-fifth of the world’s power is used for lighting, this use of optimally-efficient LEDs would reduce the percentage of total power consumed to less than four per cent. Of course, sunlight has been illuminating the earth for five billion years. All our food is produced by photosynthesis, a complex chemical process by which green plants synthesise organic compounds in the presence of sunlight, chlorophyll being the main catalyst. The mechanisms underlying photosynthesis when unravelled in greater detail is expected to help in more efficient use of solar energy. As sunlight hardly penetrates more than several metres, many of the benthic life at ocean depths have their own source of bioluminescence. Coal, the main fossil fuel we use is just ‘buried sunlight’.
Prism of colours
As is well known, Isaac Newton first demonstrated that white light can be broken into colours and then studied the spectrum. He proposed the corpuscular theory of light, that it propagates as a stream of particles. Thomas Young showed wave theory was essential in understanding phenomena like interference and diffraction. Light as wave motion was well accepted in the 19th century and was bolstered by Maxwell’s electromagnetic theory giving wave equations for the propagation of varying electromagnetic fields.
Maxwell and others thought that the waves needed a special medium to propagate in space — the so called ether. Michelson-Morley experiment tried to detect velocity differences of light beams propagating parallel and perpendicular to earth’s motion through ether and found a null result. This led to Einstein’s special theory of relativity.
The constancy of light speed in vacuum led to the phenomena of time dilation and length contraction for relativistic particles. Later, the observation of the bending of light by the sun’s gravitational field during a total solar eclipse established the general theory of relativity. Length and time standards are based on atomic clocks, involving electronic energy levels. These clocks now lose a second in a billion years.
In 1905, Einstein showed that the photoelectric effect could only be explained on the assumption that light consists of a stream of discrete photons with energy proportional to the frequency. The photoelectric effect paved the way for myriad applications ranging from automatic opening of doors to sophisticated photo-detectors and photovoltaic cells to produce power. Also, optical fibres have considerably increased the channel carrying capacity of telecommunications. Light can be confined in the core of optical fibre, over many kilometres by total internal reflections. There is enough optical fibre currently to encircle the earth more than 25,000 times. This enables text, speech and film to be scurried across the internet.
Light-led technology
In 2009, Charles Kao was awarded one half of the Nobel Prize for Physics, while the other half was shared by Willard Boyle and George Smith for inventing the so-called ‘charged coupled device’, better known as CCD. While Charles Kao’s work revolutionised communication of all information by light, CCD, consisting of millions of light sensitive cells arranged in myriad rows and columns revolutionised photography. Crystal clear pictures of celestial objects, medical imaging and numerous commercial and industrial application are due to CCDs (Hundred years earlier, in 1909, Gabriel Lippmann got the Nobel Prize for the technique of colour photography).
Just a hundred years ago, Einstein gave the concept of stimulated emission, which suggested amplification of light. That light exerts pressure was discovered by physicist Pyotr Lebedev. Today, laser beams of high intensity can produce pressures of millions of atmospheres and can heat and confine plasma to hundred million degrees and more. Ironically, lasers can also cool matter through laser cooling.
Lasers are of ubiquitous use in surgery — cutting materials and manipulating materials (including DNA) by light pressure in so called tweezers. Physicists have also slowed down light in atomic vapours. Also optomechanical crystals have been used for optical quantum information processing and storage. Holographic data storage that can store entire libraries in a single crystal and ultrafast computing at the speed of light are already in place. Twenty years ago, photonic crystals were introduced, where photons travel like electrons in a crystalline solid. Atomic spectroscopy has enabled us to detect rare elements like platinum or thorium in distant stars by their characteristic spectral signature, while the Doppler effect has enabled us to map their motions. Raman spectroscopy is used to detect traces of pollutants.
Photonics applied to medicine
Within a decade or less, laser may emit beams with spot sizes of a nanometre, about that of a molecule, and microscopes using laser sources with apertures the size of a single molecule can result in fast direct sequencing of DNA, RNA and other molecules. Laser Doppler flowmeters are instruments for measuring blood flow through tissues with a laser beam.
It can complement ultrasound techniques to detect blockages in arteries, kidneys, etc by observing changes in frequency of the monochromatic light beam. Laser endoscope can peer inside organs, i.e. a non-invasive diagnosis. Laser beams are used now to unblock coronary arteries narrowed by atheroma and even to remove certain types of birthmarks.
In ophthalmology, different types of lasers are used for operations on the cornea (e.g. excimer laser, to remove thin sheets of tissue) to alter curvature of corneal surface or to remove diseased tissue. The photocoagulation of retina is done with diode laser. LASIK (laser-assisted in situ keratomileusis) is, of course, a well known procedure to use laser light beam to correct both short sight (myopia) and long sight (hypermetropia).
Also surgical techniques like laser laparoscopy are now routine. Laser surgery is applied to palate to treat obstructive sleep apnoea. Laser is even used to treat varicose veins. Apart from well known CAT ( computerized axial tomography) scans, we also have Optical Coherence Tomography (OCT) to get diagnostic non-invasive three dimensional images from optical scattering of the beam from tissues.Optical fibres are also routinely used in medicine to examine internal cavities (stomach, bladders etc.). CCD’s have revolutionised medical imagining and diagnosis.
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