23 June 2010

50 years on, the laser shows no sign of retiring

By Dr Manas Kumar Haldar

(Published in’Campus & Beyond’, a weekly column written by Swinburne academics in the Borneo Post newspaper)

Technologies are invented, developed and retired. For example, the venerated vacuum tube family has almost retired. Its last member, the cathode ray tube, is holding out as computer and TV displays and will be replaced soon. But the laser, which was invented on 16 May, 1960 by Theodore Maiman shows no sign of retirement. Like the hand phone, it is present almost everywhere. Check out in a supermarket and you will find a laser. Go to a lecture and you find the speaker wielding a laser pointer.

Light is all around us, so what is so special about lasers? The power in ordinary light is spread over many colours. Although a single colour can be extracted from it by various techniques, its power is small and it is difficult to manipulate. On the other hand, a laser can emit considerable power at almost a single colour. For example, a red laser emits only red light. This allows many applications.

According to physicists, a quantum of light, called a photon, is produced when an electron, the primary charge carriers in electric current, moves from a higher energy state to a lower energy state. Usually electrons occupy the lowest energy states. In a laser, electrons are “pumped” to the higher energy state by such means as flash lamps or electric currents, just like water is pumped up to a reservoir for it to flow down. As a result, there are more electrons at the higher level than in the lower level. This condition is called population inversion. Moreover, in a laser, photons move back and forth between two mirrors and can stimulate the generation of more photons. This means amplification of photons, i.e. light, and the process is called stimulated emission.

The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. The characteristic of stimulated emission is that the photons are in phase synchronism. It is something like an army marching in step. On the other hand, in spontaneous emission which produces ordinary light, photons are emitted randomly. It is like a crowd of people running helter skelter.

Although the first laser invented by Maiman was made with a ruby rod, it appears as if almost any material can be used to make a laser. We can even use air.

So why will the laser not retire soon? The supermarket check-out and the laser pointer have already been mentioned. But there are many other uses. High power lasers are used extensively in the industry for metal cutting and welding. Lasers are also used for LASIK surgery. The purpose of LASIK surgery is to reshape the cornea of the eye to correct eye defects, such as short sightedness (myopia). This is done with a laser. Want to remove your tattoo, wrinkles or pimples? You can visit a beautician well trained in using lasers for that purpose. Want some entertainment? Go to a laser light show. These can be found, for example, in many pop music concerts.

Many of us have seen tweezers, but have you heard of optical tweezers? Laser light can trap atoms and molecules. For example, microbes and even DNA molecules can be moved with optical tweezers. Do you know that Apollo astronauts put mirror arrays on the moon? The distance of the moon from the earth could be measured from the time required by a light pulse to go to the mirror and return. No wonder back on earth, lasers are widely used for surveying. Do you know that a blue-violet laser makes the Blu-ray player possible? Lasers have so many uses that it is difficult to list them all in this article, let alone describe them.

It will be wrong to think that lasers produce only visible light. Lasers have been made to produce a wide range of radiations from infrared to X-rays. No other device has been so versatile. Obviously, lasers are widely used for scientific research. But think of one way how invisible laser light has affected the lives of all of us. The infrared laser together with optical fibre has made fibre optic communication possible. Thousands of miles of fibre cables have been laid. We are waiting for the day when the fibre will reach our homes for us to enjoy “real” broadband. Technologically, this is already feasible.

Finally, where does this all fit in with Swinburne University of Technology? At the Melbourne campus, there is an entire research centre devoted to laser applications. They have made some significant advances in high density computer memories using lasers.

At the Sarawak campus, an optical laboratory is under development where a small team plans to develop other applications for lasers.

Dr Manas Kumar Haldar is Associate Professor with the School of Engineering, Computing and Science, Swinburne University of Technology Sarawak Campus. He can be contacted at mhaldar@swinburne.edu.my