Light in general and lasers in particular are ruling the world of science and technology for decades now. Interdisciplinary applications of lasers are in the fields of medical science, communication, defence, security, data storage and more.
The most important application of light as a laser is in day-to-day challenges faced by people of the world, due to its unique characteristics. This article focuses on laser and its major applications.
What laser is?
The word laser stands for light amplification by stimulated emission of radiation. The unique property of laser, emission of coherent light, makes the applications of laser cutting and lithography possible. Laser pointing is also an application based on the property of the laser to follow a narrow path over great distances.
In the vast heaps of applications, laser finds a place in optical disk drives, laser printers, optical fibres (hence, optical communication), barcode readers, laser surgery, dermatology, cutting, welding, photo rejuvenation, endarterectomy, ophthalmology, military law enforcement devices for locating targets and measuring range and speed, and laser lighting displays in entertainment, among others.
Having properties like coherence and mono-chromaticity, a laser can be focused as a narrow beam over a very small area up to distant places without any reduction in power. Hence, a laser produced by stimulated emission of light can be employed in applications where light, if required, cannot produce spatial coherence using simpler technologies.
During 1960s, when the laser was invented, it was known as the solution looking for a problem, as a laser finds its utility in varied applications.
Applications of lasers
The various applications of lasers are described below.
The purpose of knocking down an enemy tank requires that the range (locating the target) is accurate. High intensity and low divergence of the laser satisfies this need. Neodymium and carbon-dioxide lasers are used as standard items for artillery and tanks. Laser rangefinders are lightweight, having reliability and superior range accuracy.
When a laser beam is directed towards a target and reflected light from the target is received by an optical system and detected, corresponding time taken is measured. Half the time recorded is multiplied by the velocity of light and product to calculate range.
A laser finder is powerful than a microwave radar as the former provides better collimation, which makes high angular resolution possible. Having the advantage of greater radiant brightness and the fact that it is directional even after travelling long distances, the size of emitting system is gradually reduced. A laser rangefinder of medium range (up to 10km) is used in several defence areas, including:
1. Tank laser rangefinders for battle tanks
2. Portable laser rangefinders used in field artillery fire-control systems
3. Air-borne laser rangefinders for air forces
4. Laser walkie-talkie rangefinders
Another application of laser is lidars (or, laser radars). These are better than microwaves, as lasers can be focused with lenses and mirrors easily while microwaves need huge antennae and components. Moreover, dimension and distance of target can be obtained with high accuracy in case of lidars.
The types of lasers used are carbon-dioxide lasers, Q-switched or gallium-arsenide semiconductor. High power output with requisite spectral purity production capacity of CO2 laser is better for this purpose. High frequency of CO2 lasers also produces high Doppler shift even from slow-moving targets. Fine beam width and high Doppler shift give CO2 lasers an unparallelled imaging capability. Radar systems are used for measuring radial velocities to track low-flying aircraft and slow-moving objects.
Then, there are laser-guided anti-missile systems that can be guided by an infrared beam emitted from a laser, with extremely small divergence that can be achieved in the following four ways:
1. The laser beam is used to illuminate the target tank. The anti-missile system then homes in on the target, as the latter becomes a source of back-scattered radiation.
2. A laser beam is used to provide guidance instructions to the missile.
3. The missile itself carries a laser scanner and a seeker for active homing on target.
4. The missile rides the laser beam towards the target.
In an anti-missile defence setup, a laser is used to dispose of the energy of the warhead, by partially damaging the missile. Tremendous energy is required to completely destroy the missile. According to predictions, lasers will ultimately make inter-continental ballistic missiles obsolete.
There are many limitations, however, to the laser playing an anti-missile role. Huge power stations are required to produce huge power lasers. CO2 and chemical lasers developed in the USA and Russia produce huge power in continuous mode, which is sufficient to destroy enemy battle tank.
Optical techniques play a major role in storage of high-density data. These are based on the principle that, when a powerful laser illuminates a thin layer of metal, its optical properties change. As a laser beam can be focused on points smaller than one micro diameter, it takes less than one square micro to record one bit of data, that is, 100 million per square cm. There are laser CDs and DVDs available in the market with the required data stored in the form of audio, video, document, etc. Interestingly, erasable disks are now coming into the picture, something that was considered to be a drawback.