What is LASER?

What is LASER?

Think of a laser and you may imagine science fiction or an exciting laser light show at a concert.

In fact lasers serve an increasingly wide range of industries and applications, and have been around for longer than you think.

The word ‘laser’ has become such a part of everyday vocabulary that many of us forget – if we ever knew this in the first place! – that it is actually formed from an acronym: Light Amplification by Stimulated Emission of Radiation. The theory of lasers was suggested in 1957 and the first laser was built in 1960 by Theodore Harold Maiman. Even 100 years ago, Albert Einstein theorised about the possibility of stimulated emission of light, although he didn’t realise its potential at the time.

Lasers probably have one of the widest range of applications of any type of device, including transmitting information via optical networks, data reading, holography, surgery, cutting metal, light displays, and coding and marking products on the production line.

Laser marking systems first came onto the market around 50 years ago. These early systems were highly scientific and not designed for harsh production environments, nor for 24/7 running – something we now take for granted. Today, laser coders have evolved to become smaller, more efficient and cost effective, and are an effective solution for coding and marking requirements in an increasingly wide range of applications.

How a laser works

All lasers share the same basic principles but are differentiated by the way the products are engineered, by the materials used and by the characteristics of the laser output beam.

Lasers for coding occupy the infrared range of the electromagnetic spectrum from 10600 nm for CO2 laser coders to 1055 – 1070 nm for Ytterbium fibre lasers. By way of comparison, laser pocket pointers are diode lasers that occupy the range from 630 to 680 nm.

Components of a laser

There are three main components of a laser:

The lasing medium – this can be a gas such as carbon dioxide (CO2); a solid such as Neodymium: Yttrium Aluminium Garnet (Nd:YAG); or a liquid such as a dye. One of the properties of a lasing medium is that it can store energy in a specific way, known as a population inversion. The lasing medium will emit light (photons) as a way of removing excess stored energy.

The excitation mechanism – this is a mechanism by which energy is applied to excite the particles (atoms or molecules) of the lasing medium. Energy can be applied in the form of an electric current, electric discharge, light source, RF energy (radio energy) etc.

The optical resonator – this is the system that extracts the stored energy from the lasing medium in the form of a laser beam. In its simplest form the optical resonator consists of a mirror at either end of the lasing medium. These mirrors are parallel to each other so that photons travelling along the axis of the two mirrors are continuously reflected backwards and forwards (resonate) between the mirrors. One mirror is 100% reflective, the other is partially reflective, so that it only transmits some of the photons which hit it.

Generation of a Laser Beam

Energy applied to the laser medium causes the molecules of the lasing medium to become excited. The energised molecules reach a state at which they cannot hold further energy. They release this energy in the form of particles of light called photons. This process is called spontaneous emission.

As the photons pass through the lasing medium, they cause excited particles of the lasing medium to release excess energy in the form of other photons by a process called stimulated emission. These new photons are identical to the original photons that caused the stimulated emission. They are the same colour (wavelength), they travel in the same direction and they are in phase. The photons transmitted by the partially reflective mirror form the laser beam. The remaining photons are reflected back through the lasing medium to continue the population inversion process.

Dispelling the myth

Incidentally, the visibility of a laser beam depends on the frequency of the laser, the strength of the laser and whether there are particles such as dust in the air.

All laser beams have unique characteristics:

  • Monochromatic (the light is of a single colour or wavelength)
  • Collimated (laser light travels in a straight line without divergence or convergence)
  • Coherent (all light energy particles or photons travel in phase with each other)

In order to see a laser beam it needs to reach our eye, but because of these characteristics, the laser beam appears invisible. The reason you can see laser beams at a concert is that smoke machines are used to scatter the beam: the tiny dust particles in the smoke reflect the laser light. And for that reason a laser beam in space wouldn’t be seen as there is no atmosphere or dust in space. So all those space battles in science fiction films would, in reality, be rather dull. Sorry.