What is laser

Well most people are surprised to learn that the word laser is actually an acronym that stands for Light Amplification by Stimulated Emission of Radiation which describes in technical jargon precisely how lasers actually work.

Are all lasers visible to human eye?

Most light (for example from the sun or a light bulb) is usually 'seen' as white light. However, when we put light through a prism we see that it is made of many colours. This is because all light is actually electromagnetic radiation and at different wavelengths of radiation different colours are formed. We can only see a small portion of this spectrum of colours since most of these wavelengths are either too long or too short for the human eye to detect. If the wavelengths are long then light is in the ultraviolet part of the spectrum, whereas if they are short they fall in the infrared part of the spectrum.

Laser light in contrast comes in one colour – in other words it contains one specific wavelength of light (monochromatic). This wavelength is determined by the amount of energy that is released when atomic particles are excited in a laser system. Some of the wavelengths that some laser systems produce are visible to the human eye, others are invisible as they are either ultraviolet or infrared.

At the supermarket, for example, you will see red lasers at the checkout counters. These lasers are used to read the bar codes on your groceries. However most lasers in medicine are at wavelengths close to the infrared portion of the spectrum and are therefore invisible to the human eye.