Laser is an acronym for light amplification by stimulated emission of radiation. Lasers emit a tightly focused beam of light; since the rays of light emitted by the laser travel in a narrow concentric path, laser light can often attain very high intensities.



The speed or velocity of light in a vacuum is a fundamental constant of the universe that does not change, regardless of the wavelength. This is true for any color of laser light. The relationship between the speed, frequency and wavelength of a photon emitted by a laser is given by the formula c = λ v , where λ is the wavelength and v is the frequency.


Since light interacts with atoms and molecules as it passes through an object, the speed of laser light varies widely in different materials. In most materials, laser light of some colors travels more rapidly than others. Typically, light towards the violet end of the spectrum (i.e., light with shorter wavelengths) travels more slowly than light with longer wavelengths. The ratio between the speed of laser light of a given wavelength in a material vs. its speed in vacuum is called the index of refraction or n and is calculated as n = c / v, where c is the speed in vacuum.

Fun Fact

The fact that different wavelengths of light have different indices of refraction is responsible for the rainbow you see when a beam of white laser light travels through a prism of glass. White light is a mixture of light of different wavelengths, so the different wavelengths will be refracted or bent to a different extent as they travel through the glass and emerge as separate bands on the other side.