Major advances in these areas have depended on the realization of more robust and practical sources of coherent radiation. New coherent light sources have enabled innovative research within frequency and time regimes that had been beyond the capabilities of previous optical devices. Generally, once a new light source is realized, research focuses on improving the source s frequency purity or towards short-pulse generation for diagnostic or communication applications. Under various conditions, light possesses different properties. It can behave as a stream of particles or as a series of waves.
Scientists describe light as being made of photons that form waves.
As witnessed through a prism, normal light is polychromatic and is of lower intensity than laser light. It also emerges from a transparent medium with the same wavelength it had before it passed through the medium. Laser light, however, consists of highly concentrated photons traveling in a narrow beam. Light waves from an unmodulated laser can be almost all of the same frequency and, hence, are monochromatic. Ordinary light waves can be likened to a scrambling football team or a teeming mob of people moving in different directions.