Introduction Laser light is one of the most distinctive light sources in science and technology, differing significantly from conventional sources such as electric lamps or sunlight. Lasers possess several unique properties that enable a wide range of applications in medicine, industry, and research. This article aims to explain the four fundamental properties of laser light and highlight the main applications of each property. 1. Monochromaticity A laser produces light of a single wavelength or a very narrow range of wavelengths, making it purely monochromatic, unlike sunlight or lamps, which contain a broad spectrum of colors. Applications: Spectroscopic analysis Medicine (eye surgery) Optical communications 2. Coherence Coherence is the most important property that distinguishes laser light from ordinary light and includes: Spatial Coherence: All photons move in the same direction and are nearly parallel, allowing the laser beam to travel long distances without significant spreading. Temporal Coherence: All photons have the same phase and remain synchronized for a long time, enabling phenomena such as interference. Applications: Holography (3D imaging) Precise distance measurements Laser interference experiments 3. Directionality / Low Divergence A laser beam spreads at a very small angle, making it highly directional. It can be accurately directed over long distances without significant loss of intensity, unlike ordinary light, which spreads in all directions. Applications: Range finding Laser cutting and engraving Industrial welding Laser pointers 4. High Intensity Although the energy of a single photon may not be high, a laser concentrates a large amount of energy into a very small light beam, giving it extremely high power density. Applications: Laser cutting and engraving Precision surgery High-energy scientific research applications Conclusion Lasers represent a unique example of the scientific and technological potential of concentrated light. Understanding its four fundamental properties – monochromaticity, coherence, directionality, and high intensity – allows for its extensive applications in medicine, industry, and scientific research. These properties emphasize the importance of lasers as a precise and efficient light source, making them an essential tool in modern advancements in science and technology. AL_mustaqbal University is the first university in Iraq