What are the three characteristics of a laser?

• A. Bright, Narrow spectrum, Isotropic
• B. Coherent, Monochromatic, Collimated
• C. Monochromatic, Collimated, Diffuse
• D. Coherent, Monochromatic, Diffuse

Answer: (B)

Laser light is defined by three key properties: coherence, monochromaticity, and collimation. Coherence means the light waves in the beam maintain a fixed phase relationship with one another, so they can interfere constructively over long distances and maintain a stable, well-defined waveform. Monochromaticity refers to a very narrow spread of wavelengths, giving the beam a single, pure color and predictable interaction with optical materials. Collimation means the rays are nearly parallel, resulting in minimal divergence as the beam travels, which allows it to stay narrow over long distances and be precisely directed.

That combination is why the answer with coherent, monochromatic, and collimated best describes a laser. The other options introduce properties that lasers do not inherently possess: isotropy would mean spreading equally in all directions, which is the opposite of a pointed, directional laser beam; diffuse implies light spreading in many directions with no defined phase, which contradicts coherence and collimation.