A technician is setting up a laser to cut material. They need to ensure the laser light travels in a perfectly straight line without spreading out. Which characteristic of laser light is most relevant to this requirement?
- AIts monochromaticity
- BIts high intensity
- CIts coherence
- DIts speed
Show answer & explanationAnswer & explanation
Correct answer: C. Its coherence
Coherence refers to the property of waves having a constant phase relationship. For laser light, this means the light waves are in phase, allowing them to travel as a highly collimated (non-spreading) beam over long distances, which is crucial for precise applications like cutting. While high intensity and monochromaticity are also properties of laser light, coherence is what directly addresses the requirement for a 'perfectly straight line without spreading out'.
Why the other options are wrong
- A. Monochromaticity means the light is of a single wavelength (color), which is important for focus but not directly for preventing spreading.
- B. High intensity means a lot of power in the beam, but doesn't directly prevent spreading.
- D. The speed of light is constant in a given medium and doesn't explain its non-spreading nature.
Coherence of Light
Coherence describes the property of waves (especially light waves) having a constant phase relationship. Coherent light, like that from a laser, maintains a stable and predictable phase difference between different points in the wave.
- Constant phase relationship between waves
- Allows for highly collimated beams (doesn't spread out)
- Essential property of laser light
- Important for interference and diffraction applications
Memory trick: Lasers are 'CMOS' (Coherent, Monochromatic, Ordered, Straight).