A laser (Light Amplification by Stimulated Emission of Radiation) is a device that emits a highly focused beam of coherent, monochromatic, and directional light. The key process behind laser operation is stimulated emission, first proposed by Albert Einstein.
Core Concepts:
- Stimulated Emission:
When an atom in an excited state encounters a photon of the right energy, it can be triggered to emit a second photon of the same energy, phase, and direction. This is the basis for light amplification in lasers. - Monochromaticity:
Laser light has a single wavelength or color, unlike ordinary light, which contains multiple wavelengths. This monochromatic nature makes it suitable for precise applications like spectroscopy and communication. - Coherence:
The emitted photons are in phase with each other, giving laser beams temporal and spatial coherence. This coherence enables interference-based technologies like holography and interferometry. - Population Inversion & Optical Cavity:
- A population inversion is created when more atoms are in an excited state than the ground state, usually by electrical or optical pumping.
- An optical cavity with mirrors reflects light back and forth to stimulate further emission and amplify it before it exits as a laser beam.
Applications:
- Medical: Surgery, eye treatments (LASIK)
- Industrial: Cutting, welding, and engraving
- Scientific: Atomic clocks, spectroscopy
- Everyday use: Barcode scanners, laser printers, optical drives
Lasers are a remarkable example of how quantum principles can lead to powerful technologies with vast practical utility.