A laser is a light source that can create a narrow and intense beam of electromagnetic radiation. Unlike a flashlight, which has a bulb that emits light in all directions, a laser beam focuses its light into a concentrated stream of photons. LASER stands for Light Amplification by Stimulated Emission of Radiation.
- Light waves are made up of tiny packets of energy called photons.
- Normal light emission happens when atoms or molecules release photons when they transition from higher energy states to lower ones. These emitted photons have random directions and energies, creating a diffuse light.
- The concept that makes lasers unique is stimulated emission. This occurs when an incoming photon interacts with an excited atom in the laser material. The photon’s energy triggers the excited atom in the material to emit a new photon with identical characteristics. The new photon has the same wavelength and so colour, phase and direction as the original.
- Laser material refers to the medium that is used to generate the laser light.
- This phenomenon creates a cascade effect. The newly emitted photon can itself stimulate another excited atom, leading to two identical photons travelling in the same direction. This process repeats, rapidly amplifying the initial light within the laser cavity.
- The cavity comprises two mirrors strategically positioned at the opposite ends of the laser material. One mirror is fully reflective, while the other partially reflects.
- As the amplified light bounces between the mirrors, it continues to stimulate more emissions, resulting in an intense beam of identical photons. The partially reflective mirror allows a portion of this intense light to escape as the laser beam, while the rest continues to contribute to the amplification within the cavity.