Team:TU Delft/Model/Theory
Modeling
What is a laser?
Introduction
Most of us are familiar with the term laser, you have probably seen one or used one as a pointer in a presentation, in a computer mouse or to measure a distance. What makes a laser different from other light sources is its coherence, meaning that it produces a narrow beam that doesn’t disperse over long distances, and that all the light particles, photons, in the beam have identical properties.
The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. This acronym describes the working principles of a laser. The main parts of a laser are the energy pumping source, the gain medium and two mirrors, typically one with a reflectivity of 100% and one with a reflectivity close to 100%. The lasing process starts when a light pumping source is used to excite the gain medium. When the gain medium is excited due to the pumped energy the electrons of its atoms jump to a specific higher energy state due to the energy they absorbed and after a while they drop down to their initial equilibrium position. The energy difference from the specific higher position to the equilibrium is emitted in the form of a photon with exactly that amount of energy, so we can see that the color of the light depends only on the active region’s material. Those produced photons are now leaving the atoms in random directions but some of them bounce back from the two mirrors and are trapped in the device. When those photons meet other excited atoms they make them release the extra energy in the form of a photon and the produced photon moves in the same direction as them. This process is called stimulated emission, so instead of one photon bouncing back and forth now we have two, which is how the light is amplified in the direction perpendicular to the two parallel mirrors. Finally, when the light is amplified enough it leaves the device from the partially reflective mirror as a laser beam. Figure 1 below shows all the basic components of a laser we have discussed.
Video explaining the lasing principle (LASER, 2016):
References
- “LASER.” [Online]. Available: https://en.wikipedia.org/wiki/Laser. [Accessed: 13-Oct-2016].
