Difference between LED and Laser Diodes
1. LED produces Incoherent light via spontaneous emission, whereas Laser Diodes can produce coherent light via stimulated emission. (coherent means that the energy, frequency and phase are same for all photons that are emitted)
2. The output power from a LED is linear with the drive current, whereas for Laser Diodes the output power becomes linear with drive current only after some some threshold is surpassed.
3. Both can be made by same compounds but the difference is the structure of the device. Laser Diodes are produced with special structure that permits it to produce coherent light with small spectral optical bandwidth.
4. The optical spectral width of Laser Diodes(0.1nm to 5nm) are smaller than the LED(25nm to 100nm).
5. Laser Diodes operates faster than the LED. Laser Diodes can operate in the GHz range whereas LED operates in the MHz range.
6. Laser Diodes are more vulnerable and sensitive to temperature than LED
7. Laser Diodes are more expensive than LED
8. Laser Diodes requires external additional threshold and temperature compensation circuitry.
9. LED are more reliable than Laser Diodes
10. LED is eye safe whereas Laser Diodes can affect eye depending upon the frequency of operation