Why do laser diodes have four efficiencies?

Laser diodes play an important role in the power electronics industry, particularly in the field of signal transmission due to their excellent monochromaticity, high efficiency, and fast switching characteristics.
The principle of laser diode
Laser diodes emit light based on stimulated radiation, capable of emitting beams of small diameter, highly oriented, and highly coherent light. In 1962, scientists Robert N. Hall and Nick Holonyak Jr. successfully invented the laser diode. Thanks to the "injection" of current in the active region, these devices have achieved "laser" conditions and successfully radiated photons. The difference between laser diode symbol representation and ordinary PN junction diodes is that it contains an undoped intrinsic active region.
Structure and working principle of laser diode
The working principle of a laser diode depends on its internal PIN structure - with P-type and N-type semiconductors at both ends and an undoped intrinsic semiconductor in the middle. When a forward bias is applied, electrons and holes are injected into the active region, and electrons jump from the conductive band to the valence band and recombine with holes, releasing photons.
This process involves three radiation mechanisms: absorption, spontaneous emission, and stimulated emission. Spontaneous emission is the emission of light produced by natural recombination, while stimulated emission is generated when electrons transition from a higher energy level to a lower energy level under the action of photons. Each incident photon can induce two photons of the same phase and wavelength.

The application of laser diodes
Laser diodes are widely used in the field of power electronics. It plays an indispensable role in optoelectronic scenes such as laser printing, optical disc reading and writing, fiber optic communication, and automated sensors. In addition, they play a key role in semiconductor manufacturing technologies such as power device control (such as IGBT and MOSFET driver circuits), EDS, and maskless lithography.
Advantages and disadvantages
Laser diodes offer a wide range of choices in the wavelength range of 810 to 1064 nanometers, while possessing multiple advantages such as fast response and high quantum efficiency. Although laser diodes have limitations such as sensitivity to temperature and light feedback, bandgap shrinkage under high gain current, and higher cost compared to LEDs, their overall performance makes them significantly superior to LEDs in high-precision applications.
The difference between laser diodes and LEDs
Unlike LEDs that rely on spontaneous emission, laser diodes trigger stimulated emission through current and voltage, producing a uniform and coherent light output. With the assistance of laser diodes, fine control optical applications have been achieved, while LEDs are suitable for general lighting and indicator devices.
Through in-depth analysis of laser diode technology, it can be seen that its role in modern power electronics and communication fields is becoming increasingly important. Although the cost of laser diodes is relatively high, their performance advantages are obvious in high-end precision applications, and they are expected to continue to play a huge potential in the future optoelectronics industry.