What's the difference between LED and LD's light emission principle?
LED is commonly known as semiconductor led;LD commonly known as semiconductor laser diodes.The luminescence mechanism of both no essential difference, which is driven by positive bias current, the junction of P and N region of the semiconductor pn junction (i.e. particle excitation, electron and charged holes in the current drive to high level transition, then from the high level to low level, while the release of a photon, i.e. the light.There are lasers work with common light source is different, it also need laser material (the semiconductor laser diode LD, laser material is a semiconductor material), pump (i.e. external energy source), resonant cavity.LD and LED work, work material and semiconductor pump source has its system structure, the only difference is that LD form a resonant cavity in the outer layer through natural cleavage, the resonant cavity light-emitting threshold conditions (i.e. certain threshold conditions) when this condition is reached, the laser began inversion stimulated luminescence. When the LD driver has not reached the threshold conditions, its light-emitting mechanism and LED is in fact no obvious difference.
LD working principle is very simple, is in high level electronic transitions to a lower level, stimulated emitted photon, photon in cavity oscillation, constructive interference, when the gain is larger than the loss of the emitted laser.
In some PN junctions of semiconductor materials, the injected minority carriers combine with the majority carriers to release excess energy in the form of light, thereby converting the electric energy directly into light energy. PN junction plus reverse voltage, the minority carrier is difficult to inject, so it does not emit light. The diode, produced by injection electroluminescent principle, is called light-emitting diode, commonly known as LED.
In terms of beam quality, the beam degeneracy of LED is inferior to LD; in other words, the light emitted by LD has better wavelength characteristics, directional collimation characteristics, phase characteristics and so on
